Exact Constraint of Density Functional Approximations at the Semiclassical Limit

TL;DR

This paper explores the semiclassical limit of electronic systems to evaluate density functional approximations, revealing their divergence issues and proposing insights for developing improved functionals for strongly correlated systems.

Contribution

It introduces the semiclassical limit in electronic systems, links it to strong correlation challenges, and analyzes the divergence of mainstream density functional approximations.

Findings

Mainstream DFAs diverge as 7 ightarrow 0, violating finite energy constraints.

Semiclassical analysis explains underestimated DFA energies in transition-metal molecules.

The approach offers a pathway to develop better density functionals for strongly correlated systems.

Abstract

We introduce the semiclassical limit to electronic systems by taking the limit $\hbar\rightarrow 0$ in the solution of Schr\"odinger equations. We show that this limit is closely related to one type of strong correlation that is particularly challenging from conventional multi-configurational perspective but can be readily described through semiclassical analysis. Furthermore, by studying the performance of density functional approximations (DFAs) in the semiclassical limit, we find that mainstream DFAs have erroneous divergent energy behaviors as $\hbar \rightarrow 0$, violating the exact constraint of finite energy. Importantly, by making connection of the significantly underestimated DFA energies of many strongly correlated transition-metal diatomic molecules to their rather small estimated $\hbar_{\text{eff}}$, we demonstrate the usefulness of our semiclassical analysis and its promise for inspiring better DFAs.