Ensemble density-functional theory for ab-initio molecular dynamics of metals and finite-temperature insulators

TL;DR

This paper introduces a novel ensemble density-functional theory approach for efficient ab-initio molecular dynamics simulations of metals and insulators at finite temperatures, ensuring stability and invariance under orbital transformations.

Contribution

It develops a matrix-based projected free energy functional that simplifies simulations and guarantees the Liouville equation, enabling stable and efficient molecular dynamics.

Findings

Efficient variational minimization algorithm for variable occupancy systems

Invariant free energy functional under orbital unitary transformations

Applicable to metals and finite-temperature insulators

Abstract

A new method is presented for performing first-principles molecular-dynamics simulations of systems with variable occupancies. We adopt a matrix representation for the one-particle statistical operator Gamma, to introduce a ``projected'' free energy functional G that depends on the Kohn-Sham orbitals only and that is invariant under their unitary transformations. The Liouville equation [ Gamma , H ] = 0 is always satisfied, guaranteeing a very efficient and stable variational minimization algorithm that can be extended to non-conventional entropic formulations or fictitious thermal distributions.