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Journal articles on the topic 'RPA [Approximation phase aléatoire]'

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Published: 4 June 2021

Last updated: 6 February 2022

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1

FETTER, A. L., C. B. HANNA, and R. B. LAUGHLIN. "ANYONS AND SUPERCONDUCTIVITY: RANDOM PHASE APPROXIMATION." International Journal of Modern Physics B 05, no. 16n17 (October 1991): 2751–90. http://dx.doi.org/10.1142/s0217979291001097.

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The two-dimensional ideal gas of particles obeying ν fractional statistics is recast as an interacting Fermi gas with long-range gauge potentials. A self-consistent dielectric description of the random phase approximation (RPA) provides a concise expression for the linear response of the fractional statistics gas to an external electromagnetic field. The RPA, believed to be correct for the present case of long-range interactions, yields two central results that are classic features of superconductivity: (1) a sharp undamped collective mode with a linear dispersion relation at long wavelengths: (2) a gauge-invariant Meissner effect in the transverse response to an external magnetic field.

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2

KHVESHCHENKO, D. V., and IAN I. KOGAN. "ANYON SUPERCONDUCTIVITY BEYOND THE RANDOM PHASE APPROXIMATION." International Journal of Modern Physics B 05, no. 14 (August 20, 1991): 2355–83. http://dx.doi.org/10.1142/s0217979291000924.

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We carry out a revision of the mechanism of anyon superconductivity found in the Random Phase Approximation. It is shown that the Debye screening of a statistical Coulomb-like interaction produced by contributions beyond the RPA destroys the abovementioned mechanism. The linear mode appeared in the particle-hole channel within the RPA is identified with a finite damping zero-sound. As an alternative mechanism an attraction of anyons which could lead to a formation of boson composites is observed. A finite temperature phase transition, hydrodynamics and electrodynamics of anyon system are described from this alternative point of view.

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3

DUKELSKY, J., and P. SCHUCK. "VARIATIONAL RANDOM PHASE APPROXIMATION FOR THE ANHARMONIC OSCILLATOR." Modern Physics Letters A 06, no. 26 (August 30, 1991): 2429–35. http://dx.doi.org/10.1142/s0217732391002852.

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The recently derived Variational Random Phase Approximation is examined using the anharmonoic oscillator model. Special attention is paid to the ground state RPA wave function and the convergence of the proposed truncation scheme to obtain the diagonal density matrix.

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4

Terasaki, J., A. Smetana, F. Šimkovic, and M. I. Krivoruchenko. "Reproduction of exact solutions of Lipkin model by nonlinear higher random-phase approximation." International Journal of Modern Physics E 26, no. 10 (October 2017): 1750062. http://dx.doi.org/10.1142/s0218301317500628.

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It is shown that the random-phase approximation (RPA) method with its nonlinear higher generalization, which was previously considered as approximation except for a very limited case, reproduces the exact solutions of the Lipkin model. The nonlinear higher RPA is based on an equation nonlinear on eigenvectors and includes many particle-many hole components in the creation operator of the excited states. We demonstrate the exact character of solutions analytically for the particle number [Formula: see text] and, numerically, for [Formula: see text]. This finding indicates that the nonlinear higher RPA is equivalent to the exact Schrödinger equation, which opens up new possibilities for realistic calculations in many-body problems.

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5

Zhang, Min-Ye, Zhi-Hao Cui, and Hong Jiang. "Relative stability of FeS2polymorphs with the random phase approximation approach." Journal of Materials Chemistry A 6, no. 15 (2018): 6606–16. http://dx.doi.org/10.1039/c8ta00759d.

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6

JOHNSON, CALVIN W., and IONEL STETCU. "SHORTCUTS TO NUCLEAR STRUCTURE: LESSONS IN HARTREE–FOCK, RPA, AND THE NO-CORE SHELL MODEL." International Journal of Modern Physics E 14, no. 01 (February 2005): 57–65. http://dx.doi.org/10.1142/s0218301305002771.

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While the no-core shell model is a state-of-the-art microscopic approach to low-energy nuclear structure, its intense computational requirements lead us to consider time-honored approximations such as the Hartree–Fock (HF) approximation and the random phase approximation (RPA). We review RPA and point out some common misunderstandings, then apply HF + RPA to the no-core shell model. Here the main issue is appropriate treatment of contamination by spurious center-of-mass motion.

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7

Taqi, Ali H., R. A. Radhi, and Adil M. Hussein. "Low excitations of 16O using generalized density matrix random phase approximation GDRPA." International Journal of Modern Physics E 23, no. 08 (August 2014): 1450038. http://dx.doi.org/10.1142/s0218301314500384.

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The random phase approximation (RPA) equations based on the generalized density matrix (GDM), the so-called GDRPA are reformulated in a more compact matrix form, which renders the method especially suitable for realistic nuclear structure calculations. The GDRPA Hamiltonian is expressed in terms of the one-body particle–particle (pp) and hole–hole (hh) density matrices, and the nuclear force contributes not only in the particle–hole (ph) channel, as in normal ph-RPA, but also in the pp and hh channels. The Hamiltonian is diagonalized iteratively starting from initial guess values and the iterating process is carried out until self-consistency is achieved. The calculation in the model space 1p, 1d and 2s using Warburton and Brown interaction WBP is performed for 16 O . The GDRPA in the ph shell model calculations is tested, by comparing the energy eigenvalues and the electron scattering form factors with the results of the normal RPA and with the available experimental data.

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8

Fan, J. D., and Y. M. Malozovsky. "Electron correlation effects beyond the random phase approximation." International Journal of Modern Physics B 30, no. 13 (May 19, 2016): 1642006. http://dx.doi.org/10.1142/s0217979216420066.

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The methods that have been used to deal with a many-particle system can be basically sorted into three types: Hamiltonian, field theory and phenomenological method. The first two methods are more popular. Traditionally, the Hamiltonian method has been widely adopted in the conventional electronic theory for metals, alloys and semiconductors. Basically, the mean-field approximation (MFA) that has been working well for a weakly coupled system like a metal is employed to simplify a Hamiltonian corresponding to a particular electron system. However, for a strongly coupled many-particle system like a cuprate superconductor MFA should in principle not apply. Therefore, the field theory on the basis of Green’s function and the Feynman diagrams must be invoked. In this method, one is however more familiar with the random phase approximation (RPA) that gives rise to the same results as MFA because of being short of the information for higher-order terms of interaction. For a strongly coupled electron system, it is obvious that one has to deal with higher-order terms of a pair interaction to get a correct solution. Any ignorance of the higher-order terms implies that the more sophisticated information contained in those terms is discarded. However, to date one has not reached a consensus on how to deal with the higher-order terms beyond RPA. We preset here a method that is termed the diagrammatic iteration approach (DIA) and able to derive higher-order terms of the interaction from the information of lower-order ones on the basis of Feynman diagram, with which one is able to go beyond RPA step by step. It is in principle possible that all of higher-order terms can be obtained, and then sorted to groups of diagrams. It turns out that each of the groups can be replaced by an equivalent one, forming a diagrammatic Dyson-equation-like relation. The diagrammatic solution is eventually “translated” to a four-dimensional integral equation. The method can be applied to a layered 2D system that is a model system of cuprate superconductors and others such as atomic, nuclear, heavy-fermion systems, etc.

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9

MARIANO, A. "THE NUMBER SELF-CONSISTENT RENORMALIZED RANDOM PHASE APPROXIMATION." International Journal of Modern Physics B 20, no. 30n31 (December 20, 2006): 5334–37. http://dx.doi.org/10.1142/s0217979206036442.

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RPA and its quasiparticle generalization (QRPA) have been widely used to study electromagnetic transitions and beta decays in medium and heavy nuclei, being the pn-QRPA charge exchange mode extensively employed in the description of single and double beta decays in vibrational nuclei. However develops a collapse, i.e. it presents imaginary eigen-values for strengths beyond a critical value of the force. Extensions called renormalized QRPA (RQRPA) do not develop any collapse going beyond the simplest quasiboson approximation, however they present several drawbacks which will be analyzed.

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10

AVDEENKOV, A. V., D. S. KOSOV, and A. I. VDOVIN. "RENORMALIZED RPA AT FINITE TEMPERATURE." Modern Physics Letters A 11, no. 10 (March 28, 1996): 853–59. http://dx.doi.org/10.1142/s0217732396000850.

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A method taking account of a deviation of state occupation numbers from the thermal RPA prescriptions is elaborated to study collective excitations in hot nuclei. This thermal renormalized random phase approximation (TRRPA) is from Ken-Ji Hara and D.J. Rowe. In developing the TRRPA, a formalism of the thermofield dynamics (TFD) is used. Some numerical results are given for the SU(2) model.

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11

Tancic, Aleksandar, and M. R. Nikolic. "Optical potential approach to the slow positron scattering from helium atom." Facta universitatis - series: Physics, Chemistry and Technology 2, no. 4 (2002): 183–88. http://dx.doi.org/10.2298/fupct0204183t.

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We have extended our previous calculations to include the contribution of the random-phase approximation (RPA) (improved) optical potential to the low energy elastic scattering in the electron+He system. Our improved RPA calculations are shown to be in better agreement with the experimental values than other theoretical results.

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Grimme, Stefan, and Marc Steinmetz. "A computationally efficient double hybrid density functional based on the random phase approximation." Physical Chemistry Chemical Physics 18, no. 31 (2016): 20926–37. http://dx.doi.org/10.1039/c5cp06600j.

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13

PERDEW, JOHN P., and G. ROSENSTEEL. "METAL-SURFACE CORRELATION ENERGY FROM THE LIQUID DROP MODEL: A BACK-OF-THE-ENVELOPE ESTIMATE." Modern Physics Letters B 05, no. 16 (July 10, 1991): 1081–85. http://dx.doi.org/10.1142/s0217984991001325.

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The liquid drop model applied to the one-electron problem provides an elementary estimate of the correlation contribution to the surface and curvature energies of jellium, in terms of bulk electron density and bulk correlation energy. Within the random phase approximation (RPA), this estimate correctly predicts the size of the surface correlation energy, its strong dependence upon bulk density, and its weak dependence upon surface density profile. The local density approximation (LDA) to RPA predicts surface correlation energies that are far too small, as a consequence of the LDA self-interaction error. Possible implications beyond RPA are discussed. The power and limitations of the liquid drop expansion are illustrated by the example of one-electron jellium spheroids.

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14

Morawetz, K. "Stopping power in nonideal plasmas." Laser and Particle Beams 14, no. 4 (December 1996): 611–24. http://dx.doi.org/10.1017/s0263034600010338.

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The stopping power of dense nonideal plasmas is calculated in different many-body approximations. The T-matrix approximation of binary collisions is compared with the random phase approximation (RPA) approximation of dielectric fluctuations. It is found that RPA contributions are more important for dense plasmas at low temperatures. Within a microscopic model, the dynamical evolution of the velocity of the projectile is calculated. It reproduces experimental values well for the stopping of fast heavy ions at times after a pinch discharge. Further improvements due to memory effects and relaxation fields are discussed. A renormalization of the effective energy transfer by memory effects is presented.

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15

HOSOTANI, YUTAKA. "NEUTRAL AND CHARGED ANYON FLUIDS." International Journal of Modern Physics B 07, no. 12 (May 30, 1993): 2219–323. http://dx.doi.org/10.1142/s0217979293002857.

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Properties of neutral and charged anyon fluids are examined, with the main focus on the question of whether or not a charged anyon fluid exhibits a superconductivity at zero and finite temperature. Quantum mechanics of anyon fluids is precisely described by Chern-Simons gauge theory. The random phase approximation (RPA), the linearized self-consistent field method (SCF), and the hydrodynamic approach employed in the early analysis of anyon fluids are all equivalent. Relations and differences between neutral and charged anyon fluids are discussed. It is necessary to go beyond RPA and the linearized SCF, and possively beyond the Hartree-Fock approximation, to correctly describe various phenomena such as the flux quantization, vortex formation, and phase transition.

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16

Linh, Dang Khanh, and Nguyen Quoc Khanh. "Transport properties of bilayer graphene due to charged impurity scattering: Temperature-dependent screening and substrate effects." International Journal of Modern Physics B 32, no. 06 (February 26, 2018): 1850064. http://dx.doi.org/10.1142/s0217979218500649.

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We calculate the zero-temperature conductivity of bilayer graphene (BLG) impacted by Coulomb impurity scattering using four different screening models: unscreened, Thomas–Fermi (TF), overscreened and random phase approximation (RPA). We also calculate the conductivity and thermal conductance of BLG using TF, zero- and finite-temperature RPA screening functions. We find large differences between the results of the models and show that TF and finite-temperature RPA give similar results for diffusion thermopower S[Formula: see text]. Using the finite-temperature RPA, we calculate temperature and density dependence of S[Formula: see text] in BLG on SiO2, HfO2 substrates and suspended BLG for different values of interlayer distance c and distance between the first layer and the substrate d.

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17

Teruya, N., H. Dias, and A. F. R. de Toledo Piza. "Simple approximation to continuum random phase approximation (RPA): Application to the giant dipole resonance in 16O." Nuclear Physics A 556, no. 2 (May 1993): 157–64. http://dx.doi.org/10.1016/0375-9474(93)90345-x.

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18

ZETTILI, NOUREDINE. "ZERO-POINT FLUCTUATIONS IN THE NUCLEAR BORN-OPPENHEIMER GROUND STATE." Modern Physics Letters A 06, no. 03 (January 30, 1991): 183–88. http://dx.doi.org/10.1142/s0217732391000142.

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The small-amplitude oscillations of rigid nuclei around the equilibrium state are described by means of the nuclear Born-Oppenheimer (NBO) method. In this limit, the method is shown to give back the random phase approximation (RPA) equations of motion. The contribution of the zero-point fluctuations to the ground state are examined, and the NBO ground state energy derived is shown to be identical to the RPA ground state energy.

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19

Papakonstantinou, P., R. Roth, and N. Paar. "Nuclear response using correlated realistic interactions: first-order random phase approximation and beyond." HNPS Proceedings 15 (January 1, 2020): 67. http://dx.doi.org/10.12681/hnps.2621.

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A correlated realistic interaction derived within the Unitary Correlation Operator Method (UCOM) based on the Argonne V18 nucleon-nucleon potential is used in calculations of nuclear response for closed-shell nuclei. Giant resonances are examined in the framework of the random-phase approximation (RPA). The effects of explicit ground-state correla- tions and of higher than first-order configurations are discussed.

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20

Khanna, K. N., and G. Shanker. "The Structure Factor of Expanded Liquid Alkali Metals at the Long-Wavelength Limit." Zeitschrift für Naturforschung A 41, no. 6 (June 1, 1986): 823–25. http://dx.doi.org/10.1515/zna-1986-0609.

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S (0 ) values of expanded alkali metals are calculated in random phase approximation. The results reproduce positive values of S (0) at sufficiently high temperatures showing the validity of RPA in one-component plasma systems.

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21

PAAR, N., P. PAPAKONSTANTINOU, R. ROTH, and H. HERGERT. "SELF-CONSISTENT DESCRIPTION OF COLLECTIVE EXCITATIONS IN THE UNITARY CORRELATION OPERATOR METHOD." International Journal of Modern Physics E 15, no. 02 (March 2006): 346–53. http://dx.doi.org/10.1142/s0218301306004193.

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The fully self-consistent Random Phase Approximation (RPA) is constructed within the Unitary Correlation Operator Method (UCOM), which describes the dominant interaction-induced short-range central and tensor correlations by a unitary transformation. Based on the correlated Argonne V18 interaction, the RPA is employed in studies of multipole response in closed-shell nuclei across the nuclide chart. The UCOM-RPA results in a collective character of giant resonances, and it describes rather well the properties of isoscalar giant monopole resonances. However, the excitation energies of isovector giant dipole resonances and isoscalar giant quadrupole resonances are overestimated due to the missing long-range correlations and three-body contributions.

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22

TANATAR, B., and V. MOLDOVEANU. "RPA APPROACH TO NON-LINEAR TRANSPORT IN QUANTUM DOTS." International Journal of Modern Physics B 23, no. 20n21 (August 20, 2009): 4414–21. http://dx.doi.org/10.1142/s0217979209063560.

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An accurate theoretical treatment of electron-electron interactions in mesoscopic systems is available in very few cases and approximation schemes are developed in most of the applications, especially for many-level quantum dots. Here we present transport calculations within the random-phase approximation for the Coulomb interaction using the Keldysh Green's functions formalism. We describe the quantum dot systems by a tight-binding Hamiltonian. Our method is similar to the one used by Faleev and Stockman [Phys. Rev. B 66 085318 (2002)] in their study of the equilibrium properties of a homogeneous 2D electron gas. The important extension at the formal level is that we combine the RPA and the Keldysh formalism for studying non-linear transport properties of open quantum dots. Within the Keldysh formalism the polarization operator becomes a contour-ordered quantity that should be computed either from the non-interacting Green functions of the coupled quantum dot (the so-called G0W approximation) either self-consistently (GW approximation). We performed both non-selfconsistent and self-consistent calculations and compare the results. In particular we recover the Coulomb diamonds for interacting quantum dots and we discuss the charge sensing effects in parallel quantum dots.

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23

Su, He, Qiyang Wu, Hongyan Wang, and Hui Wang. "An assessment of the random-phase approximation functional and characteristics analysis for noncovalent cation–π interactions." Physical Chemistry Chemical Physics 19, no. 38 (2017): 26014–21. http://dx.doi.org/10.1039/c7cp04504b.

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The structure, binding energy, AIM, and RDG properties of noncovalent cation–π interactions are investigated systematically. We demonstrate that the random-phase approximation (RPA) functional can give an inexpensive description of noncovalent interactions in molecular clusters without sacrificing the accuracy compared to the high-level CCSD(T) method.

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24

Danielsen, Scott P. O., James McCarty, Joan-Emma Shea, Kris T. Delaney, and Glenn H. Fredrickson. "Molecular design of self-coacervation phenomena in block polyampholytes." Proceedings of the National Academy of Sciences 116, no. 17 (April 4, 2019): 8224–32. http://dx.doi.org/10.1073/pnas.1900435116.

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Coacervation is a common phenomenon in natural polymers and has been applied to synthetic materials systems for coatings, adhesives, and encapsulants. Single-component coacervates are formed when block polyampholytes exhibit self-coacervation, phase separating into a dense liquid coacervate phase rich in the polyampholyte coexisting with a dilute supernatant phase, a process implicated in the liquid–liquid phase separation of intrinsically disordered proteins. Using fully fluctuating field-theoretic simulations using complex Langevin sampling and complementary molecular-dynamics simulations, we develop molecular design principles to connect the sequenced charge pattern of a polyampholyte with its self-coacervation behavior in solution. In particular, the lengthscale of charged blocks and number of connections between oppositely charged blocks are shown to have a dramatic effect on the tendency to phase separate and on the accessible chain conformations. The field and particle-based simulation results are compared with analytical predictions from the random phase approximation (RPA) and postulated scaling relationships. The qualitative trends are mostly captured by the RPA, but the approximation fails catastrophically at low concentration.

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GOPAKUMAR, GEETHA, CHIRANJIB SUR, BHANU PRATAP DAS, RAJAT K. CHAUDHURI, DEBASHIS MUKHERJEE, and KIMIHIKO HIRAO. "RANDOM PHASE APPROXIMATION FOR ALLOWED AND PARITY NON-CONSERVING ELECTRIC DIPOLE TRANSITION AMPLITUDES AND ITS CONNECTION WITH MANY-BODY PERTURBATION THEORY AND COUPLED-CLUSTER THEORY." Journal of Theoretical and Computational Chemistry 05, no. 04 (December 2006): 945–56. http://dx.doi.org/10.1142/s0219633606002611.

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The connections between the Random Phase Approximation (RPA) and Many-Body Perturbation Theory (MBPT) and its all order generalization, the Coupled-Cluster Theory (CCT), have been explored. Explicit expressions have been derived for the electric dipole amplitudes for allowed and forbidden transitions induced by the parity non-conserving neutral weak interaction. The Goldstone diagrams associated with the RPA terms in both cases are shown to arise in MBPT and CCT, and the numerical verification of this relationship is made for the allowed electric dipole transitions.

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Rumyantsev, Artem M., and Igor I. Potemkin. "Explicit description of complexation between oppositely charged polyelectrolytes as an advantage of the random phase approximation over the scaling approach." Phys. Chem. Chem. Phys. 19, no. 40 (2017): 27580–92. http://dx.doi.org/10.1039/c7cp05300b.

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Formation of single globules via 1 : 1 complexation of oppositely charged linear chains occurs prior to coacervation. F_corr is proved to be negative which is the difference between the random phase approximation (RPA) correction term and the self-energy of the chains.

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27

Moinester, Murray A. "Multipole decomposition of Gamow–Teller strength." Canadian Journal of Physics 65, no. 6 (June 1, 1987): 660–65. http://dx.doi.org/10.1139/p87-094.

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Doubly differential continuum cross sections from the 90Zr(p, n)90Nb reaction have been analyzed via a multipoledecomposition technique. No quasi-free charge-exchange background has been subtracted, following the assumption that the observed cross sections are primarily due to one-step charge-exchange leading to 1p–1h states of all multipolarities to all excitations. The theoretical shapes of the differential cross sections for each Jπ multipole have been taken from random-phase approximation (RPA)–distorted-wave impulse approximation (DWIA) calculations. The experimental dσ/dΩ, for each 1 MeV excitation-energy bin have been decomposed into different multipole components by a least squares fit. This RPA-based analysis should determine the Jπ = 1+ cross sections with different, and also fewer, assumptions than usual for describing the underlying background. It can be of general importance in determining the extent of possible quenching of Gamow–Teller (GT) strength. The present decomposition accounts for all the theoretically predicted GT strength. The purpose of the present report is to illustrate an analysis based on RPA–DWIA shapes rather than to present final-decomposition results.

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Esmailian, A. H., F. Kanjouri, N. Mohammadi, M. R. Mahloojian, and N. Abbasi. "Spin-Waves in Stoner Ferromagnetic Phase of a Two-Dimensional Electron System." Solid State Phenomena 190 (June 2012): 15–18. http://dx.doi.org/10.4028/www.scientific.net/ssp.190.15.

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We have studied the collective excitations (spin-wave energies) in the ground state of a two-dimensional (2D) electron system using the random phase approximation (RPA). To do so, we have calculated the magnetic transverse susceptibility in 2D electron system by Hartree-Fock (HF) approximation of Hubbard model at T=0 which is generally referred to as the Stoner model. The spin-waves dispersion of three-dimensional (3D) electron system due to its quadratic behavior starts from zero at q0 while our numerical results show that the spin-waves dispersion of 2D electron system starts from the value Δ, known as exchange splitting energy, even at q=0.

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Rutonjski, Milica S., Milan R. Pantić, Slobodan M. Radošević, and Milica V. Pavkov-Hrvojević. "Magnetic Susceptibility of Quasi-two-dimensional Cuprate Antiferromagnets." Journal of Research in Physics 37, no. 1 (January 1, 2013): 19–32. http://dx.doi.org/10.2478/jrp-2013-0002.

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Abstract Parallel magnetic susceptibility temperature dependence of the high-TC superconducting parent compound La2CuO4 is calculated in both antiferromagnetic (AFM) and paramagnetic phase. By making use of the quantum Heisenberg three-dimensional AFM model including the in-plane spin anisotropy, the calculation is performed within the framework of three different theories: Green’s function theory in random-phase approximation (RPA), linear spinwave (LSW) theory and mean-field (MF) theory. The results suggest that at low temperatures quantum spin fluctuations play an important role, while at the temperatures above the critical one short-range correlations have a great impact on the behavior of the system. This leads to the discrepancy between RPA and MF results, since the later neglects the above phenomena. Further, LSW theory expectedly agrees with RPA results only at low temperatures where the magnon interactions are negligible. Comparison to the theoretical and experimental results quoted in literature confirms that RPA method presents the most appropriate method among the applied ones, suggesting that this approach is satisfactory in the case of the parallel magnetic susceptibility, while in order to reproduce the transversal one, spin-orbit coupling must be included.

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ESMAILIAN, A., and M. R. ABOLHASSANI. "QUASIPARTICLE LIFETIME OF A TWO-DIMENSIONAL ELECTRON GAS." International Journal of Modern Physics B 24, no. 09 (April 10, 2010): 1103–10. http://dx.doi.org/10.1142/s0217979210054014.

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We calculate the inelastic scattering lifetime of an excited quasiparticle at low (or zero) temperature, due to electron-electron interaction for a clean two-dimensional (2D) electron gas within the random-phase approximation (RPA) and compare it with the lifetime measured from the tunnelling experiment. Our result obtained by direct numerical calculation increases the electron relaxation rate considerably, hence decreases the size of discrepancy (roughly by a factor of 4) between theory and experiment which exists in the literature. We also show that including local-field factors in the effective electron interaction yields small correction to the result calculated within the RPA for rs ~ 1, corresponding to electron density of the sample in the tunnelling experiment. This result suggests that the RPA is reasonably accurate for a 2D electron gas in weak coupling limit.

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Barriga-Carrasco, Manuel D. "Applying full conserving dielectric function to the energy loss straggling." Laser and Particle Beams 29, no. 1 (February 10, 2011): 81–86. http://dx.doi.org/10.1017/s0263034610000789.

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AbstractThe purpose of this paper is to calculate proton energy loss straggling using a full conserving dielectric function (FCDF) for plasmas at any degeneracy. This dielectric function takes into account plasma electron-electron collision considering density, momentum, and energy conservation. When only momentum conservation law is accomplished, the FCDF reproduces the well known Mermin dielectric function, when none of the conservations laws are obeyed, the random phase approximation (RPA) is recovered. Then, the FCDF is applied for the first time to the determination of the energy loss straggling. Differences among diverse dielectric functions to determine straggling follow the same behavior for all kind of plasmas then, they do not depend on the plasma degeneracy but essentially do on the value of the collision frequency. These discrepancies can rise up to 5% between FCDF values and the Mermin ones, and 2% between the FCDF ones and RPA ones for plasma with high enough collision frequency. The similarity between FCDF and RPA results is not surprising, as all conservation laws are also considered in RPA dielectric function. The fact that FCDF and RPA give similar results and the fact that FCDF considers electron-electron collisions and RPA does not, means that latter collisions are not significant for energy loss straggling calculations.

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Sakamoto, Hideo. "Some Properties of Coupled RPA Equations with Separable Interactions." International Journal of Modern Physics E 06, no. 02 (June 1997): 251–58. http://dx.doi.org/10.1142/s0218301397000159.

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We investigate some properties of coupled eigenvalue equations in the random phase approximation for fundamental modes of motion in a nuclear many-body system undergoing several separable two-body interactions. Based on the Sturm's method, a new algorithm is proposed for solving such coupled secular equations and for testing the stability condition of the Hartree-Fock ground state. A transition strength in general is expressed in a compact form and, in a restricted case, a continuous strength function is constructed by averaging with a Lorentzian distribution function.

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33

Barriga-Carrasco, M. D. "Mermin dielectric function versus local field corrections on proton stopping in degenerate plasmas." Laser and Particle Beams 26, no. 3 (July 7, 2008): 389–95. http://dx.doi.org/10.1017/s0263034608000402.

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AbstractIf plasmas are considered fully ionized, the electronic stopping of a charged particle that traverses them will only be due to free electrons. This stopping can be obtained in a first view through the random phase approximation (RPA). But free electrons interact between them affecting the stopping. These interactions can be taken into account in the dielectric formalism by means of two different ways: the Mermin function or the local field corrections (LFCs). LFCs produce an enhancement in stopping before the maximum and recover the RPA values just after it. Mermin method also produces firstly a high increase at very low energies, then a small enhancement at low energies and finally decreases below RPA values before and after the maximum. Differences between the two methods are very important at very low energies and by 30% around the stopping maximum.

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34

Wambach, J. "Recent theoretical developments in nuclear charge-exchange reactions." Canadian Journal of Physics 65, no. 6 (June 1, 1987): 614–25. http://dx.doi.org/10.1139/p87-087.

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The (p, n) and (n, p) charge-exchange reactions are a suitable tool in nuclear-structure studies. At intermediate energies, the interaction with the target resembles that between free nucleons, which makes the probes mostly susceptible to the spin dynamics of the nucleus. We review the current theoretical picture of nucleon–nucleus charge-exchange reactions. A brief introduction to the theory of direct reactions in the impulse approximation is given. We then discuss the random-phase approximation (RPA) linear response theory, which is widely used in the calculation of cross sections and related observables. To understand correctly the shape of the continuum cross sections, one needs a more sophisticated theory. We discuss suitable extensions of the RPA that incorporate spreading effects as well as escape effects. Charge-exchange reactions of the (n, p) type have important implications for the evolution of massive stars. The relevance for Type-II supernovae is discussed.

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35

KVASIL, J., A. REPKO, V. O. NESTERENKO, W. KLEINIG, and P. G. REINHARD. "E1 STRENGTH IN LIGHT NUCLEI: SKYRME RPA ANALYSIS." International Journal of Modern Physics E 21, no. 05 (May 2012): 1250041. http://dx.doi.org/10.1142/s0218301312500413.

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The giant dipole resonance (GDR) in N = 28 isotones (48 Ca , 50 Ti , 52 Cr , 54 Fe ) is analyzed in the framework of the Skyrme random-phase-approximation (RPA). Three Skyrme forces, SkM*, SLy6 and SV-bas, are used. The effects beyond RPA are simulated by the double folding procedure. We show that dipole strength exhibits a large collective shift, which testifies to a strong impact of the residual interaction and signals on considerable anharmonic effects. In 52 Cr , a significant pairing impact is found. For exception of 50 Ti , an acceptable agreement with the experiment data is obtained, which justifies the ability of Skyrme forces to describe GDR in light nuclei.

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36

Amor-Quiroz, D. A., T. Yépez-Martínez, P. O. Hess, O. Civitarese, and A. Weber. "Low-energy meson spectrum from a QCD approach based on many-body methods." International Journal of Modern Physics E 26, no. 12 (December 2017): 1750082. http://dx.doi.org/10.1142/s0218301317500823.

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The Tamm–Dancoff Approximation (TDA) and Random Phase Approximation (RPA) many-body methods are applied to an effective Quantum Chromodynamics (QCD) Hamiltonian in the Coulomb gauge. The gluon effects in the low-energy domain are accounted for by the Instantaneous color-Coulomb Interaction between color-charge densities, approximated by the sum of a Coulomb ([Formula: see text]) and a confining linear ([Formula: see text]) potential. We use the eigenfunctions of the harmonic oscillator as a basis for the quantization of the quark fields, and discuss how suitable this basis is in various steps of the calculation. We show that the TDA results already reproduce the gross-structure of the light-flavored meson states. The pion-like state, which in the RPA description is a highly collective state, is in better agreement with the experimental value. The results are related to other nonperturbative treatments and compared to experimental data. We discuss the advantages of the present approach.

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37

RABHI, AZIZ, MARTA BRAJCZEWSKA, PETER SCHUCK, JOÃO DA PROVIDÊNCIA, and RAOUF BENNACEUR. "THE 1D HEISENBERG ANTIFERROMAGNET MODEL BY THE VARIATION AFTER PROJECTION METHOD." International Journal of Modern Physics B 27, no. 14 (May 19, 2013): 1350058. http://dx.doi.org/10.1142/s0217979213500586.

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The four site and eight site 1D anti-ferromagnetic Heisenberg chains in the Jordan–Wigner representation are investigated within the standard Hartree–Fock and random phase approximation (RPA) approaches, both in the symmetry unbroken and in the symmetry broken phases. A translation invariant groundstate, obtained by the projection method as a linear combination of a symmetry-broken HF state and its image under reflection, is also considered, for each chain type. It is found that the projection method considerably improves the HF treatment for instance as far as the groundstate energy is concerned, but also with respect to the RPA energies. The results are furthermore confronted with the ones obtained within so-called SCRPA scheme.

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38

Morawetz, K. "Stopping Power in Strongly Coupled Plasmas." Laser and Particle Beams 15, no. 4 (December 1997): 507–21. http://dx.doi.org/10.1017/s0263034600011095.

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The stopping power of dense nonideal plasmas is calculated in different approximations. The T-matrix approximation for binary collisions is compared with the random phase approximation (RPA) approximation for dielectric fluctuations. Within a microscopic model, the dynamical evolution of the velocity of the projectile is calculated. It reproduces well experimental values for the stopping of fast heavy ions. Further improvements due to correlations are discussed. Both concepts, cluster decomposition and memory, are compared and it is found that they lead to the same quantum virial corrections of the Beth-Uhlenbeck type in equilibrium. However, memory in the kinetic equation causes an additional renormalization of the effective energy transfer in nonequilibrium.

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39

Zhang, C. "Electromagnetic Absorption in Two-dimensional Systems under a Magnetic Field and a Unidirectional Periodic Potential." Australian Journal of Physics 53, no. 1 (2000): 65. http://dx.doi.org/10.1071/ph99024.

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The absorption of electromagnetic waves by a high mobility two-dimensional electron gas subjected to a magnetic field and a weak periodic potential is investigated. We show that the periodic modulation on the Laudau states has a profound effect on the absorption of electromagnetic waves. We develop a formalism which treats the electron–electron interaction beyond the random-phase-approximation (RPA) and includes the electron-impurity scattering in the lowest order. A RPA dielectric function was employed to study the electromagnetic absorption in modulated systems. Simultaneous excitation of an electron–hole pair with finite momentum contributes significantly to the absorption around and below the cyclotron frequency. Such a process is absent for a uniform electron gas under a magnetic field.

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40

RADUTA, A. A., and R. BUDACA. "SUM RULE FOR A SCHIFF-LIKE DIPOLE MOMENT." International Journal of Modern Physics B 25, no. 04 (February 10, 2011): 467–78. http://dx.doi.org/10.1142/s0217979211057918.

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The energy-weighted sum rule for an electric dipole transition operator of a Schiff type differs from the Thomas–Reiche–Kuhn (TRK) sum rule by several corrective terms which depend on the number of system components, [Formula: see text]. For illustration the formalism was applied to the case of Na clusters. One concludes that the random phase approximation (RPA) results for Na clusters obey the modified TRK sum rule.

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KVASIL, J., V. O. NESTERENKO, W. KLEINIG, D. BOŽÍK, and P. G. REINHARD. "SKYRME–HARTREE–FOCK DESCRIPTION OF THE DIPOLE STRENGTH IN NEUTRON-RICH TIN ISOTOPES." International Journal of Modern Physics E 20, no. 02 (February 2011): 281–91. http://dx.doi.org/10.1142/s0218301311017636.

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Low-energy E1 strength in neutron-rich 132-164 Sn isotopes is analyzed in the framework of the Skyrme random phase approximation (RPA) with different Skyrme forces. A double folding procedure is applied to take into account the energy-dependent width effects beyond RPA. All the considered Skyrme forces indicate a soft prolate deformation in the open shell isotopes 142-164 Sn . The integrated E1 strength in the energy region of the pygmy resonance grows with the neutron number. The influence of deformation on the integrated strength near the particle emission thresholds (which is of a keen astrophysical interest) is strictly suppressed by the mutual compensation effect for the branches of the giant dipole resonance. The results obtained are in a good agreement with the previous findings of the relativistic mean field model.

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42

Jørgensen, Maria W., and Stephan P. A. Sauer. "Benchmarking doubles-corrected random-phase approximation methods for frequency dependent polarizabilities: Aromatic molecules calculated at the RPA, HRPA, RPA(D), HRPA(D), and SOPPA levels." Journal of Chemical Physics 152, no. 23 (June 21, 2020): 234101. http://dx.doi.org/10.1063/5.0011195.

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43

Kardaras, I. S., V. N. Stavrou, I. G. Tsoulos, and T. S. Kosmas. "Detailed calculations for muon capture rates within the quasi-particle RPA." HNPS Proceedings 18 (November 23, 2019): 175. http://dx.doi.org/10.12681/hnps.2549.

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Detailed calculations for bound muon capture in complex nuclei are performed by employing the quasi particle random phase approximation (QRPA). The required bound muon wavefunctions for the large and the small components of the Dirac muon wavefunctions are obtained by using the genetic algorithm approach. We ob- tained contributions for 2p muon orbit; that is to say wavefunctions for atomic ex- cited state of the muonic atoms in nucleus 28Si. As a byproduct the above method give the corresponding energies to these wavefunctions which are compared with those of other methods. Our goal is to use the method developed recently by Laganke, Zinner and Vogel and our advantageous numerical approach to obtain state by state calculations of the muon capture rates within the QRPA.

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44

Nishiyama, Seiya, and João da Providência. "Modified non-Euclidean transformation on the SO(2N+2) U(N+1) Grassmannian and SO(2N + 1) random phase approximation for unified description of Bose and Fermi type collective excitations." International Journal of Geometric Methods in Modern Physics 13, no. 04 (March 31, 2016): 1650043. http://dx.doi.org/10.1142/s0219887816500432.

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In a slight different way from the previous one, we propose a modified non-Euclidean transformation on the [Formula: see text] Grassmannian which gives the projected [Formula: see text] Tamm–Dancoff equation. We derive a classical time-dependent (TD) [Formula: see text] Lagrangian which, through the Euler–Lagrange equation of motion for [Formula: see text] coset variables, brings another form of the previous extended-TD Hartree–Bogoliubov (HB) equation. The [Formula: see text] random phase approximation (RPA) is derived using Dyson representation for paired and unpaired operators. In the [Formula: see text] HB case, one boson and two boson excited states are realized. We, however, stress non-existence of a higher RPA vacuum. An integrable system is given by a geometrical concept of zero-curvature, i.e. integrability condition of connection on the corresponding Lie group. From the group theoretical viewpoint, we show the existence of a symplectic two-form [Formula: see text].

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Ren, Zhongzhu, A. Faessler, and T. S. Kosmas. "Study of the exotic μ-e conversion in nuclei using RQRPA." HNPS Proceedings 9 (February 11, 2020): 1. http://dx.doi.org/10.12681/hnps.2772.

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The neutrinoless muon-to-electron conversion in nuclei is studied by using the renormalized quasiparticle random-phase approximation (RQRPA). This generalization of RPA is more reliable for the extremely small (μ-,e-) transition matrix elements than the ordinary QRPA because it restores the Pauli principle to a large extent. We apply the method to a set of nuclei throughout the periodic table, but we specifically investigate the 48Ti and 208Pb nuclei which are currently used as stopping targets at the PSI μ-e conversion experiments with the SINDRUM II spectrometer.

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Wang, Yanzhao, Ligang Cao, Jianzhong Gu, and Zhaoyu Hou. "Tensor force effect on incompressibility of bubble nucleus." International Journal of Modern Physics E 23, no. 12 (December 2014): 1450082. http://dx.doi.org/10.1142/s0218301314500827.

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The tensor force effect on the isoscalar giant monopole resonance (ISGMR) of 46 Ar is investigated in the framework of Hartree–Fock (HF) + random phase approximation (RPA) approach with the Skyrme interactions SLy5, SLy5+T and SLy5+ T w. By using the ISGMR excitation energy, the incompressibility value of 46 Ar is extracted. It is shown that the incompressibility is enhanced with the SLy5+T interaction compared to the one with the SLy5 interaction. However, the SLy5+ T w interaction makes the incompressibility smaller because of the bubble structure of 46 Ar .

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47

Lošić, Željana Bonačić. "Coupling of plasmon and dipolar modes in a monolayer of MoS2." Modern Physics Letters B 28, no. 12 (May 19, 2014): 1450099. http://dx.doi.org/10.1142/s0217984914500997.

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The dielectric function of a monolayer of molybdenum disulfide is investigated within the model of two-band metal using the random phase approximation (RPA). The large direct bandgap in a monolayer of MoS 2 leads to the appearance of the interband dipolar mode which couples to the intraband plasmon mode. This results in two hybridized modes. The renormalized dipolar mode is close to its bare value, while coupling suppresses the plasmon mode. The obtained modes are responsible for the appearance of dispersing peaks in the energy-loss function.

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48

NAZMITDINOV, R. G., and A. PUENTE. "SYMMETRY BREAKING PHENOMENA IN MESOSCOPIC SYSTEMS: QUANTUM DOTS AND ROTATING NUCLEI." International Journal of Modern Physics E 18, no. 04 (April 2009): 1014–21. http://dx.doi.org/10.1142/s0218301309013178.

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A brief description of excited and ground states in two-dimensional quantum dots and rotating nuclei is presented within a mean field approach and a random-phase approximation (RPA). We discuss the procedure to restore the rotational symmetry broken at the mean field, which can be extended for other symmetry breaking cases. We propose to consider a disappearance of collective excitations in the rotating frame as a manifestation of symmetry breaking phenomena of the rotating mean field. In particular, we demonstrate that the disappearance of a collective octupole mode in the rotating frame in 162 Yb gives rise to the nonaxial octupole deformation.

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49

KOSOV, D. S., and A. I. VDOVIN. "THE TFD TREATMENT OF THE QUASIPARTICLE-PHONON INTERACTION AT FINITE TEMPERATURE." Modern Physics Letters A 09, no. 19 (June 21, 1994): 1735–43. http://dx.doi.org/10.1142/s0217732394001581.

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The coupling of elementary excitation modes in hot nuclei is studied. For this aim the quasiparticle-phonon nuclear model (QPM) is extended to a finite temperature by using the formalism of the thermofield dynamics. First the energies and structures of one-phonon states are calculated in the thermal random phase approximation and then the thermal QPM Hamiltonian HQPM is expressed in terms of thermal quasiparticles and thermal RPA-phonons. The equation for the energies taking into account mixing of one-and two-thermal phonon states is derived. The expression of the coupling matrix element between thermal phonons is given.

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50

BOZKURT, KUTSAL. "ISOVECTOR PYGMY DIPOLE EXCITATION IN NEUTRON-RICH NUCLEI." Modern Physics Letters A 25, no. 34 (November 10, 2010): 2905–13. http://dx.doi.org/10.1142/s021773231003389x.

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We investigate isovector pygmy dipole resonance (IVPDR) for the case of neutron-rich nuclei 68 Ni , 130 Sn and 134 Sn using effective nucleon–nucleon Skyrme interaction. We use the Hartree–Fock–Bogoliubov (HFB) theory and employ the (quasiparticle) random phase approximation (Q)RPA. We calculate and compare the PDR strength in the PDR energy region for the case of density dependent central and full interaction modes for RPA and QRPA calculations. We observe that the results for the pygmy dipole resonance for neutron-rich soft nuclei 68 Ni that we consider are in reasonable agreement with their experimental results in both interactions and calculations. We also study the PDR for highly neutron-rich heavy nuclei, such as 130 Sn and 134 Sn . We see that only the QRPA calculation with full interaction is in good agreement with the experimental results for these nuclei and with a recent study in the literature. We find that the PDR strength distribution sensitively depends on the chosen interaction modes, especially for the neutron-rich heavy nuclei 134 Sn .

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