Determination of screened Coulomb repulsion energies in organic molecular crystals: A real space approach

TL;DR

This paper introduces a real space method to calculate screened Coulomb interaction parameters in organic molecular crystals, aiding the development of accurate Hubbard models for correlated organic materials.

Contribution

The authors present a novel real space approach to determine screened Coulomb parameters by modeling molecules with distributed polarizabilities, improving accuracy in molecular crystal simulations.

Findings

Method accurately predicts Coulomb screening in TTF-TCNQ

Splitting intra- and inter-molecular screening enhances model precision

Real space approach is computationally efficient and versatile

Abstract

We present a general method for determining screened Coulomb parameters in molecular assemblies, in particular organic molecular crystals. This allows us to calculate the interaction parameters used in a generalized Hubbard model description of correlated organic materials. In such a model only the electrons in levels close to the Fermi level are included explicitly, while the effect of all other electrons is included as a renormalization of the model parameters. For the Coulomb integrals this renormalization is mainly due to screening. For molecular materials we can split the screening into intra- and inter-molecular screening. Here we demonstrate how the inter-molecular screening can be calculated by modeling the molecules by distributed point-polarizabilities and solving the resulting self-consistent electrostatic screening problem in real space. For the example of the quasi one-dimensional molecular metal TTF-TCNQ we demonstrate that the method gives remarkably accurate results.