Comparison of the accuracy of approximate methods TrESP and TrCAMM for evaluation of pigment coupling in light-harvesting complexes

Abstract

Due to the large size of light-harvesting complexes, approximate methods are commonly used for calculating the coupling energies between their constituents. Two approximate methods are studied in this work: TrESP and the recently suggested TrCAMM method, based on the expansion of the one-particle density matrix. The quality of approximation of the electrostatic potential in the framework of these two approaches has been compared for two biological pigments as an example—chlorophyll a and bacteriochlorophyll a. It has been shown that both approaches provide high accuracy of approximation of the matrix elements of the electrostatic potential operator. In addition, it has been demonstrated that symmetrization of the one-particle density matrix in the framework of the TrCAMM method significantly improves the calculation accuracy and makes the computational procedure unambiguous.