Development of Nonlocal Kinetic-Energy Density Functional for the Hybrid QM/MM Interaction

TL;DR

This paper develops a nonlocal kinetic-energy density functional for orbital-free DFT to improve hybrid QM/MM simulations, accurately reproducing energetics and polarization in molecular systems.

Contribution

It introduces a novel response-function-based nonlocal kinetic-energy functional for OF-DFT in QM/MM methods, contrasting with previous homogeneous electron gas-based functionals.

Findings

Accurately reproduces QM solute energetics in MM environments.

Successfully models polarization density in molecular systems.

Demonstrates potential of response-function-based kinetic-energy functionals.

Abstract

Development of the electronic kinetic-energy density functional is a subject of major interest in theoretical physics and chemistry. In this work, the nonlocal kinetic-energy functional is developed in terms of the response function for the molecular system to realize the orbital free density-functional theory(OF-DFT) to be utilized in the hybrid QM/MM(quantum mechanical/molecular mechanical) method. The present approach shows a clear contrast to the previous functionals where the homogeneous electron gas serves as a reference to build the response function. As a benchmark test we apply the method to a QM water molecule in a dimer system and that embedded in a condensed environment to make comparisons with the results given by the QM/MM calculations employing the Kohn-Sham DFT. It was found that the energetics and the polarization density of the QM solute under the influence of the MM environment can be adequately reproduced with our approach. This work suggests the potential ability of the kinetic-energy functional based on the response functions for the molecular reference systems.