Effective density functionals beyond mean field

Boson-fermion Model beyond Mean-field Approximation

A model of hybridized bosons and fermions is studied beyond the mean field approximation. The divergent boson self-energy at zero temperature makes the Cooper pairing of fermions impossible. The frequency and momentum dependence of the self-energy and the condensation temperature T c of initially localized bosons are calculated analytically. The value of the boson condensation temperature T c i...

Beyond Gross-Pitaevskii Mean Field Theory

Pairing Correlations beyond the Mean Field

Self-consistent mean-field models are one of the standard approaches in nuclear structure theory, see Ref.1 for a recent review. For heavy nuclei, they are the only microscopic method that can be systematically applied on a large scale. Over the last few years, we were involved in the development of a method, that adds long-range correlations to self-consistent mean-field by projection after va...

The Bose gas beyond mean field

We study a homogeneous Bose gas with purely repulsive forces. Using the Kac scaling of the binary potential we derive analytically the form of the thermodynamic functions of the gas for small but finite values of the scaling parameter in the low density regime. In this way we determine dominant corrections to the mean-field theory. It turns out that repulsive forces increase the pressure at fix...

System-adapted correlation energy density functionals from effective pair interactions

This article discusses some ideas concerning an ‘average-pair-density functional theory’, in which the ground-state energy of a many-electron system is rewritten as a functional of the spherically and system-averaged pair density. These ideas are further clarified with simple physical examples. Then it is shown that the proposed formalism can be combined with density functional theory to build ...