Journal articles: 'LCAO (Linear combination of Atomic Orbitals)'

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Custodio, Rogério, and Nelson Henrique Morgon. "Método LCAO." Revista Chemkeys, no. 3 (September 17, 2018): 1–8. http://dx.doi.org/10.20396/chemkeys.v0i3.9639.

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Orbitais atômicos e moleculares podem ser obtidos como uma combinação linear de funções de base. Este modelo ficou conhecido como método da combinação linear de orbitais atômicos (do inglês: Linear Combination of Atomic Orbitals), sendo uma das técnicas mais utilizadas para o cálculo de propriedades eletrônicas de átomos, moléculas, etc., por métodos quânticos. Neste texto serão abordados alguns dos aspectos fundamentais para o cálculo de propriedades eletrônicas através do método denominado Hartree-Fock-Roothaan, que corresponde à aplicação da combinação linear de orbitais atômicos usando o modelo Hartree-Fock.

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Nakhaee, M., M. Yagmurcukardes, S. A. Ketabi, and F. M. Peeters. "Single-layer structures of a100- and b010-Gallenene: a tight-binding approach." Physical Chemistry Chemical Physics 21, no. 28 (2019): 15798–804. http://dx.doi.org/10.1039/c9cp02515d.

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Using the simplified linear combination of atomic orbitals (LCAO) method in combination with ab initio calculations, we construct a tight-binding (TB) model for two different crystal structures of monolayer gallium: a₁₀₀- and b₀₁₀-Gallenene.

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MISHONOV, T. M., J. P. WALLINGTON, E. S. PENEV, and J. O. INDEKEU. "REDUCED PAIRING HAMILTONIAN FOR INTERATOMIC TWO-ELECTRON EXCHANGE IN LAYERED CUPRATES." Modern Physics Letters B 16, no. 19 (August 20, 2002): 693–99. http://dx.doi.org/10.1142/s0217984902004160.

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A detailed Linear Combination of Atomic Orbitals (LCAO) tight-binding model is developed for the layered High-Temperature Superconductor (HTSC) cuprates. The band structure of these materials is described using a σ-band Hamiltonian employing Cu 4s, Cu 3dx2 - y2, O 2px and O 2py atomic orbitals. The Fermi level and the shape of the resulting Fermi surface are fitted to recent Angle Resolved Photon Emission Spectroscopy (ARPES) data to realistically determine the dispersion in the conduction band. Electron-electron interactions and, ultimately, Cooper pairing are obtained by introducing a Heitler–London, two-electron exchange between adjacent orbitals within the CuO 2 plane. Finally, using the LCAO wavefunctions determined by the band structure fit, the Bardeen–Cooper–Schrieffer (BCS) type kernel is derived for interatomic exchange.

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Weng, Xudong, O. F. Sankey, and Peter Rez. "Ab initio band theory approach to electron energy loss near edge structures." Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 506–7. http://dx.doi.org/10.1017/s0424820100104595.

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Single electron band structure techniques have been applied successfully to the interpretation of the near edge structures of metals and other materials. Among various band theories, the linear combination of atomic orbital (LCAO) method is especially simple and interpretable. The commonly used empirical LCAO method is mainly an interpolation method, where the energies and wave functions of atomic orbitals are adjusted in order to fit experimental or more accurately determined electron states. To achieve better accuracy, the size of calculation has to be expanded, for example, to include excited states and more-distant-neighboring atoms. This tends to sacrifice the simplicity and interpretability of the method.In this paper. we adopt an ab initio scheme which incorporates the conceptual advantage of the LCAO method with the accuracy of ab initio pseudopotential calculations. The so called pscudo-atomic-orbitals (PAO's), computed from a free atom within the local-density approximation and the pseudopotential approximation, are used as the basis of expansion, replacing the usually very large set of plane waves in the conventional pseudopotential method. These PAO's however, do not consist of a rigorously complete set of orthonormal states.

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Mantela, Marilena, Constantinos Simserides, and Rosa Di Felice. "LCAO Electronic Structure of Nucleic Acid Bases and Other Heterocycles and Transfer Integrals in B-DNA, Including Structural Variability." Materials 14, no. 17 (August 30, 2021): 4930. http://dx.doi.org/10.3390/ma14174930.

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To describe the molecular electronic structure of nucleic acid bases and other heterocycles, we employ the Linear Combination of Atomic Orbitals (LCAO) method, considering the molecular wave function as a linear combination of all valence orbitals, i.e., 2s, 2px, 2py, 2pz orbitals for C, N, and O atoms and 1s orbital for H atoms. Regarding the diagonal matrix elements (also known as on-site energies), we introduce a novel parameterization. For the non-diagonal matrix elements referring to neighboring atoms, we employ the Slater–Koster two-center interaction transfer integrals. We use Harrison-type expressions with factors slightly modified relative to the original. We compare our LCAO predictions for the ionization and excitation energies of heterocycles with those obtained from Ionization Potential Equation of Motion Coupled Cluster with Singles and Doubles (IP-EOMCCSD)/aug-cc-pVDZ level of theory and Completely Normalized Equation of Motion Coupled Cluster with Singles, Doubles, and non-iterative Triples (CR-EOMCCSD(T))/aug-cc-pVDZ level of theory, respectively, (vertical values), as well as with available experimental data. Similarly, we calculate the transfer integrals between subsequent base pairs, to be used for a Tight-Binding (TB) wire model description of charge transfer and transport along ideal or deformed B-DNA. Taking into account all valence orbitals, we are in the position to treat deflection from the planar geometry, e.g., DNA structural variability, a task impossible for the plane Hückel approach (i.e., using only 2pz orbitals). We show the effects of structural deformations utilizing a 20mer evolved by Molecular Dynamics.

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Kaledin, Alexey L., Craig L. Hill, Tianquan Lian, and Djamaladdin G. Musaev. "A bulk adjusted linear combination of atomic orbitals (BA-LCAO) approach for nanoparticles." Journal of Computational Chemistry 40, no. 1 (October 3, 2018): 212–21. http://dx.doi.org/10.1002/jcc.25373.

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Hamouda, Samir Ahmed. "Gamma-Ray Compton Spectroscopy for Determination of Electron Momentum Distributions in Iron." Advanced Materials Research 815 (October 2013): 8–12. http://dx.doi.org/10.4028/www.scientific.net/amr.815.8.

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Compton profile measurement of iron polycrystalline sample has been performed with 662 keV γ-radiation from a caesium-137 source. The spectrometer calibration and data corrections for the high energy experiment are discussed. The data are compared with the augmented-plane-wave (APW) and linear combination of atomic orbitals (LCAO) band theoretical Compton profiles of iron. Both theoretical predictions show the band theories overestimate the momentum density at low momenta and underestimate it at intermediate momenta.

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Craig, BL, and PV Smith. "Parametrisation of the LCAO Bandstructure of BCC Transition Metals." Australian Journal of Physics 41, no. 6 (1988): 797. http://dx.doi.org/10.1071/ph880797.

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In this paper we present a direct parameter fitting scheme appropriate to a linear combination of atomic orbitals (LCAO) model� Hamiltonian representation of the BCC transition metals incorporating first and second neighbour interactions. Explicit expressions are given for the one-electron eigenvalues at all of the important symmetry points of the BCC Brillouin zone. This direct parameter fitting scheme is shown to produce an excellent representation of the bandstructure of paramagnetic iron, and yields parameter values little different from those obtained from a full least-squares optimisation of the LCAO model Hamiltonian bandstructure. The extension of this scheme to include more distant interactions, and relativistic and spin-orbit effects, is also discussed.

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Biczó, G. "On the self-consistent-field linear combination of atomic orbitals for bounded crystal orbitals (SCF-LCAO-BCO) method." Journal of Molecular Structure: THEOCHEM 188, no. 3-4 (August 1989): 429–39. http://dx.doi.org/10.1016/0166-1280(89)85125-5.

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Masuda-Jindo, K., V. K. Tewary, and Robb Thomson. "Atomic theory of fracture of brittle materials: Application to covalent semiconductors." Journal of Materials Research 6, no. 7 (July 1991): 1553–66. http://dx.doi.org/10.1557/jmr.1991.1553.

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Using the lattice Green's function approach and LCAO (linear combination of atomic orbitals) electron theory, we investigate the atomistic configuration and lattice trapping of cracks in Si. The LCAO electron theory coupled to second order perturbation theory (SOP) has been used to derive explicit expressions for the bond breaking nonlinear forces between Si atoms. We calculate the cracked lattice Green's functions for a crack on the (111) plane and lying in the (110) direction. With the nonlinear forces acting in a cohesive region near the crack tips, the crack structure is then calculated. The calculated structure possesses a crack opening at the Griffith load which should allow penetration of typical external molecules to the crack tip at the Griffith loading. Other consequences for chemical reactions at the crack tip are discussed in the light of these results. The lattice trapping is low, only a few percent of the Griffith load.

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Journal, Baghdad Science. "Electronic Structure of Copper Antimony Using Compton Scattering Technique." Baghdad Science Journal 13, no. 1 (December 30, 2018): 167–73. http://dx.doi.org/10.21123/bsj.13.1.167-173.

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In this paper we present the first ever measured experimental electron momentum density of Cu2Sb at an intermediate resolution (0.6 a.u.) using 59.54 keV 241Am Compton spectrometer. The measurements are compared with the theoretical Compton profiles using density function theory (DFT) within a linear combination of an atomic orbitals (LCAO) method. In DFT calculation, Perdew-Burke-Ernzerhof (PBE) scheme is employed to treat correlation whereas exchange is included by following the Becke scheme. It is seen that various approximations within LCAO-DFT show relatively better agreement with the experimental Compton data. Ionic model calculations for a number of configurations (Cu+x/2)2(Sb-x) (0.0≤x≤2.0) are also performed utilizing free atom profiles, the ionic model suggests transfer of 2.0 electrons per Cu atom from 4s state to 5p state of Sb.

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Koch, Wolfhard, Bastian Frey, Juan Francisco Sánchez Ruiza, and Thomas Scior. "On Rüdenberg’s Integral Approximations and Their Unrestricted and Combined Use in Crystal Orbital Theories of Hartree-Fock Type." Zeitschrift für Naturforschung A 58, no. 12 (December 1, 2003): 785–800. http://dx.doi.org/10.1515/zna-2003-1213.

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The analysis based on Rüdenberg’s well-known letter of 1951, which has been outlined for molecules in a preceding contribution, now will be transfered to translational periodic systems in one, two, or three dimensions. Again, when applied unrestrictedly to “Linear Combination of Atomic Orbitals” representations (LCAO) of both “Unrestricted” and “Restricted Hartree-Fock” pictures (UHF and RHF), Rüdenberg’s integral approximations of Mulliken type lead to a thorough interpretation of “Extended Hückel” crystal orbital theories (EHT). Moreover, Rüdenberg’s ideas provide us with “Unrestricted and Combined” extensions (U&C) of the widely-used approximation schemes “Zero Differential Overlap” (ZDO) and “Neglect of Diatomic Differential Overlap” (NDDO). An improved variant of EHT is also presented. Corresponding “Restricted and Combined” concepts (R&C), which overcome some shortcomings inherent in Rüdenberg’s original recipes, will be sketched.

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Корабельников, Д. В. "Колебательные и тепловые свойства оксианионных кристаллов." Физика твердого тела 60, no. 3 (2018): 565. http://dx.doi.org/10.21883/ftt.2018.03.45563.216.

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AbstractThe vibrational and thermal properties of dolomite and alkali chlorates and perchlorates were studied in the gradient approximation of density functional theory using the method of a linear combination of atomic orbitals (LCAO). Long-wave vibration frequencies, IR and Raman spectra, and mode Gruneisen parameters were calculated. Equation-of-state parameters, thermodynamic potentials, entropy, heat capacity, and thermal expansion coefficient were also determined. The thermal expansion coefficient of dolomite was established to be much lower than for chlorates and perchlorates. The temperature dependence of the heat capacity at T > 200 K was shown to be generally governed by intramolecular vibrations.

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Bhambhani, P., K. Kabra, B. K. Sharma, and G. Sharma. "High Pressure Study of Structural and Electronic Properties of PbSe." Journal of Solid State Physics 2014 (December 30, 2014): 1–7. http://dx.doi.org/10.1155/2014/921092.

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High pressure structural phase transition and electronic properties have been investigated using the linear combination of atomic orbitals (LCAO) method with two exchange-correlation approximations, the generalized gradient approximation (GGA) and local density approximation (LDA). The present study shows phase transitions from B1 to B27 and B27 to B2 at 6.24 GPa and 16.39 GPa, respectively. Lattice constant, bulk modulus, and energy gap of pressure-induced PbSe are found to be in good agreement with previous theoretical and experimental results. Variation of electronic band structure with pressure shows direct band gap along L point of the Brillouin zone.

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BERLU, LILIAN, and HASSAN SAFOUHI. "ANALYTICAL DEVELOPMENT OF MULTICENTER OVERLAP-LIKE QUANTUM SIMILARITY INTEGRALS OVER SLATER TYPE ORBITALS AND NUMERICAL EVALUATION." Journal of Theoretical and Computational Chemistry 04, no. 03 (September 2005): 787–801. http://dx.doi.org/10.1142/s0219633605001866.

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Molecular overlap-like quantum similarity measurements imply the evaluation of overlap integrals of two molecular electronic densities related by the Dirac delta function. When the electronic densities are expanded over atomic orbitals using the usual LCAO (Linear Combination of Atomic Orbitals) scheme, overlap-like quantum similarity integrals could be expressed as a linear combination of four-center overlap integrals. In previous works, we showed that the one-center two-range expansion method leads to very complicated analytic expressions for three- and four-center terms. This is why its use has been prevented even for two-center integrals. We also showed that the use of the Fourier transform approach, combined with the so-called B functions, leads to great simplifications in both analytical and numerical development of overlap-like quantum similarity integrals over Slater type functions. In this work, a unified analytical treatment of multicenter overlap-like quantum similarity integrals over Slater type functions is described. The Fourier transform and nonlinear transformation methods are used. The numerical results section shows that the approach described in the present work can be applied to two-, three- and four-center integrals whatever nucleus positions might be.

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Ahuja, Babu Lal, and Narayan Lal Heda. "Use of a Lowest Intensity 241Am Compton Spectrometer for the Measurement of Directional Compton Profiles of ZnSe." Zeitschrift für Naturforschung A 61, no. 7-8 (August 1, 2006): 364–70. http://dx.doi.org/10.1515/zna-2006-7-809.

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In this paper we report on electron momentum densities in ZnSe using Compton scattering technique. For the directional measurements we have employed a newly developed 100 mCi 241Am Compton spectrometer which is based on a small disc source with shortest geometry. For the theoretical calculations we have employed a self-consistent Hartree-Fock linear combination of atomic orbitals (HF-LCAO) approach. It is seen that the anisotropy in the measured Compton profiles is well reproduced by our HF-LCAOcalculation and the other available pseudopotential data. The anisotropy in the Compton profiles is explained in terms of energy bands and bond length. - PACS numbers: 13.60.Fz, 78.70. Ck, 78.70.-g

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Piskunov, Sergei, Aleksejs Gopejenko, Vladimir Pankratov, Inta Isakoviča, Chong-Geng Ma, Mikhail G. Brik, Michal Piasecki, and Anatoli I. Popov. "First Principles Calculations of Atomic and Electronic Structure of TiAl3+- and TiAl2+-Doped YAlO3." Materials 14, no. 19 (September 26, 2021): 5589. http://dx.doi.org/10.3390/ma14195589.

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In this paper, the density functional theory accompanied with linear combination of atomic orbitals (LCAO) method is applied to study the atomic and electronic structure of the Ti3+ and Ti2+ ions substituted for the host Al atom in orthorhombic Pbnm bulk YAlO3 crystals. The disordered crystalline structure of YAlO3 was modelled in a large supercell containing 160 atoms, allowing simulation of a substitutional dopant with a concentration of about 3%. In the case of the Ti2+-doped YAlO3, compensated F-center (oxygen vacancy with two trapped electrons) is inserted close to the Ti to make the unit cell neutral. Changes of the interatomic distances and angles between the chemical bonds in the defect-containing lattices were analyzed and quantified. The positions of various defect levels in the host band gap were determined.

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Cargnoni, Fausto, and Marco Scavini. "Direct-space analysis of the electronic structure of the YBa2Cu3O6 and YBa2Cu3O7 crystals." Canadian Journal of Chemistry 80, no. 3 (March 1, 2002): 235–44. http://dx.doi.org/10.1139/v02-014.

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The electronic structure of the YBa2Cu3O6 and YBa2Cu3O7 crystals is investigated by means of fully periodic-restricted HartreeFock LCAO (linear combination of atomic orbitals) pseudopotential calculations. To give a detailed description of the bonding and atomic properties of the materials studied we selected the quantum theory of atoms in molecules approach, and complementary information is obtained from the analysis of the electron localization function in specific cell regions. The main features of the YBa2Cu3O6 and YBa2Cu3O7 crystals' electron densities are detailed and compared with available experimental data. Since the superconducting transition requires oxidation of the YBa2Cu3O6 crystal, we focused on the electronic rearrangements related to the inclusion of oxygen. CuO planes, probably responsible for the superconducting transition, exhibit peculiar electronic properties.Key words: superconducting cuprates, electron density, ab initio calculations.

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Ekuma, E. C., L. Franklin, G. L. Zhao, J. T. Wang, and D. Bagayoko. "Local density approximation description of electronic properties of wurtzite cadmium sulfide (w-CdS)." Canadian Journal of Physics 89, no. 3 (March 2011): 319–24. http://dx.doi.org/10.1139/p11-023.

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We present calculated, electronic, and related properties of wurtzite cadmium sulfide (w-CdS). Our ab initio, nonrelativistic calculations employ a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Following the Bagayoko, Zhao, and Williams (BZW) method, we solved self-consistently both the Kohn–Sham equation and the equation giving the ground-state density in terms of the wave functions of the occupied states. Our calculated, direct band gap of 2.47 eV at the Γ point is in excellent agreement with experiment. So are the calculated density of states and the electron effective mass. In particular, our results reproduce the peaks in the conduction band density of states, within experimental uncertainties.

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BELAYADI, A., B. BOURAHLA, and F. MEKIDECHE-CHAFA. "LOCALIZED ELECTRONIC SURFACE STATES IN METALLIC STRUCTURES." Surface Review and Letters 25, no. 05 (July 2018): 1850101. http://dx.doi.org/10.1142/s0218625x18501019.

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We present theoretical models to study the localized electronic surface states in metallic structures. The materials under study have been chosen with different types of cubic meshes, fcc, sc and bcc. The calculation method used is closely related to the Linear Combination of Atomic Orbitals (LCAO) in the tight-binding method. We consider three cases: each of the atoms is described by a single atomic orbital of [Formula: see text]-, [Formula: see text]- and [Formula: see text]-type orbitals. In order to solve the rectangular secular equations of the systems under study, the phase field matching method is involved. In particular, we apply our approach to calculate the localized electronic surface states of some metals: (i) Chromium and Silver having, respectively, bcc and fcc structure and described as [Formula: see text]-type orbital. (ii) Nickel with sc crystallization and described by [Formula: see text]-type orbital. (iii) Palladium (Pd) given in fcc crystallization and described by [Formula: see text]-type orbital. The obtained results illustrate spatial edge effects between the bulk modes and the localized electronic states of the metallic surfaces over the three orientations of high symmetry path. We observe many localized states above and below the bulk band range. In addition, the relaxation effect on the surface layer has been investigated to compute the localized electronic surface state in this case and illustrate the lift of the degeneracy compared to the first calculations based on an ordered surface. The spacing geometry caused by the relaxation on the surface has been determined by using the Molecular dynamic algorithm and Morse interatomic potential.

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Munjal, N., M. C. Mishra, G. Sharma, and B. K. Sharma. "Electron Momentum Density and Phase Transition in ZnS." Journal of Theoretical Chemistry 2013 (June 20, 2013): 1–7. http://dx.doi.org/10.1155/2013/349870.

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The electron momentum density distribution and phase transition in ZnS are reported in this paper. The calculations are performed on the basis of density functional theory (DFT) based on the linear combination of atomic orbitals (LCAO) method. To compare the theoretical Compton profile, the measurement on polycrystalline ZnS has been made using a Compton spectrometer employing 59.54 keV gamma rays. The spherically averaged theoretical Compton profile is in agreement with the measurement. On the basis of equal valence-electron-density Compton profiles, it is found that ZnS is less covalent as compared to ZnSe. The present study suggests zincblende (ZB) to rocksalt (RS) phase transition at 13.7 GPa. The calculated transition pressure is found in good agreement with the previous investigations.

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Stewart, Anthony Duane. "Ab-initio Calculations of Electronic, Transport, and Bulk Properties of cubic Boron Nitride (zb-BN)." JOURNAL OF ADVANCES IN PHYSICS 9, no. 1 (June 4, 2015): 2277–86. http://dx.doi.org/10.24297/jap.v9i1.1463.

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We present results from ab-initio, self consistent, local density approximation (LDA) calculations of electronic and related properties of cubic boron nitride (zb-BN).Â We employed the Ceperley and Alder LDA potential and the linear combination of atomic orbitals (LCAO) formalism in our non-relativistic computations.Â We solved the system of LDA equations self-consistently, through the implementation of the LCAO formalism, following the Bagayoko, Zhao, and Williams (BZW) method as enhanced by Ekuma and Franklin (BZW-EF).Â The BZW-EF method includes a methodical search for the optimal basis set that yields the absolute minima of the occupied energies.Â This search entails increasing the size of the basis set and the related modifications of angular symmetry and of radial orbitals.Â Our calculated, indirect band gap of 6.48 eV, from the Î“ to the Î§ points, and bulk modulus of 375 GPa are in excellent agreement with corresponding experimental values at room temperature (RT).Â The calculated widths of the lowest valance band and that of the entire valence bands of 5.65 eV and 20.26 eV are in excellent agreement with the measured values of 5.5 eV and 20 eV, respectively.Â We have also calculated electron and hole effective masses for zb-BN, and the total (DOS) and partial (pDOS) densities of states. Â Â

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MAHDAVI, M., B. KALEJI, and T. KOOHROKHI. "FUSION RATE IN μtt IN MUONIC MOLECULAR ION USING LINEAR COMBINATION OF ATOMIC ORBITAL METHOD." International Journal of Modern Physics E 20, no. 03 (March 2011): 629–36. http://dx.doi.org/10.1142/s0218301311018113.

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In this paper, the tritium–tritium fusion reaction rate in a muonic molecular ion (μtt) is calculated by using a square-well nuclear potential as a complex for nuclear interaction between two tritones. The complex potential parameters are obtained by fitting process on fusion cross-section experimental data. The real and imaginary parts of the nuclear potential are calculated as Ur = -62531.87 (keV) and Ui = -165.63 (keV), respectively. A free parameter that is related to the radius of this potential is A = 0.004155. Also, considering the optical nuclear potential, the energy value of μtt muonic molecular ion is calculated. The fusion rate is calculated by liner combination of atomic orbital (LCAO) method. Finally, the reaction rate, λ, is obtained 0.28×1010 s -1 by calculating the transition probability through the potential barrier and the oscillation frequency of wave function.

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Barklem, P. S. "Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen." Astronomy & Astrophysics 610 (February 2018): A57. http://dx.doi.org/10.1051/0004-6361/201731968.

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Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000–20 000 K, and charge transfer and (de)excitation processes involving the first excited S-states, 4s.5So and 4s.3So, are found to have the highest rates.

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MALOZOVSKY, Y., L. FRANKLIN, E. C. EKUMA, G. L. ZHAO, and D. BAGAYOKO. "AB-INITIO CALCULATIONS OF ELECTRONIC PROPERTIES OF InP AND GaP." International Journal of Modern Physics B 27, no. 15 (June 4, 2013): 1362013. http://dx.doi.org/10.1142/s0217979213620130.

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We present results from ab-initio, self-consistent local density approximation (LDA) calculations of electronic and related properties of zinc blende indium phosphide (InP) and gallium phosphide (GaP) . We employed a LDA potential and implemented the linear combination of atomic orbitals (LCAO) formalism. This implementation followed the Bagayoko, Zhao and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW–EF). This method searches for the optimal basis set that yields the minima of the occupied energies. This search entails increases of the size of the basis set and the related modifications of angular symmetry and of radial orbitals. Our calculated, direct band gap of 1.398 eV (1.40 eV), at the Γ point, is in excellent agreement with experimental values, for InP , and our preliminary result for the indirect gap of GaP is 2.135 eV, from the Γ to X high symmetry points. We have also calculated electron and hole effective masses for both InP and GaP . These calculated properties also agree with experimental findings. We conclude that the BZW–EF method could be employed in calculations of electronic properties of high-Tc superconducting materials to explain their complex properties.

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Amarsi, A. M., and P. S. Barklem. "Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen." Astronomy & Astrophysics 625 (May 2019): A78. http://dx.doi.org/10.1051/0004-6361/201935101.

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Low-energy inelastic collisions with neutral hydrogen atoms are important processes in stellar atmospheres, and a persistent source of uncertainty in non-LTE modelling of stellar spectra. We have calculated and studied excitation and charge transfer of C I and of N I due to such collisions. We used a previously presented method that is based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions for the adiabatic potential energies, combined with the multichannel Landau-Zener model for the collision dynamics. We find that charge transfer processes typically lead to much larger rate coefficients than excitation processes do, consistent with studies of other atomic species. Two-electron processes were considered and lead to non-zero rate coefficients that can potentially impact statistical equilibrium calculations. However, they were included in the model in an approximate way, via an estimate for the two-electron coupling that was presented earlier in the literature: the validity of these data should be checked in a future work.

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Bhandari, Uttam, Blaise Awola Ayirizia, Yuriy Malozovsky, Lashounda Franklin, and Diola Bagayoko. "First Principle Investigation of Electronic, Transport, and Bulk Properties of Zinc-Blende Magnesium Sulfide." Electronics 9, no. 11 (October 29, 2020): 1791. http://dx.doi.org/10.3390/electronics9111791.

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We have studied electronic, structural, and transport properties of zinc-blende magnesium sulfide (zb-MgS). We employed a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) method. Our computational method is able to reach the ground state of a material, as dictated by the second theorem of density functional theory (DFT). Consequently, our findings have the physical content of DFT and agree with available, corresponding experimental ones. The calculated band gap of zb-MgS, a direct gap equal to 4.43 eV, obtained at the experimental lattice constant of 5.620 Å, completely agrees with the experimental band gap of 4.45 ± 0.2 eV. We also report total (DOS) and partial (pDOS) densities of states, electron and hole effective masses, the equilibrium lattice constant, and the bulk modulus. The calculated pDOS also agree with the experiment for the description of the states at the top and the bottom of the valence and conduction bands, respectively.

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Dash, Debashish, Chandan Kumar Pandey, Saurabh Chaudhary, and Susanta Kumar Tripathy. "Structural, electronic, and mechanical properties of anatase titanium dioxide." Multidiscipline Modeling in Materials and Structures 15, no. 2 (February 21, 2019): 306–16. http://dx.doi.org/10.1108/mmms-03-2018-0043.

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PurposeThe purpose of this paper is to analyze various properties of anatase titanium dioxide (TiO2) nanoparticles. Further, it proposes to implement Linear Combinations of Atomic Orbitals (LCAO) basis set under the framework of density functional theory and outline how LCAO is able to provide improved results in terms of various mechanical properties rather than plane wave and other theoretical results.Design/methodology/approachThis paper provides an exploratory study on anatase TiO2by implementing OLCAO–DFT–LDA–LBFGS–EOS–PZ algorithms to find out various ground-level properties. The data so obtained are complemented by various analysis using mathematical expressions, description of internal processes occurred and comparison to others’ analytical results.FindingsThe paper provides some empirical insights on how mechanical properties of anatase TiO2improved by implementing LCAO methodology. From the analysis of electronic properties, it is seen that the anatase TiO2supports the inter band indirect transition from O-2p in valence region to Ti-3d in the conduction region.Research limitations/implicationsMost of the electronic properties are underestimated because a single exchange-correlation potential is not continuous across the gap. This gap can be enhanced by implementing Green’s function in place of DFT and the other way is to implement self-interaction correction.Practical implicationsThe use of anatase TiO2is primarily used for catalytic applications. This is also used to enhance the quality of paper in the paper industry. Additionally, this is used as a prime ingredient in cosmetic industry.Originality/valueThis paper fulfills an identified need to study how LCAO, another basis set, plays an important role in improving material properties.

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Prazyan, Tigran L., and Yuri N. Zhuravlev. "Ab initio study of naphthalene and anthracene elastic properties." International Journal of Modern Physics C 29, no. 03 (March 2018): 1850024. http://dx.doi.org/10.1142/s0129183118500249.

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A study of the crystal structure, mechanical and acoustic properties of two [Formula: see text] and [Formula: see text] monoclinic phases of naphthalene and anthracene was performed using ab initio method of linear combination of atomic orbitals (LCAO) and basis sets: C_6-21G*, H_3-1p1G. The method was implemented in the CRYSTAL[Formula: see text]14,[Formula: see text]17 software package using electron density functional theory including van der Waals interactions (DFT-D2 and DFT-D3 (BJ)), in the local density approximation (LDA) with VWN exchange-correlation potential, gradient approximation PBE exchange-correlation functional and B3LYP hybrid functional. The calculated elastic constants for the first time are in moderate agreement with experimental data. Bulk modulus [Formula: see text], shear modulus [Formula: see text], Young’s modulus [Formula: see text] and the Poisson’s ratio [Formula: see text], as well as acoustic properties (average velocity of sound [Formula: see text], the Debye temperature [Formula: see text], and acoustic Grüneisen parameter [Formula: see text]) were obtained using the Voigt–Reuss–Hill model.

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JAVAN, MASOUD BEZI. "ELECTRONIC AND OPTICAL PROPERTIES OF NITROGEN DOPED SiC NANOCRYSTALS: FIRST PRINCIPLES STUDY." International Journal of Modern Physics B 27, no. 13 (May 15, 2013): 1350053. http://dx.doi.org/10.1142/s0217979213500537.

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A typical nitrogen doped spherical SiC nanocrystal with a diameter of 1.2 nm ( Si 43 C 44 H 76) using linear combination atomic orbital (LCAO) in combination with pseudopotential density functional calculation have been studied. Our selected SiC nanocrystal has been modeled taking all the cubic bulk SiC atoms contained within a sphere of a given radius and terminating the surface dangling bonds with hydrogen atoms. We have examined nine possible situations in which nitrogen has a high probability for replacement in the lattice or placed between atoms in the nanocrystal. We have found that the silicone can substitute with a nitrogen atom in each layer as the constructed nanocrystals remain thermodynamically stable. Also the nitrogen atom can be placed between the free atomic spaces as the more thermodynamically stable position of the nitrogen is between the topmost layers. Also the optical absorption and refractive index energy dispersions of the pure and various stable doped SiC nanocrystals were studied.

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Byzova, E. S., and D. V. Korabel’nikov. "The Effect of Pressure on the Structure and Electronic Properties of Hydrated Calcium Carbonates." Izvestiya of Altai State University, no. 4(114) (September 9, 2020): 33–38. http://dx.doi.org/10.14258/izvasu(2020)4-05.

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This paper studies the effect of pressure on the structure and electronic properties of CaCO3-H2O and CaCO3-6H2O crystalline hydrates. The study is based on the density functional theory (DFT) and the linear combination of atomic orbitals (LCAO) method. Calculations are performed using the CRYSTAL17 software package and the PBE gradient functional. The calculated lattice parameters of hydrated calcium carbonates and their dependence on external hydrostatic pressure are shown to be in good agreement with the available experimental measurements. Dependencies of linear compressibility on the direction are obtained using the calculated pressure dependencies of the structural parameters. It is demonstrated that the linear compressibility of calcium carbonate hexahydrate, in contrast to calcium carbonate monohydrate, is highly anisotropic (the smallest and largest compressibility values are correlated as K max /K min ~ 4). In this case, the maximum compressibility is located between crystallographic axes (between the axes a and c) and not along the crystallographic axes. The bulk modulus for the monohydrate (CaCO3-6H2O) is greater than for the hexahydrate (CaCO3-6H2O). Total and partial densities of electronic states for CaCO3-H2O and CaCO3-6H2O are calculated. Also, dependencies of the band gap width on pressure for hydrated calcium carbonates are established. It is shown that, with increasing pressure, the increase of the band gap is greater for CaCO3-6H2O than for CaCO3-H2O.

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32

Cossard, Alessandro, Silvia Casassa, Carlo Gatti, Jacques K. Desmarais, and Alessandro Erba. "Topology of the Electron Density and of Its Laplacian from Periodic LCAO Calculations on f-Electron Materials: The Case of Cesium Uranyl Chloride." Molecules 26, no. 14 (July 12, 2021): 4227. http://dx.doi.org/10.3390/molecules26144227.

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The chemistry of f-electrons in lanthanide and actinide materials is yet to be fully rationalized. Quantum-mechanical simulations can provide useful complementary insight to that obtained from experiments. The quantum theory of atoms in molecules and crystals (QTAIMAC), through thorough topological analysis of the electron density (often complemented by that of its Laplacian) constitutes a general and robust theoretical framework to analyze chemical bonding features from a computed wave function. Here, we present the extension of the Topond module (previously limited to work in terms of s-, p- and d-type basis functions only) of the Crystal program to f- and g-type basis functions within the linear combination of atomic orbitals (LCAO) approach. This allows for an effective QTAIMAC analysis of chemical bonding of lanthanide and actinide materials. The new implemented algorithms are applied to the analysis of the spatial distribution of the electron density and its Laplacian of the cesium uranyl chloride, Cs2UO2Cl4, crystal. Discrepancies between the present theoretical description of chemical bonding and that obtained from a previously reconstructed electron density by experimental X-ray diffraction are illustrated and discussed.

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33

Malozovsky, Yuriy, Lashounda Franklin, Chinedu Ekuma, and Diola Bagayoko. "Ab initio prediction of electronic, transport and bulk properties of Li2S." International Journal of Modern Physics B 29, no. 25n26 (October 14, 2015): 1542006. http://dx.doi.org/10.1142/s0217979215420060.

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In this paper, we present results from ab initio, self-consistent, local density approximation (LDA) calculations of electronic and related properties of cubic antifluorite (anti-[Formula: see text]) lithium sulfide [Formula: see text]. Our nonrelativistic computations implemented the linear combination of atomic orbital (LCAO) formalism following the Bagayoko, Zhao and Williams method, as enhanced by Ekuma and Franklin (BZW–EF). Consequently, using several self-consistent calculations with increasing basis sets, we searched for the smallest basis set that yields the absolute minima of the occupied energies. The outcomes of the calculation with this basis set, called the optimal basis set, have the full physical content of density functional theory (DFT). Our calculated indirect band gap, from [Formula: see text] to [Formula: see text], is 3.723 eV, for the low temperature experimental lattice constant of 5.689 Å. The predicted indirect band gap of 3.702 eV is obtained for the computationally determined equilibrium lattice constant of 5.651 Å. We have also calculated the total density of states (DOS) and partial densities of states (pDOS), electron and hole effective masses and the bulk modulus of [Formula: see text]. Due to a lack of experimental results, most of the calculated ones reported here are predictions for this material suspected of exhibiting a high temperature superconductivity similar to that of [Formula: see text].

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34

Boujrhal, F. Z., El Kebir Hlil, R. Cherkaoui El Moursli, T. El Khoukhi, and B. Sghir. "A Comparative Study of Radon Retention Ability of Crystalline Apatite and Amorphous Oxide Materials." Materials Science Forum 480-481 (March 2005): 169–74. http://dx.doi.org/10.4028/www.scientific.net/msf.480-481.169.

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Comparative radon investigations of two natural materials, crystalline apatite and amorphous oxide, are presented here. The radon retention in the apatite (sedimentary apatite) is more than 70% of the total radon formed in the solid matrix. The amorphous oxide (gel hydrothermal alteration) retains only 7% of radon. The nature of the material which plays an important role in the radon diffusion is confirmed by heat treatment. The major and interesting result of this heat treatment is increasing of crystallite size. This phenomenon induces improvement on radon retention ability. To study these properties one uses a structure band calculations based on the Linear Combinations of Orbital Atomic (LCAO) method convenient numerically for the ionic systems.

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35

Mitroy, J. "A Hartree - Fock Program for Atomic Structure Calculations." Australian Journal of Physics 52, no. 6 (1999): 973. http://dx.doi.org/10.1071/ph99042.

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The Hartree–Fock equations for a general open shell atom are described. The matrix equations that result when the single particle orbitals are written in terms of a linear combination of analytic basis functions are derived. Attention is paid to the complexities that occur when open shells are present. The specifics of a working FORTRAN program which is available for public use are described. The program has the flexibility to handle either Slater-type orbitals or Gaussian-type orbitals.

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Prayitno, Teguh Budi, and Fumiyuki Ishii. "Implementation of Generalized Bloch Theorem Using Linear Combination of Pseudo-Atomic Orbitals." Journal of the Physical Society of Japan 87, no. 11 (November 15, 2018): 114709. http://dx.doi.org/10.7566/jpsj.87.114709.

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37

Feibelman, Peter J. "Calculation of surface stress in a linear combination of atomic orbitals representation." Physical Review B 50, no. 3 (July 15, 1994): 1908–11. http://dx.doi.org/10.1103/physrevb.50.1908.

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Orner, B. A., and J. Kolodzey. "Si1−x−yGexCy alloy band structures by linear combination of atomic orbitals." Journal of Applied Physics 81, no. 10 (May 15, 1997): 6773–80. http://dx.doi.org/10.1063/1.365220.

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Slavney, Adam H., Bridget A. Connor, Linn Leppert, and Hemamala I. Karunadasa. "A pencil-and-paper method for elucidating halide double perovskite band structures." Chemical Science 10, no. 48 (2019): 11041–53. http://dx.doi.org/10.1039/c9sc03219c.

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Mikajlo, E. A., K. L. Nixon, and M. J. Ford. "Electron momentum spectroscopy and linear combination of atomic orbitals calculation of bulk Na2O." Journal of Physics: Condensed Matter 15, no. 13 (March 24, 2003): 2155–68. http://dx.doi.org/10.1088/0953-8984/15/13/302.

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Joshi, K. B., and B. K. Sharma. "Electronic and structural properties of MgB2 by the linear combination of atomic orbitals method." Journal of Applied Physics 102, no. 10 (November 15, 2007): 103713. http://dx.doi.org/10.1063/1.2811934.

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42

Mokkath, Junais Habeeb. "Localized surface plasmon resonances of a metal nanoring." Physical Chemistry Chemical Physics 22, no. 41 (2020): 23878–85. http://dx.doi.org/10.1039/d0cp04216a.

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Using the linear combination of atomic orbitals real-time-propagation rt-TDDFT technique and transition contribution maps, we study the optical and plasmonic features of a metal nanoring made up of sodium atoms.

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43

Suzuki, Shugo, and Toshihiro Ariizumi. "An Orthogonalized Valence Orbital Approximation in Relativistic Full-Potential Linear-Combination-of-Atomic-Orbitals Methods." Journal of the Physical Society of Japan 76, no. 2 (February 15, 2007): 024707. http://dx.doi.org/10.1143/jpsj.76.024707.

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Uljashin, A. G., A. M. Zaitsev, and H. Ali Noor. "Nitrogen-containing defects in diamond: experimental data and molecular orbital linear-combination-of-atomic-orbitals." Materials Science and Engineering: B 11, no. 1-4 (January 1992): 359–62. http://dx.doi.org/10.1016/0921-5107(92)90241-z.

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Fernández-Seivane, L., M. A. Oliveira, S. Sanvito, and J. Ferrer. "On-site approximation for spin–orbit coupling in linear combination of atomic orbitals density functional methods." Journal of Physics: Condensed Matter 18, no. 34 (August 11, 2006): 7999–8013. http://dx.doi.org/10.1088/0953-8984/18/34/012.

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Fernández-Seivane, F., M. A. Oliveira, S. Sanvito, and J. Ferrer. "On-site approximation for spin–orbit coupling in linear combination of atomic orbitals density functional methods." Journal of Physics: Condensed Matter 19, no. 48 (November 13, 2007): 489001. http://dx.doi.org/10.1088/0953-8984/19/48/489001.

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Gashimzade, F. M., D. G. Guliev, D. A. Guseinova, and V. Y. Shteinshrayber. "Band-structure calculation for A4B6layered crystals by the equivalent-orbital linear combination of atomic orbitals method." Journal of Physics: Condensed Matter 4, no. 4 (January 27, 1992): 1081–91. http://dx.doi.org/10.1088/0953-8984/4/4/018.

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Feibelman, Peter J. "Efficient solution of Poisson’s equation in linear combination of atomic orbitals calculations of crystal electronic structure." Physical Review B 33, no. 2 (January 15, 1986): 719–25. http://dx.doi.org/10.1103/physrevb.33.719.

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Hafner, J., and W. Weber. "Total-energy calculations for intermetallic compounds with a first-principles linear combination of atomic orbitals method." Physical Review B 33, no. 2 (January 15, 1986): 747–54. http://dx.doi.org/10.1103/physrevb.33.747.

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Boettger, J. C., M. D. Jones, and R. C. Albers. "Structural properties of crystalline uranium from linear combination of Gaussian-type orbitals calculations." International Journal of Quantum Chemistry 75, no. 4-5 (1999): 911–15. http://dx.doi.org/10.1002/(sici)1097-461x(1999)75:4/5<911::aid-qua55>3.0.co;2-x.

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Journal articles on the topic 'LCAO (Linear combination of Atomic Orbitals)'

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