London dispersion forces without density distortion: a path to first principles inclusion in density functional theory

Abstract

We analyse a path to construct density functionals for the dispersion interaction energy from an expression in terms of the ground state densities and exchange–correlation holes of the isolated fragments. The expression is based on a constrained search formalism for a supramolecular wavefunction that is forced to leave the diagonal of the many-body density matrix of each fragment unchanged, and is exact for the interaction between one-electron densities. We discuss several aspects: the necessary features of a density functional approximation for the exchange–correlation holes of the monomers, the optimal choice of the one-electron basis (named “dispersals”), and the functional derivative with respect to monomer density variations.