Constructing a Non-additive Non-interacting Kinetic Energy Functional Approximation for Covalent Bonds from Exact Conditions

TL;DR

This paper introduces a new non-additive kinetic energy functional approximation for covalent bonds that combines the von Weizs"acker and Thomas-Fermi functionals, improving accuracy in P-DFT calculations.

Contribution

A novel covalent approximation for NAKE that satisfies exact constraints and outperforms existing methods near equilibrium and stretched bonds.

Findings

Highly accurate NAKE for stretched bonds

Outperforms standard approximations near equilibrium

Enables fast, accurate P-DFT calculations

Abstract

We present a non-decomposable approximation for the non-additive non-interacting kinetic energy (NAKE) for covalent bonds based on the exact behavior of the von Weizs\"{a}cker (vW) functional in regions dominated by one orbital. This covalent approximation (CA) seamlessly combines the vW and the Thomas-Fermi (TF) functional with a switching function of the fragment densities constructed to satisfy exact constraints. It also makes use of ensembles and fractionally-occupied spin-orbitals to yield highly accurate NAKE for stretched bonds while outperforming other standard NAKE approximations near equilibrium bond lengths. We tested the CA within Partition-Density Functional Theory (P-DFT) and demonstrated its potential to enable fast and accurate P-DFT calculations.