Development of nonlocal kinetic-energy density functional for the hybrid QM/MM interaction

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.

Automated summary

This work focuses on the development of a nonlocal kinetic-energy functional based on the response function for molecular systems, which enables the use of orbital-free density-functional theory (OF-DFT) in the hybrid QM/MM method. It differs from previous functionals that rely on the homogeneous electron gas as a reference for the response function. Benchmark tests on a QM water molecule in a dimer system and in a condensed environment show that our approach can adequately reproduce the energetics and polarization density of the QM solute under the influence of the MM environment. This suggests the potential ability of the kinetic-energy functional based on response functions for molecular reference systems.