Derivation of the Supermolecular Interaction Energy from the Monomer Densities in the Density Functional Theory

TL;DR

This paper derives the supermolecular interaction energy in density functional theory directly from monomer densities, providing a rigorous and accurate computational approach validated on various molecular dimers.

Contribution

It introduces a new method to compute interaction energies from monomer densities in DFT, maintaining orthogonality via the Pauli blockade, and demonstrates high accuracy with standard functionals.

Findings

Interaction energies agree within 0.1% of standard calculations

Method validated on van der Waals and hydrogen-bonded dimers

Applicable to multiple common DFT functionals

Abstract

The density functional theory (DFT) interaction energy of a dimer is rigorously derived from the monomer densities. To this end, the supermolecular energy bifunctional is formulated in terms of mutually orthogonal sets of orbitals of the constituent monomers. The orthogonality condition is preserved in the solution of the Kohn-Sham equations through the Pauli blockade method. Numerical implementation of the method provides interaction energies which agree with those obtained from standard supermolecular calculations within less than 0.1% error for three example functionals: Slater-Dirac, PBE0 and B3LYP, and for two model van der Waals dimers: Ne2 and (C2H4)2, and two model H-bond complexes: (HF)2 and (NH3)2.