Dynamical variational principles for strongly correlated electron systems

TL;DR

This paper discusses the self-energy-functional approach (SFA) for strongly correlated electron systems, highlighting its theoretical foundations, approximation strategies, and connections to other methods like density-functional theory and dynamical mean-field theory.

Contribution

It provides a comprehensive analysis of the SFA's formal structure, compares it with static and dynamical variational principles, and explores its potential for developing new non-perturbative approximations.

Findings

Elucidates the formal analogy between static and dynamical variational approaches.

Highlights the strengths and limitations of the SFA.

Suggests future directions for non-perturbative approximation development.

Abstract

The self-energy-functional approach (SFA) is discussed in the context of different variational principles for strongly correlated electron systems. Formal analogies between static and dynamical variational approaches, different types of approximation strategies and the relations to density-functional and dynamical mean-field theory are emphasized. The discussion elucidates the strengths of the SFA in the construction of new non-perturbative approximations but also the limitations of the approach and thereby opens up future perspectives.