Comparison of the Coulomb and non-orthogonal approaches to the construction of the exciton Hamiltonian

Abstract

A description for systems consisting of many different interacting fragments is one of the most prominent problems in computational chemistry. When excited states of such systems are considered, the exciton Hamiltonian method is generally used, where the total supramolecular Hamiltonian is constructed based on the wavefunctions of the fragments. In the current study, we compare two non-orthogonal methods to calculate intermolecular interactions (exciton couplings): non-orthogonal product approach and local orbital configuration interaction with transition density cumulative atomic multipole moments and direct QM calculation for the model systems. The methods are used to determine the role of exchange and overlap components of interaction. We have shown that both of these components are not essential even when the distance between interacting molecules is short. Charge-transfer states played an important role to accurately calculate the excited states energies.