Journal articles: 'Reaction calculations'

1

Morton, A. J., and DG Sargood. "Thermonuclear Reaction Rates for Reactions Leading to N = 28 Nuclei." Australian Journal of Physics 48, no. 1 (1995): 125. http://dx.doi.org/10.1071/ph950125.

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Nuclear reaction cross sections derived from statistical-model calculations have been used in the calculation of thermonuclear reaction rates for 36 nuclei at temperatures that are representative of the interiors of evolving stars and supernovae as nucleosynthesis approaches the production of nuclei with N = 28. The statistical-model calculations used optical-model parameters in the particle channels which had been selected to give the best overall agreement between theoretical and experimental cross sections for reactions on stable target nuclei in the mass and energy ranges of importance for the stellar conditions of interest. The optical-model parameters used, and the stellar reaction rates obtained, are tabulated. Comparisons are made between these stellar rates and those from other statistical-model calculations in the literature.

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2

Longland, Richard, and Nicolas de Séréville. "Correlated energy uncertainties in reaction rate calculations." Astronomy & Astrophysics 642 (October 2020): A41. http://dx.doi.org/10.1051/0004-6361/202038151.

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Context. Monte Carlo methods can be used to evaluate the uncertainty of a reaction rate that arises from many uncertain nuclear inputs. However, until now no attempt has been made to find the effect of correlated energy uncertainties in input resonance parameters. Aims. Our goal is to investigate the impact of correlated resonance energy uncertainties on reaction rates. Methods. Using a combination of numerical and Monte Carlo variation of resonance energies, the effect of correlations are investigated. Five reactions are considered: two fictional, illustrative cases and three reactions whose rates are of current interest. Results. The effect of correlations in resonance energies depends on the specific reaction cross section and temperatures considered. When several resonances contribute equally to a reaction rate, and when they are located on either side of the Gamow peak, correlations between their energies dilute their effect on reaction rate uncertainties. If they are both located above or below the maximum of the Gamow peak, however, correlations between their resonance energies can increase the reaction rate uncertainties. This effect can be hard to predict for complex reactions with wide and narrow resonances contributing to the reaction rate.

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MANTHE, UWE. "REACTION RATES: ACCURATE QUANTUM DYNAMICAL CALCULATIONS FOR POLYATOMIC SYSTEMS." Journal of Theoretical and Computational Chemistry 01, no. 01 (July 2002): 153–72. http://dx.doi.org/10.1142/s0219633602000087.

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Rate constants of chemical reactions can be computed directly: employing flux correlation functions, no scattering calculations are required. If the reaction is direct, the dynamical simulation can be restricted to the vicinity of the reaction barrier. Therefore accurate thermal rate constants and cumulative reaction probabilities can be calculated for rather large systems. Recent calculations have studied systems with up to six atoms, e.g., H + CH 4 → H 2 + CH 3. The calculations provide a full-dimensional quantum description of the reaction process. In the article, an introduction to the theory of flux correlation functions is given. Methods for the efficient computation of accurate thermal rate constants and cumulative reaction probabilities are reviewed. Connections to transition state ideas are highlighted. The multi-configurational time-dependent Hartree (MCTDH) approach, which facilitates efficient multi-dimensional wave packet propagation, is described and its use in reaction rate calculation is discussed. As examples, recent results for the prototypical polyatomic reaction H + CH 4 → H 2 + CH 3 are presented and rotational effects on the reaction rates of H 2 + OH → H + H 2 O , O + HCl → OH + Cl , and H 2 + Cl → H + HCl are discussed.

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Sirirak, Jitnapa, Narin Lawan, Marc W. Van der Kamp, Jeremy N. Harvey, and Adrian J. Mulholland. "Benchmarking quantum mechanical methods for calculating reaction energies of reactions catalyzed by enzymes." PeerJ Physical Chemistry 2 (May 20, 2020): e8. http://dx.doi.org/10.7717/peerj-pchem.8.

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To assess the accuracy of different quantum mechanical methods for biochemical modeling, the reaction energies of 20 small model reactions (chosen to represent chemical steps catalyzed by commonly studied enzymes) were calculated. The methods tested included several popular Density Functional Theory (DFT) functionals, second-order Møller Plesset perturbation theory (MP2) and its spin-component scaled variant (SCS-MP2), and coupled cluster singles and doubles and perturbative triples (CCSD(T)). Different basis sets were tested. CCSD(T)/aug-cc-pVTZ results for all 20 reactions were used to benchmark the other methods. It was found that MP2 and SCS-MP2 reaction energy calculation results are similar in quality to CCSD(T) (mean absolute error (MAE) of 1.2 and 1.3 kcal mol−1, respectively). MP2 calculations gave a large error in one case, and are more subject to basis set effects, so in general SCS-MP2 calculations are a good choice when CCSD(T) calculations are not feasible. Results with different DFT functionals were of reasonably good quality (MAEs of 2.5–5.1 kcal mol−1), whereas popular semi-empirical methods (AM1, PM3, SCC-DFTB) gave much larger errors (MAEs of 11.6–14.6 kcal mol−1). These results should be useful in guiding methodological choices and assessing the accuracy of QM/MM calculations on enzyme-catalyzed reactions.

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Melissas, Vasilios S., Donald G. Truhlar, and Bruce C. Garrett. "Optimized calculations of reaction paths and reaction‐path functions for chemical reactions." Journal of Chemical Physics 96, no. 8 (April 15, 1992): 5758–72. http://dx.doi.org/10.1063/1.462674.

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Koukkari, Pertti, Risto Pajarre, and Peter Blomberg. "Reaction rates as virtual constraints in Gibbs energy minimization." Pure and Applied Chemistry 83, no. 5 (April 4, 2011): 1063–74. http://dx.doi.org/10.1351/pac-con-10-09-09.

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The constrained Gibbs energy method has been developed for the use of immaterial entities in the formula conservation matrix of the Gibbs energy minimization problem. The new method enables the association of the conservation matrix with structural, physical, chemical, and energetic properties, and thus the scope of free energy calculations can be extended beyond the conventional studies of global chemical equilibria and phase diagrams. The use of immaterial constraints enables thermochemical calculations in partial equilibrium systems as well as in systems controlled by work factors. In addition, they allow the introduction of mechanistic reaction kinetics to the Gibbsian multiphase analysis. The constrained advancements of reactions are incorporated into the Gibbs energy calculation by using additional virtual phases in the conservation matrix. The virtual components are then utilized to meet the incremental consumption of reactants or the formation of products in the kinetically slow reactions. The respective thermodynamic properties for the intermediate states can be used in reaction rate formulations, e.g., by applying the reaction quotients.

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7

Chen, Shuang Kou, Jian Fang Zhu, Wen Zhang Huang, Bai He, Li Jun Xiang, and Upendra Adhikari. "The Direct Oxidizing Mechanism for the Reaction of Ozone and Phenol: A DFT Study." Advanced Materials Research 554-556 (July 2012): 1632–36. http://dx.doi.org/10.4028/www.scientific.net/amr.554-556.1632.

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Using DFT/6-31+G (d, p) method, the structure of phenol are gained in the global optimization and properties were theoretically studied. The atomic electric charges, activation of reaction and thermodynamics parameters are obtained. The calculation shows that benzene ring in phenol tends to have electrophonic attacking substitution reaction O3 directly and form catechol and hydroquinol. The calculation of thermodynamics properties indicate that two pathways are exothermic reactions, and the Gibbs free energies (ΔG) are always less than zero, two reactions are easily occurred spontaneously. Dynamics calculations show that there is only one transition state in each reaction; through vibrational analysis we confirm the transition state. After corrected single point energy, we find that the reaction activation energies of the two reactions are small (Ea1=4.48kcal/mol and Ea2=2.87kal/mol), indicating that ortho-position and para-position products exist simultaneously, which is in accordance with the thermodynamics calculation result.

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8

Şekerci, Mert, Hasan Özdoğan, and Abdullah Kaplan. "Level density model effects on the production cross-section calculations of some medical isotopes via (α, xn) reactions where x = 1–3." Modern Physics Letters A 35, no. 24 (June 23, 2020): 2050202. http://dx.doi.org/10.1142/s0217732320502028.

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Level density models have an undeniable importance for a better perception on the nature of nuclear reactions, which influences our life via various ways. Many novel and advanced medical application use radioisotopes, which are produced with nuclear reactions. By considering the connection between the level density models and the importance of theoretical calculations for the production routes of medically important isotopes, this study is performed to investigate the level density model effects on the production cross-section calculations of [Formula: see text]Zn, [Formula: see text]Ga, [Formula: see text]Kr, [Formula: see text]Pd, [Formula: see text]In, [Formula: see text]I and [Formula: see text]At radioisotopes via some alpha particle induced and neutron emitting reactions. For theoretical calculations; frequently used computation tools, such as TALYS and EMPIRE codes, are applied. Obtained theoretical results are then compared with the experimental data, taken from Experimental Nuclear Reaction Data (EXFOR) library. For a better interpretation of the results, a mean weighted deviation calculation for each investigated reaction is performed in addition to a visual comparison of the graphical representations of the outcomes.

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9

Mikhailov, S., R. Brovko, S. Mushinskii, and M. Sulman. "N-Methyl-D-Glucoseimine Synthesis Reaction Thermodynamic Properties Calculation." Bulletin of Science and Practice 6, no. 11 (November 15, 2020): 40–46. http://dx.doi.org/10.33619/2414-2948/60/04.

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The presented article is devoted to thermodynamic calculations of the N-methyl-D-glucosimine reversible formation reaction, an intermediate product for N-methyl-D-glucosamine synthesis, which is widely used in pharmaceutical practice as a ballast or counterion that improves the bioavailability of the main active substance. N-methyl-D-glucosimine is synthesized as a result of the interaction of D-glucose with methylamine in organic solvents, the reaction is reversible, and the yield of the target product depends entirely on the reaction conditions. The use of thermodynamic calculations makes it possible to evaluate the influence of the chemical process conditions on the yield of target products, which in turn contributes to a deeper understanding of the chemical reactions mechanisms. In chemical equilibrium, direct and reverse reactions proceed at equal rates, while the concentrations of products and reagents remain constant. When the reaction proceeds in a closed system, after a certain time, a state of equilibrium occurs, while the reaction does not proceed with a complete transformation of the reagents. This article presents the results of thermodynamic calculations of the reaction for the synthesis of N-methyl-D-glucosimine by the Van Kravlen – Cheremnov method. The Gibbs energy, equilibrium constants, and D-glucose conversion were calculated as activity function of reacting substances. It was shown that an increase in the temperature of the reaction mixture from 20 to 160 °C promotes an increase in the conversion of D-glucose from 3 to 32%, and therefore it is possible to recommend carrying out this reaction at elevated temperatures.

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10

Nagaoka, Masataka, Yoshishige Okuno, Tokio Yamabe, and Kenichi Fukui. "Abinitio calculations and the chemical reaction molecular dynamics simulation." Canadian Journal of Chemistry 70, no. 2 (February 1, 1992): 377–87. http://dx.doi.org/10.1139/v92-054.

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To clarify the mechanism of chemical reactions in solution, each solvent molecule was classified as either a reactive-solvent molecule or a medium-solvent molecule in accordance with its role in the reaction. The proton transfer reaction of formamidine in water was treated as a model reaction. Abinitio molecular orbital calculations were performed for the complex made up of a formamidine, a reactive-water molecule, and a medium-water molecule. The optimized geometries and the solvation energies were obtained and the orbital interaction analysis carried out along the intrinsic reaction coordinate (IRC). It was found that the medium-water molecule influences the reaction dynamically rather than energetically. There was no energy change in the potential barrier under the influence of the medium-water molecule, in contrast to the remarkable barrier-reducing effect of the reactive-water molecule. The situation is different from that in chemical reactions involving ionic states. Chemical reaction molecular dynamics (CRMD) simulation for this system was performed in order to investigate the energy relaxation mechanism. It was found that just after the reaction finishes, a relative translational motion is first induced between the super molecule, which consists of a formamidine and a reactive-water molecule, and the medium-water molecule, and is then followed by a rotational motion of the medium-water molecule. Keywords: formamidine, chemical reaction molecular dynamics method, reactive-solvent molecule, medium-solvent molecule, energy relaxation mechanism.

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11

KAMIMURA, M., Y. KINO, and E. HIYAMA. "STAU-CATALYZED BIG-BANG NUCLEOSYNTHESIS AND NUCLEAR CLUSTER MODEL." International Journal of Modern Physics A 24, no. 11 (April 30, 2009): 2076–83. http://dx.doi.org/10.1142/s0217751x09045649.

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Three-body cluster-model calculations are performed for the new types of big-bang nucleosynthesis (BBN) reactions that are calalyzed by a supersymmetric (SUSY) particle stau, a scalar partner of the tau lepton. If a stau has a lifetime ≳ 103s, it would capture a light element previously synthesized in standard BBN and form a Coulombic bound state. The bound state, an exotic atom, is expected to induce various reactions, such as (αX-) + d → 6 Li + X-, in which a negatively charged stau (denoted as X-) works as a catalyzer. Recent literature papers have claimed that some of these stau-catalyzed reactions have significantly large cross sections so that inclusion of the reactions into the BBN network calculation can change drastically abundances of some elements, giving not only a solution to the 6 Li -7 Li problem (calculated underproduction of 6 Li by ~ 1000 times and overproduction of 7 Li +7 Be by ~ 3 times) but also a constraint on the lifetime and the primordial abundance of the elementary particle stau. However, most of these literature calculations of the reaction cross sections were made assuming too naive models or approximations that are unsuitable for those complicated low-energy nuclear reactions. We use a few-body calculational method developed by the authors, and provides precise cross sections and rates of the stau-catalyzed BBN reactions for the use in the BBN network calculation.

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12

Fu, Yu-Wei, Wei-Feng Sun, and Xuan Wang. "UV-Initiated Crosslinking Reaction Mechanism and Electrical Breakdown Performance of Crosslinked Polyethylene." Polymers 12, no. 2 (February 12, 2020): 420. http://dx.doi.org/10.3390/polym12020420.

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The ultraviolet (UV) irradiation crosslinking reactions of polyethylene and the electronic properties of photo-initiators and reaction products are theoretically investigated by the first-principles calculations. The crosslinked polyethylene (XLPE) materials are prepared in experiments that employ the UV-initiated crosslinking technique with different photon-initiation systems. Infrared spectrum and the alternating current dielectric breakdown strength of UV-initiated XLPE are tested to explore the effect of reaction products on the breakdown characteristics in combination with the electron structure calculations. The theoretical calculations indicate that the 4-hydroxybenzophenone laurate, which is compatible with polyethylene, can effectively initiate crosslinking reactions of polyethylene molecules under UV photon excitation and will produce reaction by-products from carbonyl radicals; as a macromolecular auxiliary crosslinker, the monomer or homopolymer of dioleyl-2,2′,4,4′-tetraallyl isocyanurate can form chemical connections with multiple polyethylene molecules acting as a crosslinking node in a photon-initiated reaction process. The carbonyl, hydroxyl, or ester groups of reaction by-products are capable of capturing hot electrons to prevent polyethylene molecules from impact ionization, and thus will increase the breakdown electric field. The macromolecular auxiliary crosslinker and the macromolecular photon initiator as well as its reaction by-product can convert the energy of their captured high-energy electrons into heat, which can act as a voltage stabilizer. The molecule characterization of infrared spectra demonstrates that the characteristic absorption peaks of the carbonyl in the macromolecular photon initiator and the allyl in the macromolecular auxiliary crosslinking agent are gradually decreasing in intensity as the crosslinking reaction proceeds, which is consistent with the conclusion from theoretical calculations. Compared with the small molecular photon-initiation system generally used in the photon-initiated crosslinking process, the higher dielectric breakdown field of XLPE being prepared by utilizing a macromolecular photon-initiation system is in good agreement with the calculation results of electronic affinity and ionization potential. The consistent results of the experiments and first-principles calculations elucidate the fundamental mechanism of the UV-initiation crosslinking technique and suggest a prospective routine to improve the insulation strength for developing high-voltage XLPE insulating materials.

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13

CAO, YALI, XIANG ZHAO, ZICHAO TANG, BIN XIN, and SHAOXIANG XIONG. "GAS-PHASE REACTIONS OF V+ AND VO+ WITH METHANOL." International Journal of Modern Physics B 19, no. 15n17 (July 10, 2005): 2693–98. http://dx.doi.org/10.1142/s0217979205031547.

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The reactions of V + and VO + with methanol have been investigated experimentally by FT-ICR mass spectrometer and theoretically by ab initio calculation. Both V + and VO + exhibit impressive reactivity with methanol. The products distribution of different reaction time indicate that in whole reaction processes methanol is adsorbed one by one, and no more than four methanol molecules can be solved in the first shell of central ion V +. The reaction mechanisms have been proposed, and the possible geometrical structures of products are also analyzed by DFT calculations.

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Werstiuk, Nick Henry, and Wojciech Sokol. "Density functional theory computational study on Diels–Alder reactions of cyclopentadiene with selected vinylsilanes and methylenecyclopropane." Canadian Journal of Chemistry 89, no. 3 (February 2011): 409–14. http://dx.doi.org/10.1139/v10-167.

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Aimed at predicting relative reactivities, density functional theory (DFT) calculations were carried out on a series of Diels–Alder reactions involving silylvinyl derivatives reacting with cyclopentadiene as part of a synthetic research project. Using three reactions for which experimental rate data are available to calibrate our calculations, we computationally pinpointed the best synthetic route to bicyclo[2.2.1]hept-5-ene-2,2-diylbis(trimethylsilane) (1). The synthesis begins with the Diels–Alder reaction of cyclopentadiene (2) with commercially available (1-bromovinyl)trimethylsilane (6).

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Morgon, Nelson H., Aguinaldo R. De Souza, and Júlio R. Sambrano. "NH3+N2O3 reaction. High level calculations." Journal of Molecular Structure: THEOCHEM 759, no. 1-3 (February 2006): 189–94. http://dx.doi.org/10.1016/j.theochem.2005.08.036.

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Pieraggi, B. "Calculations of parabolic reaction rate constants." Oxidation of Metals 27, no. 3-4 (April 1987): 177–85. http://dx.doi.org/10.1007/bf00667057.

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Siddik, Tarik. "(n, p) Reaction Cross Sections Calculations of Some Stellar Iron Group Fusion Materials." Journal of Advanced Physics 6, no. 1 (March 1, 2017): 18–25. http://dx.doi.org/10.1166/jap.2017.1283.

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The excitation functions for (n, p) reactions from reaction threshold to 24 MeV on some important iron (Fe) group target elements (20 ≤ Z ≤ 28) for astrophysical (n, p) reactions such as Si, Ca, Sc, Ti, Cr, Fe, Co and Ni were calculated using TALYS-1.0 nuclear model code. The new calculations on the excitation functions of 28Si(n, p)28Al, 29Si(n, p)29Al, 42Ca(n, p)42K, 45Sc(n, p)45Ca, 46Ti(n, p)46Sc, 53Cr(n, p)53V, 54Fe(n, p)54Mn, 57Fe(n, p)57Mn, 59Co(n, p)59Fe, 58Ni(n, p)58Co and 60Ni(n, p)60Co reactions have been carried out up to 24 MeV incident neutron energy. In these calculations, the compound nucleus and pre-equilibrium reaction mechanism studied extensively. According to these calculations, we assume that these model calculations can be applied to some heavy elements, ejected into interstellar medium by dramatic supernova events.

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Lasaga, Antonio C. "Metamorphic reaction rate laws and development of isograds." Mineralogical Magazine 50, no. 357 (September 1986): 359–73. http://dx.doi.org/10.1180/minmag.1986.050.357.02.

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AbstractNew data on the kinetics of dehydration of muscovite + quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of ‘reaction zones’ are then analysed as a function of intrusion size and kinetic parameters.

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Gorodetsky, Alexander, Mariya Barabash, Maryna Romashkina, and Andrii Tomashevskyi. "“CHARACTERISTIC LOAD” PRINCIPLE." International Journal for Computational Civil and Structural Engineering 16, no. 2 (June 26, 2020): 50–62. http://dx.doi.org/10.22337/2587-9618-2020-16-2-50-62.

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The article discusses examples of the application of the principle of "characteristic load" (calculations taking into account engineering non-linearity; the designation of subgrade reaction moduli; the designation of the sizes of shelves for beam grillage). The principle of "characteristic load" on the one hand implements the consideration of various factors that are not available when calculating in a linear formulation, on the other hand, it preserves the traditional calculation technology

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Firihu, Muhammad Zamrun, Viska Inda Variani, and J. Justina. "Simulasi Numerik Reaksi Fusi Nuklir dengan menggunakan Metode Wong." INDONESIAN JOURNAL OF APPLIED PHYSICS 6, no. 01 (September 14, 2016): 50. http://dx.doi.org/10.13057/ijap.v6i01.1800.

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The numerical simulation for calculating the cross section of fusion reaction is done by using Wong formula. We especially calculated the cross section for the fusion reaction of light systems, i.e. 12C+12C, 16O+12C and 16O+16O reactions. We compared the obtained cross section with experimental data. In order to check the accuracy of the calculations, the chi-square analisys is then permormed. We found that the simulation results of the fusion cross section obtained using Wong Formula well explain the experimetal data of the fusion cross section for the 12C+12C, 16O+12C and 16O+16O reactions. This finding indicates that the Wong formula can be used for studing the fusion reaction of light systems.

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21

Bosch, Enric, Miquel Moreno, José M. Lluch, and Juan Bertrán. "Intrinsic reaction coordinate calculations for reaction paths possessing branching points." Chemical Physics Letters 160, no. 5-6 (August 1989): 543–48. http://dx.doi.org/10.1016/0009-2614(89)80060-0.

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Şekerci, Mert. "An investigation of the effects of level density models and alpha optical model potentials on the cross-section calculations for the production of the radionuclides 62Cu, 67Ga, 86Y and 89Zr via some alpha induced reactions." Radiochimica Acta 108, no. 6 (June 25, 2020): 459–67. http://dx.doi.org/10.1515/ract-2019-3169.

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AbstractTheoretical studies via nuclear reaction models have an undeniable importance and impact in terms of better understanding of reaction processes and their nature. In this study, by considering the importance of these models and the medical radionuclides, the effects of six level density models and eight alpha optical model potentials on the cross-section calculations for the production of the radionuclides 62Cu, 67Ga, 86Y and 89Zr via 59Co(α,n)62Cu, 60Ni(α,np)62Cu, 65Cu(α,2n)67Ga, 64Zn(α,p)67Ga, 85Rb(α,3n)86Y, 86Sr(α,n)89Zr, 87Sr(α,2n)89Zr and 88Sr(α,3n)89Zr reactions were investigated. Calculations for each reaction route were performed by using the TALYS v1.9 code. The most consistent model with the literature data taken from the Experimental Nuclear Reaction Database (EXFOR), was identified by using the reduced chi-squared statistics in addition to an eyeball estimation. Also, the effects of combinational use of selected models and potentials were investigated by comparing the calculational results with the experimental data.

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TANG, PING-YING, WEI-LONG QUAN, BI-YU TANG, and KE-LI HAN. "STRONG VIBRATIONAL ENHANCEMENT OF SUBSTANTIALLY ENDOTHERMIC REACTION K + HF: A TIME-DEPENDENT QUANTUM WAVE PACKET STUDY." Journal of Theoretical and Computational Chemistry 05, no. 02 (June 2006): 243–53. http://dx.doi.org/10.1142/s0219633606002167.

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Detailed dynamics of the substantially endothermic reaction K + HF on a new ab initio ground potential energy surface has been studied by means of time-dependent quantum wave packet calculation. The calculations showed that the reaction could be significantly enhanced by vibrational excitation of HF , but not very sensitive to initial rotational excitation. The relative and absolute integral cross sections and the logarithm of the σ(v = 1)/σ(v = 0) ratio have been calculated and compared with available experimental and theoretical results. Relatively good agreement with experiment and other calculations was obtained. Reaction rate constants of this reaction was also calculated and discussed.

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MBOUOMBOUO, Ibrahim NDASSA, Gouet Bebga, Martin Signé, François Volatron, and Bernard Silvi. "THEORETICAL STUDY OF CHLORINATION REACTION OF NITROBENZENE FROM DFT CALCULATIONS." JOURNAL OF ADVANCES IN CHEMISTRY 11, no. 9 (July 29, 2015): 3784–93. http://dx.doi.org/10.24297/jac.v11i9.2690.

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The geometric parameters of stationary points on the potential surface energy of the chlorination reaction of nitrobenzene in the presence of Aluminium chloride as catalyst were investigated theoretically by hybrid DFT (Density Functional Theory) calculations in order to determine his general reaction mechanism in gas phase and in solution. The results obtained by DFT have been compared with CCSD(T) method which is the most powerful post-Hartree Fock method in terms of inclusion of dynamic correlation. Although the electrophilic substitution reaction is widely taught in most courses in organic chemistry, the mechanism has been very few studied theoretically. The results obtained in gas phase are consistent with the traditional description of these reactions: the orientation of this substitution in meta position depends on the stability of a reaction intermediate (Wheland said). Without taking in consideration the reactants and products, six stationary points are found on the potential surface energy of this reaction. The reaction has also been studied in the presence of solvent and we’ve noted that the influence of solvent decreases the electrostatic attraction on the Wheland complex, but the general reaction mechanism remains unchanged in solution.

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Guo, Feng, Hong Zhang, Chao-Yang Zhang, Xin-Lu Cheng, and Hai-Quan Hu. "Effect of electronic excitation to intermolecular proton transfer in bulk nitromethane: Tuned parameter SCC-DFTB and first principles study." Journal of Theoretical and Computational Chemistry 14, no. 02 (March 2015): 1550013. http://dx.doi.org/10.1142/s0219633615500133.

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To understand the reaction mechanism involving hydrogen transfers through hydrogen-bond bridge, we carried out both Self-Consistent Charge Density Functional Tight-Binding (SCC-DFTB) calculations of bulk nitromethane and Density Functional Theory (DFT) calculations of singlet ground state/triplet excited state molecular nitromethane using B3LYP functional. Firstly, we tuned the repulsive parameters of the SCC-DFTB method for nitromethane with dataset calculated from DFT at B3LYP/6-311g level. The molecular dynamics simulations are carried out with tuned parameters to get the dynamical properties of the bulk nitromethane, and the static calculations are intended to give energy profile of the reaction process. These calculations indicate the excitation of nitromethane molecule making the proton transfer reactions possible, and lowering the reaction barrier.

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James, S., M. S. Anand, M. K. Razdan, and S. B. Pope. "In Situ Detailed Chemistry Calculations in Combustor Flow Analyses." Journal of Engineering for Gas Turbines and Power 123, no. 4 (March 1, 1999): 747–56. http://dx.doi.org/10.1115/1.1384878.

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In the numerical simulation of turbulent reacting flows, the high computational cost of integrating the reaction equations precludes the inclusion of detailed chemistry schemes, therefore reduced reaction mechanisms have been the more popular route for describing combustion chemistry, albeit at the loss of generality. The in situ adaptive tabulation scheme (ISAT) has significantly alleviated this problem by facilitating the efficient integration of the reaction equations via a unique combination of direct integration and dynamic creation of a look-up table, thus allowing for the implementation of detailed chemistry schemes in turbulent reacting flow calculations. In the present paper, the probability density function (PDF) method for turbulent combustion modeling is combined with the ISAT in a combustor design system, and calculations of a piloted jet diffusion flame and a low-emissions premixed gas turbine combustor are performed. It is demonstrated that the results are in good agreement with experimental data and computations of practical turbulent reacting flows with detailed chemistry schemes are affordable.

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Cerri, G., V. Michelassi, S. Monacchia, and S. Pica. "Kinetic combustion neural modelling integrated into computational fluid dynamics." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 217, no. 2 (January 1, 2003): 185–92. http://dx.doi.org/10.1243/09576500360611218.

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The attempt to replace traditional chemical kinetics model calculations with new ones based on neural networks (NNs) has been successfully carried out. The paper deals with the methodology that has been followed to replace traditional model calculations with neural models (NMs) for methane/air combustion. The reacting flowfield has been described with account taken of the detailed chemical reaction mechanism. Convective and turbulent diffusive transport of species has been taken into consideration by means of a well-known finite volume computational fluid dynamics (CFD) code. Two versions of such a mechanism have been developed. The first one is based on traditional differential equations representing the species production rates. Such equations are integrated over the time intervals related to the cell volumes and local volumetric flows. The second version is based on neural models which can extract and store knowledge from the data presented to them. The neural model capability of connecting output to input quantities by means of the stored knowledge leads to very fast calculations. A reduced combustion mechanism involving 20 species and 68 reactions has been developed both for the traditional calculation and for the neural model calculations. It can be concluded that calculations using chemical kinetics neural models show a 42 times shorter CPU time than that of the traditional procedures, with a comparable solution accuracy of the combustion flowfields.

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Fakiola, C., I. Karakasis, I. Sideris, A. Khaliel, and T. J. Mertzimekis. "Statistical-model calculations for α-capture reactions relevant to the p process." HNPS Proceedings 26 (April 1, 2019): 228. http://dx.doi.org/10.12681/hnps.1825.

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About 35 nuclides which lie on the neutron deficient side of the isotopic chart cannot be created by the two basic nucleosynthetic processes, the sand the rprocess. Due to scarce experimental data and the vast complexity of the reaction network involved, cross sections and reactions are estimated theoretically, using the Hauser–Feshbach statistical model. In the present work, theoretical calculations of cross sections of radiative α-capture reactions on the neutron–deficient Erbium and Xenon isotopes are presented in an attempt to make predictions inside the astrophysically relevant energy window (Gamow). The particular reactions are predicted to be sensitive branchings in the γprocess path.The most recent versions of TALYS (v1.9) and Fresco codes were employed for all calculations, initially focusing on investigating the influence of the default eight (8) α–nucleus optical potential models of TALYS on reaction cross sections. The theoretical results of both codes are compared and for the reactions where experimental data exist in literature, the optical model parameters were adjusted appropriately to best describe the data and were subsequently used for estimating (α,γ) reaction cross sections. Predictions for the (α,n) reaction channels have also been calculated and studied.

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Banerji, Biswadip, K. Chandrasekhar, Sunil Kumar Killi, Sumit Kumar Pramanik, Pal Uttam, Sudeshna Sen, and Nakul Chandra Maiti. "Silver-catalysed azide–alkyne cycloaddition (AgAAC): assessing the mechanism by density functional theory calculations." Royal Society Open Science 3, no. 9 (September 2016): 160090. http://dx.doi.org/10.1098/rsos.160090.

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‘Click reactions’ are the copper catalysed dipolar cycloaddition reaction of azides and alkynes to incorporate nitrogens into a cyclic hydrocarbon scaffold forming a triazole ring. Owing to its efficiency and versatility, this reaction and the products, triazole-containing heterocycles, have immense importance in medicinal chemistry. Copper is the only known catalyst to carry out this reaction, the mechanism of which remains unclear. We report here that the ‘click reactions’ can also be catalysed by silver halides in non-aqueous medium. It constitutes an alternative to the well-known CuAAC click reaction. The yield of the reaction varies on the type of counter ion present in the silver salt. This reaction exhibits significant features, such as high regioselectivity, mild reaction conditions, easy availability of substrates and reasonably good yields. In this communication, the findings of a new catalyst along with the effect of solvent and counter ions will help to decipher the still obscure mechanism of this important reaction.

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30

Elster, Ch, L. Hlophe, V. Eremenko, F. M. Nunes, I. J. Thompson, G. Arbanas, and J. E. Escher. "Separable Potentials for (d,p) Reaction Calculations." Journal of Physics: Conference Series 724 (June 2016): 012014. http://dx.doi.org/10.1088/1742-6596/724/1/012014.

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31

Han, Yinlu. "Theoretical Calculations ofn+232,234,236,238,240U Reaction Cross Sections." Nuclear Science and Engineering 158, no. 1 (January 2008): 78–87. http://dx.doi.org/10.13182/nse08-a2740.

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Han, Yinlu, Yongli Xu, Haiying Liang, Hairui Guo, Chonghai Cai, and Qingbiao Shen. "Theoretical Calculations and Analysis ofn+27Al Reaction." Nuclear Science and Engineering 172, no. 1 (September 2012): 102–21. http://dx.doi.org/10.13182/nse11-28.

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33

Christley, J. A., and J. A. Tostevin. "Reaction cross section calculations for deformed nuclei." Physical Review C 59, no. 4 (April 1, 1999): 2309–12. http://dx.doi.org/10.1103/physrevc.59.2309.

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34

Rauscher, Thomas, and Friedrich-Karl Thielemann. "Astrophysical Reaction Rates From Statistical Model Calculations." Atomic Data and Nuclear Data Tables 75, no. 1-2 (May 2000): 1–351. http://dx.doi.org/10.1006/adnd.2000.0834.

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35

Liang, Haiying, Zhendong Wu, Zhengjun Zhang, Yinlu Han, and Xuesheng Jiao. "Calculations and Analysis of n+93Nb Reaction." Nuclear Science and Engineering 187, no. 2 (May 26, 2017): 107–26. http://dx.doi.org/10.1080/00295639.2017.1295699.

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36

Yamataka, Hiroshi, and Shigeru Nagase. "Theoretical Calculations on the Wittig Reaction Revisited." Journal of the American Chemical Society 120, no. 30 (August 1998): 7530–36. http://dx.doi.org/10.1021/ja974237f.

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37

Zhixing, Chen. "Rotation procedure in intrinsic reaction coordinate calculations." Theoretica Chimica Acta 75, no. 6 (1989): 481–84. http://dx.doi.org/10.1007/bf00527679.

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38

Thompson, Ian J. "Coupled reaction channels calculations in nuclear physics." Computer Physics Reports 7, no. 4 (April 1988): 167–212. http://dx.doi.org/10.1016/0167-7977(88)90005-6.

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39

Song, Wei, Yuchun Lin, Andrij Baumketner, Wei Cai, and Donald J. Jacobs. "Optimized Image Charges for Reaction Field Calculations." Biophysical Journal 100, no. 3 (February 2011): 157a. http://dx.doi.org/10.1016/j.bpj.2010.12.1073.

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40

Dalgleish, Douglas G. "A new calculation of the kinetics of the renneting reaction." Journal of Dairy Research 55, no. 4 (November 1988): 521–28. http://dx.doi.org/10.1017/s002202990003329x.

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SummaryA detailed calculation of the growth of molecular weight during the renneting of milk is given, based on a first-order breakdown of κ-casein followed by development of instability caused either by a decrease in the intermicellar repulsive potential or by the formation of holes in the stabilizing surface layer of the micelles. Unlike most of the models which have been described, this model allows a complete analytical solution. The solution is, however, complex and difficult to use simply, although it is shown that the calculations are in accord with experimental observations of the dependence of the coagulation process upon the enzyme concentration and the concentration of the milk. The calculations are also compared with those from other models of the reaction.

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Leverant, Calen J., Chad W. Priest, Jeffery A. Greathouse, Mark K. Kinnan, and Susan B. Rempe. "Quantum Calculations of VX Ammonolysis and Hydrolysis Pathways via Hydrated Lithium Nitride." International Journal of Molecular Sciences 22, no. 16 (August 11, 2021): 8653. http://dx.doi.org/10.3390/ijms22168653.

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Recently, lithium nitride (Li3N) has been proposed as a chemical warfare agent (CWA) neutralization reagent for its ability to produce nucleophilic ammonia molecules and hydroxide ions in aqueous solution. Quantum chemical calculations can provide insight into the Li3N neutralization process that has been studied experimentally. Here, we calculate reaction-free energies associated with the Li3N-based neutralization of the CWA VX using quantum chemical density functional theory and ab initio methods. We find that alkaline hydrolysis is more favorable to either ammonolysis or neutral hydrolysis for initial P-S and P-O bond cleavages. Reaction-free energies of subsequent reactions are calculated to determine the full reaction pathway. Notably, products predicted from favorable reactions have been identified in previous experiments.

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Harissopulos, Sotirios, Eleni Vagena, Michail Axiotis, Artemis Spyrou, Georgios Provatas, Anastasios Lagoyannis, Paraskevi Dimitriou, and Hans Werner Becker. "Capture reaction cross-section measurements relevant to p process: the case of (α , γ) reactions on 63Cu, 72Ge,118Sn and the 107Ag(ρ, γ)108Cd reaction." EPJ Web of Conferences 227 (2020): 01008. http://dx.doi.org/10.1051/epjconf/202022701008.

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The cross sections of the 72Ge( α , γ)76Se and 1°7Ag(ρ, γ)1°8Cd reactions were measured at energies relevant to p-process nucleosynthesis. The new data, together with cross section results from our previous ( α , γ) measure-ments on 65Cu and 118Sn and other ( α , γ) cross-section data reported in lit-erature are compared with statistical model calculations performed using the latest version (1.9) of the statistical model code TALYS. In addition, the effect on these calculations of different combinations of the optical model potentials (OMPs), nuclear level densities (NLDs) and γ-ray strength functions (γSFs) entering the calculations was investigated.

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Liao, Kang, Shirong Wang, Wei Li, and Shuhua Li. "Generalized energy-based fragmentation approach for calculations of solvation energies of large systems." Physical Chemistry Chemical Physics 23, no. 35 (2021): 19394–401. http://dx.doi.org/10.1039/d1cp02814f.

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Menzl, Georg, Andreas Singraber, and Christoph Dellago. "S-shooting: a Bennett–Chandler-like method for the computation of rate constants from committor trajectories." Faraday Discussions 195 (2016): 345–64. http://dx.doi.org/10.1039/c6fd00124f.

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Mechanisms of rare transitions between long-lived stable states are often analyzed in terms of commitment probabilities, determined from swarms of short molecular dynamics trajectories. Here, we present a computer simulation method to determine rate constants from such short trajectories combined with free energy calculations. The method, akin to the Bennett–Chandler approach for the calculation of reaction rate constants, requires the definition of a valid reaction coordinate and can be applied to both under- and overdamped dynamics. We verify the correctness of the algorithm using a one-dimensional random walker in a double-well potential and demonstrate its applicability to complex transitions in condensed systems by calculating cavitation rates for water at negative pressures.

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Donskoy, Igor. "Numerical estimation of the thermal stability boundaries for the process of thermochemical conversion processes of biomass in quasi-equilibrium approximation." E3S Web of Conferences 289 (2021): 06001. http://dx.doi.org/10.1051/e3sconf/202128906001.

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The stationary process of pyrolysis and gasification of plant biomass in a wide range of conditions is considered. The reaction rate in a multicomponent system is a complex function of composition and temperature. To simplify the calculations, we use the approximation of the brutto-reaction: it is supposed that a slow reaction of thermal decomposition of biomass proceeds in the reaction zone with first order kinetics and Arrhenius dependence on temperature. Gas phase reactions rates are considered to be high enough to apply the quasi-equilibrium approximation. Calculations make it possible to estimate the temperature values at the boundary of thermal stability and the position of this boundary for different residence times of biofuel in the reaction zone.

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IWATA, YORITAKA, NAOYUKI ITAGAKI, JOACHIM A. MARUHN, and TAKAHARU OTSUKA. "THE COMPETITIVE REACTION MECHANISM IN EXOTIC NUCLEAR REACTIONS." International Journal of Modern Physics E 17, no. 09 (October 2008): 1660–68. http://dx.doi.org/10.1142/s0218301308010672.

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Two principal reaction dynamics are introduced. One is the spin displacement, which is caused from the spin-dependence of the interaction, and the other is the isovector displacement, which is caused from the isospin-dependence of it. The competition of these two dynamics is a rather important factor as the target or projectile has more excess neutrons or protons. In this paper the competitive reaction mechanism is theoretically formulated, where the time-dependent mean field calculations are performed for justification.

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47

Strohmaier, Brigitte. "Reaction-model calculations of cross sections for neutron-induced reactions on 23Na." Annals of Nuclear Energy 20, no. 8 (August 1993): 533–45. http://dx.doi.org/10.1016/0306-4549(93)90002-7.

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48

Wang, Sun, Sun, and Liang. "Chemical Kinetics of Hydrogen Atom Abstraction from Propargyl Sites by Hydrogen and Hydroxy Radicals." International Journal of Molecular Sciences 20, no. 13 (June 30, 2019): 3227. http://dx.doi.org/10.3390/ijms20133227.

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Hydrogen atom abstraction from propargyl C-H sites of alkynes plays a critical role in determining the reactivity of alkyne molecules and understanding the formation of soot precursors. This work reports a systematic theoretical study on the reaction mechanisms and rate constants for hydrogen abstraction reactions by hydrogen and hydroxy radicals from a series of alkyne molecules with different structural propargyl C-H atoms. Geometry optimizations and frequency calculations for all species are performed at M06-2X/cc-pVTZ level of theory and the hindered internal rotations are also treated at this level. The high-level W1BD and CCSD(T)/CBS theoretical calculations are used as a benchmark for a series of DFT calculations toward the selection of accurate DFT functionals for large reaction systems in this work. Based on the quantum chemistry calculations, rate constants are computed using the canonical transition state theory with tunneling correction and the treatment of internal rotations. The effects of the structure and reaction site on the energy barriers and rate constants are examined systematically. To the best of our knowledge, this work provides the first systematic study for one of the key initiation abstraction reactions for compounds containing propargyl hydrogen atoms.

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ANCHISHKIN, D., V. VOVCHENKO, and S. YEZHOV. "HADRONIC REACTION ZONES IN RELATIVISTIC NUCLEUS–NUCLEUS COLLISIONS." International Journal of Modern Physics E 22, no. 06 (June 2013): 1350042. http://dx.doi.org/10.1142/s0218301313500420.

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On the basis of the proposed algorithm for calculation of the hadron reaction rates, the space-time structure of the relativistic nucleus–nucleus collisions is studied. The reaction zones and the reaction frequencies for various types of reactions are calculated for Alternating Gradient Synchrotron (AGS) and Super Proton Synchrotron (SPS) energies within the microscopic transport model. The relation of the reaction zones to the kinetic and chemical freeze-out processes is discussed. It is shown that the space-time freeze-out layer is most extended in time in the central region, while, especially for higher collision energies, the layer becomes very narrow at the sides. The parametrization of freeze-out hypersurface in the form of specific hyperbola of constant proper time was confirmed. The specific characteristic time moments of the fireball evolution are introduced. It is found that the time of the division of a reaction zone into two separate parts does not depend on the collision energy. Calculations of the hadronic reaction frequency show that the evolution of nucleus–nucleus collision can be divided into two hadronic stages.

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Gosavi, Ratnakar K., Imre Safarik, and Otto P. Strausz. "Molecular orbital studies of carbyne reactions: addition and insertion reaction paths for the reaction." Canadian Journal of Chemistry 63, no. 7 (July 1, 1985): 1689–93. http://dx.doi.org/10.1139/v85-283.

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Potential energy hypersurfaces have been studied for the [Formula: see text] addition and insertion reactions by abinitio molecular orbital theory. 6-31G basis set was used for complete geometry optimization of CH, C2H4, the cyclopropyl and allyl radicals as well as the reaction intermediates involved, with the RHF open shell SCF method. CI calculations were then performed at the SCF level optimized geometry. Analysis of the potential energy hypersurfaces predicts, in agreement with reported experimental data, a zero activation energy for the addition reaction via a non least motion, asymmetric reaction path, while the insertion reaction features a computed activation energy of 15 kcal mol−1.

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Journal articles on the topic 'Reaction calculations'

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