Generalized dynamical random phase approximation for the collective Green's function of the anisotropic Heisenberg ferromagnet

1979 ◽  
Vol 40 (1) ◽  
pp. 633-640 ◽  
Author(s):  
Yu. G. Rudoi
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Random Phase Approximation ◽  
Random Phase ◽  
Heisenberg Ferromagnet ◽  
Phase Approximation

scholarly journals DENSITY-DEPENDENT PHONORITON STATES IN HIGHLY EXCITED SEMICONDUCTORS

1995 ◽  
Vol 09 (28) ◽  
pp. 3725-3733
Author(s):  
NGUYEN HONG QUANG ◽  
NGUYEN MINH KHUE
Keyword(s):  
Green's Function ◽  
Random Phase Approximation ◽  
Function Method ◽  
Random Phase ◽  
High Density ◽  
Phase Approximation ◽  
Green’S Function Method ◽  
Exciton Density ◽  
Density Dependent ◽  
Exciton Interaction

The dynamical aspects of the phonoriton state in highly-photoexcited semiconductors is studied theoretically. The effect of the exciton–exciton interaction and nonbosonic character of high-density excitons are taken into account. Using Green's function method and within the Random Phase Approximation it is shown that the phonoriton dispersion and damping are very sensitive to the exciton density, characterizing the excitation degree of semiconductors.

High-temperature susceptibility of a Heisenberg ferromagnet using Green function theory

1968 ◽  
Vol 46 (12) ◽  
pp. 1502-1504 ◽  
Author(s):  
S. T. Dembinski
Keyword(s):  
High Temperature ◽  
Green Function ◽  
Random Phase Approximation ◽  
Function Theory ◽  
Random Phase ◽  
Heisenberg Ferromagnet ◽  
Zero Field ◽  
Phase Approximation ◽  
First Order ◽  
Temperature Susceptibility

A new first-order decoupling recently proposed, which gave very satisfactory results for the low-temperature magnetization of a Heisenberg [Formula: see text] ferromagnet, is used here to calculate the high-temperature zero-field susceptibility series. The results are close to those known from the random-phase-approximation decoupling.

Interpretation of Preferential Adsorption Using Random Phase Approximation Theory

1995 ◽  
Vol 60 (10) ◽  
pp. 1641-1652 ◽  
Author(s):  
Henri C. Benoît ◽  
Claude Strazielle
Keyword(s):  
Approximation Theory ◽  
Random Phase Approximation ◽  
Virial Coefficient ◽  
Random Phase ◽  
Second Virial Coefficient ◽  
Solvent Mixture ◽  
Gyration Radius ◽  
Thermodynamic Quantities ◽  
Phase Approximation ◽  
Preferential Adsorption

It has been shown that in light scattering experiments with polymers replacement of a solvent by a solvent mixture causes problems due to preferential adsorption of one of the solvents. The present paper extends this theory to be applicable to any angle of observation and any concentration by using the random phase approximation theory proposed by de Gennes. The corresponding formulas provide expressions for molecular weight, gyration radius, and the second virial coefficient, which enables measurements of these quantities provided enough information on molecular and thermodynamic quantities is available.

Non-Equilibrium Green’s Functions: Variational Relations and Approximations for Particle Interactions

2018 ◽  
Author(s):  
Norman J. Morgenstern Horing
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Green's Functions ◽  
Green’S Functions ◽  
Random Phase ◽  
Integration Contour ◽  
Differential Formulation ◽  
Variational Relations ◽  
Potential Perturbation ◽  
Non Equilibrium

Chapter 09 Nonequilibrium Green’s functions (NEGF), including coupled-correlated (C) single- and multi-particle Green’s functions, are defined as averages weighted with the time-development operator U(t0+τ,t0). Linear conductivity is exhibited as a two-particle equilibrium Green’s function (Kubo-type formulation). Admitting particle sources (S:η,η+) and non-conservation of number, the non-equilibrium multi-particle Green’s functions are constructed with numbers of creation and annihilation operators that may differ, and they may be derived as variational derivatives with respect to sources η,η+ of a generating functional eW=TrU(t0+τ,t0)CS/TrU(t0+τ,t0)C. (In the non-interacting case this yields the n-particle Green’s function as a permanent/determinant of single-particle Green’s functions.) These variational relations yield a symmetric set of multi-particle Green’s function equations. Cumulants and the Linked Cluster Theorem are discussed and the Random Phase Approximation (RPA) is derived variationally. Schwinger’s variational differential formulation of perturbation theories for the Green’s function, self-energy, vertex operator, and also shielded potential perturbation theory, are reviewed. The Langreth Algebra arises from analytic continuation of integration of products of Green’s functions in imaginary time to the real-time axis with time-ordering along the integration contour in the complex time plane. An account of the Generalized Kadanoff-Baym Ansatz is presented.

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