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

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.

Orbital-Free Density Functional Theory: An Attractive Electronic Structure Method for Large-Scale First-Principles Simulations

“…The result was one GGA KEDF and one nonlocal KEDF with a density-independent kernel . The other is by Takahashi. − It is based on direct employment of the inverted KS response functions computed by a post conventional KS-DFT calculation of the KS response function. Initial results provide accurate but nontransferable functionals.…”

“…The KS response function therefore is transformed as χ s ( r , r ′) → χ s (ε, ε′ ), a form which can be handled more efficiently for inversion. In ref , the inversion is handled instead by a spectral representation of the response function. Once χ s –1 is obtained, approximations for the non-interacting kinetic energy and its derivative are formulated as an expansion around a reference density, n 0 ( r ).…”

“…Following eq where δn = n – n 0 . Even though the results in refs − seem encouraging, the approach needs further exploration and the underlying approximations need to be characterized and delineated more clearly before it can be considered viable for broad applicability.…”

“…Another interesting approach − develops two strategies to obtain inverse KS response functions to be used to define KEDFs and their functional derivatives. The strategies differ in the way the response functions are represented.…”

“…Following eq T s [ n ] ≃ T s [ n 0 ] + prefix∫ d boldr v T s ( r ) δ n ( r ) + 1 2 ∫ d boldr d boldr ′ δ n ( r ) χ s − 1 ( r , r ′ ) δ n ( r ′ ) where δn = n – n 0 . Even though the results in refs − seem encouraging, the approach needs further exploration and the underlying approximations need to be characterized and delineated more clearly before it can be considered viable for broad applicability.…”