Dielectric response of metallic crystal made up of highly polarisable molecules: the semi-classical approach

Open Physics ◽  
2009 ◽  
Vol 7 (4) ◽  
Author(s):  
Željana Bonačić Lošić ◽  
Paško Županović
Keyword(s):  
Dielectric Function ◽  
Dielectric Response ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Collective Modes ◽  
Classical Approach ◽  
Phase Approximation ◽  
Many Body ◽  
Band Insulator ◽  
The Many

AbstractThe dielectric response is considered within models of a one-band metal, a two-band insulator and a two-band metal using the semi-classical approximation. Corresponding dielectric functions are found. The dielectric function of two-band metal is found to be the interpolation between the Sellmeyer and Lorenz-Lorentz expressions, respectively. The frequencies of the collective modes are identified as the zeroes of the dielectric functions. The correspondence between the semi-classical approach used in this paper and the many-body calculation within the random-phase approximation is established.

scholarly journals Hartree–Fock and random phase approximation theories in a many-fermion solvable model

2015 ◽  
Vol 30 (36) ◽  
pp. 1550196 ◽  
Author(s):  
Giampaolo Co’ ◽  
Stefano De Leo
Keyword(s):  
Random Phase Approximation ◽  
Random Phase ◽  
Solvable Model ◽  
Phase Approximation ◽  
Many Body ◽  
Hartree Fock ◽  
Ideal System ◽  
The Many ◽  
Effective Theories ◽  
Number Of Particles

We present an ideal system of interacting fermions where the solutions of the many-body Schrödinger equation can be obtained without making approximations. These exact solutions are used to test the validity of two many-body effective approaches, the Hartree–Fock and the random phase approximation theories. The description of the ground state done by the effective theories improves with increasing number of particles.

scholarly journals Full conserving dielectric function for plasmas at any degeneracy

2010 ◽  
Vol 28 (2) ◽  
pp. 307-311 ◽  
Author(s):  
Manuel D. Barriga-Carrasco
Keyword(s):  
Conservation Laws ◽  
Dielectric Function ◽  
Dielectric Response ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Plasma Temperature ◽  
Phase Approximation ◽  
Approximation Model ◽  
Relevant Issue ◽  
Electron Collisions

AbstractDielectric functions of an electron plasma are calculated for an electron gas in which number, momentum, and energy are conserved during electron-electron collisions. They are compared with others in the literature, revealing that, in general, that imposition of the conservation laws tends to make the full conserving dielectric response more similar to the random phase approximation dielectric response than without it. This is due to the fact that in the random phase approximation model all the conservation laws are also enforced. Our model is checked for other plasma degeneracies; concretely we consider partially degenerate plasmas and classical plasmas. The behaviour of the dielectric functions of these plasmas is similar to the degenerate one. Differences among dielectric functions are more significant than for the degenerate case, but it is mainly due to low relaxation time values. The most relevant issue for these plasmas is the fact that the consideration of energy conservation in the dielectric function is more important in these cases, because plasma temperature is significant.

scholarly journals Estimation of nuclear matrix elements of double-$$\varvec{\beta }$$ decay from shell model and quasiparticle random-phase approximation

2021 ◽  
Vol 136 (9) ◽  
Author(s):  
J. Terasaki ◽  
Y. Iwata
Keyword(s):  
Shell Model ◽  
Nuclear Matrix ◽  
Single Particle ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Nuclear Matrix Element ◽  
Phase Approximation ◽  
Quasiparticle Random Phase Approximation ◽  
Calculation Results ◽  
The Many

AbstractThe nuclear matrix element (NME) of neutrinoless double-$$\beta $$ β ($$0\nu \beta \beta $$ 0 ν β β ) decay is an essential input for determining the neutrino effective mass, if the half-life of this decay is measured. Reliable calculation of this NME has been a long-standing problem because of the diversity of the predicted values of the NME, which depends on the calculation method. In this study, we focus on the shell model and the QRPA. The shell model has a rich amount of the many-particle many-hole correlations, and the quasiparticle random-phase approximation (QRPA) can obtain the convergence of the calculation results with respect to the extension of the single-particle space. It is difficult for the shell model to obtain the convergence of the $$0\nu \beta \beta $$ 0 ν β β NME with respect to the valence single-particle space. The many-body correlations of the QRPA may be insufficient, depending on the nuclei. We propose a new method to phenomenologically modify the results of the shell model and the QRPA compensating for the insufficiencies of each method using the information of other methods in a complementary manner. Extrapolations of the components of the $$0\nu \beta \beta $$ 0 ν β β NME of the shell model are made toward a very large valence single-particle space. We introduce a modification factor to the components of the $$0\nu \beta \beta $$ 0 ν β β NME of the QRPA. Our modification method yields similar values of the $$0\nu \beta \beta $$ 0 ν β β NME for the two methods with respect to $$^{48}$$ 48 Ca. The NME of the two-neutrino double-$$\beta $$ β decay is also modified in a similar but simpler manner, and the consistency of the two methods is improved.

scholarly journals Fundamental nuclear structure symmetries in double beta decay processes

2020 ◽  
Vol 9 ◽  
pp. 211
Author(s):  
O. Civitarese
Keyword(s):  
Nuclear Structure ◽  
Beta Decay ◽  
Random Phase Approximation ◽  
Body Problem ◽  
Random Phase ◽  
Double Beta Decay ◽  
Phase Approximation ◽  
Many Body ◽  
Quasiparticle Random Phase Approximation ◽  
Fundamental Symmetries

The nuclear structure physics of double beta decay transitions is reviewed starting from the consideration of fundamental symmetries of the nuclear many body problem. The problems found in the use of the Quasiparticle Random Phase Approximation (QRPA) and related approximations, in dealing with the calculation of nuclear double beta decay observables, are understood in terms of the mixing between isospin collective and intrinsic variables.

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