Self-energy-functional theory

TL;DR

Self-energy-functional theory provides a unified, non-perturbative variational framework for approximating strongly correlated electron systems, connecting various cluster mean-field methods within a path-integral formalism.

Contribution

It introduces a general variational principle based on the self-energy functional, unifying and deriving cluster mean-field approximations like VCA and cluster DMFT.

Findings

Derivation of cluster mean-field approximations from the variational principle

Discussion of relationships and consistency among different methods

Framework applicable to strongly correlated lattice models

Abstract

Self-energy-functional theory is a formal framework which allows to derive non-perturbative and thermodynamically consistent approximations for lattice models of strongly correlated electrons from a general dynamical variational principle. The construction of the self-energy functional and the corresponding variational principle is developed within the path-integral formalism. Different cluster mean-field approximations, like the variational cluster approximation and cluster extensions of dynamical mean-field theory are derived in this context and their mutual relationship and internal consistency are discussed.