Nonlocal Subsystem Density Functional Theory

TL;DR

This paper introduces fully nonlocal non-additive kinetic energy functionals into subsystem DFT, significantly improving accuracy for strongly interacting systems and resolving previous issues with overly attractive interaction energies.

Contribution

It presents the first implementation of fully nonlocal NAKEs in subsystem DFT, enhancing the method's applicability to systems with high inter-subsystem electron density overlap.

Findings

Nonlocal NAKEs improve interaction energy accuracy.

Enhanced electron density predictions over GGA NAKEs.

Resolved the issue of overly attractive interaction energy curves.

Abstract

By invoking a divide-and-conquer strategy, subsystem DFT dramatically reduces the computational cost of large-scale, \textit{ab-initio} electronic structure simulations of molecules and materials. The central ingredient setting subsystem DFT apart from Kohn-Sham DFT is the non-additive kinetic energy functional (NAKE). Currently employed NAKEs are at most semilocal (i.e., they only depend on the electron density and its gradient), and as a result of this approximation, so far only systems composed of weakly interacting subsystems have been successfully tackled. In this work, we advance the state-of-the-art by introducing fully nonlocal NAKEs in subsystem DFT simulations for the first time. A benchmark analysis based on the S22-5 test set shows that nonlocal NAKEs considerably improve the computed interaction energies and electron density compared to commonly employed GGA NAKEs, especially when the inter-subsystem electron density overlap is high. Most importantly, we resolve the long standing problem of too attractive interaction energy curves typically resulting from the use of GGA NAKEs.