Analysis of Collective Resonances in Clusters: Metals and Carbon

1992 ◽  
Vol 272 ◽  
Author(s):  
Vitaly V. Kresin
Keyword(s):  
Random Phase Approximation ◽  
Sum Rules ◽  
Random Phase ◽  
Closed Shell ◽  
Dynamical Response ◽  
Many Body ◽  
Resonance Frequencies ◽  
Unified View ◽  
Small Clusters ◽  
Good Agreement

ABSTRACTDipole photoabsorption spectra of small clusters are analyzed. Two types of systems are considered: metal clusters and the carbon fullerenes. Both have been found to exhibit strong collective photoabsorption modes associated with the motion of delocalized electrons. We describe analytical results for the resonance frequencies in both spherical (closed-shell metallic, C60 ) and spheroidal (openshell metallic, C70) particles. The calculation is based on the techniques of many-body physics (random-phase approximation, sum rules), affords a unified view of the dynamical response of microscopic clusters, and leads to good agreement with experimental data.

Some Properties of Coupled RPA Equations with Separable Interactions

1997 ◽  
Vol 06 (02) ◽  
pp. 251-258 ◽  
Author(s):  
Hideo Sakamoto
Keyword(s):  
Ground State ◽  
Random Phase Approximation ◽  
Strength Function ◽  
Random Phase ◽  
Transition Strength ◽  
Body System ◽  
Many Body ◽  
Hartree Fock ◽  
Secular Equations ◽  
The Stability

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.

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.

scholarly journals Dynamic response of some atoms: Many-body calculations

2005 ◽  
Vol 3 (2) ◽  
pp. 129-140 ◽  
Author(s):  
Aleksandar Tancic ◽  
M. Nikolic
Keyword(s):  
Random Phase Approximation ◽  
Random Phase ◽  
Atomic Interaction ◽  
Correlation Effects ◽  
Many Body ◽  
Hartree Fock ◽  
Many Body Theory ◽  
Correlation Potential ◽  
Body Theory ◽  
True Correlation

The frequency-dependent polarizability in the Hartree-Fock (HF) approximation has been corrected for true correlation effects by means of many-body theory. The polarizability has been computed in the Random Phase Approximation with Exchange (RPAE) for He, Ar Xe, Kr, Li, Ca through the second (and some higher) order in the correlation potential. With this polarizability as input we obtained the values of some atomic interaction constants.

Many-Electron Correlations in the Photoionization of a Nitrogen Atom

1974 ◽  
Vol 52 (4) ◽  
pp. 349-354 ◽  
Author(s):  
N. A. Cherepkov ◽  
L. V. Chernysheva ◽  
V. Radojević ◽  
I. Pavlin
Keyword(s):  
Nitrogen Atom ◽  
Cross Section ◽  
Cross Sections ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Electron Correlations ◽  
Sum Rule ◽  
Hartree Fock ◽  
The Cross ◽  
Good Agreement

Photoionization cross sections for the outer shell of the nitrogen atom ground state are calculated in the single-particle Hartree–Fock approximation and, in order to take into account many-electron correlations, also in the Random Phase Approximation with Exchange (RPAE). To be able to apply the RPAE, its modification for the half-filled shell atom, such as nitrogen atom, is presented. Calculation of length and velocity forms of the cross section in both approximations are compared with the available experimental data, and a good agreement is obtained. It has been found that in the RPAE the influence of many-electron correlations in a nitrogen atom is not great, but it is very important since, in contrast to the Hartree–Fock approximation, it results in the validity of the sum rule and the coincidence of the length and velocity forms of the cross sections, in agreement with the requirement of the general theory. The angular distribution of photoelectrons is also calculated in the RPAE, which has not been measured so far.

scholarly journals Low-energy meson spectrum from a QCD approach based on many-body methods

2017 ◽  
Vol 26 (12) ◽  
pp. 1750082 ◽  
Author(s):  
D. A. Amor-Quiroz ◽  
T. Yépez-Martínez ◽  
P. O. Hess ◽  
O. Civitarese ◽  
A. Weber
Keyword(s):  
Random Phase Approximation ◽  
Random Phase ◽  
Low Energy ◽  
Collective State ◽  
Many Body ◽  
Color Charge ◽  
Charge Densities ◽  
Linear Formula ◽  
Energy Domain ◽  
Meson States

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.

scholarly journals Random Phase Approximation Applied to Many-Body Noncovalent Systems

2019 ◽  
Vol 16 (1) ◽  
pp. 427-442 ◽  
Author(s):  
Marcin Modrzejewski ◽  
Sirous Yourdkhani ◽  
Jiří Klimeš
Keyword(s):  
Random Phase Approximation ◽  
Random Phase ◽  
Phase Approximation ◽  
Many Body
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