Normal-Mode Analysis for Intra- and Intermolecular Electron–Phonon Coupled Systems with Charge-Ordered and Dimer–Mott Ground States

Abstract

We have theoretically studied the ground-state properties of the molecular compound, Et2Me2Sb[Pd(dmit)2]2, which shows a dimer–Mott character in Pd(dmit)2 layers at high temperature and a charge order mainly stabilized by an electron–phonon interaction at low temperature. An effective extended Peierls–Hubbard model is constructed with intra- and intermolecular electronic and phonon degrees of freedom. Using mean-field approximation, the energies and optimized structures are calculated for isolated neutral, monovalent, divalent Pd(dmit)2 dimers and their two-dimensional crystallized states. The optical conductivities of the crystallized states are calculated by a single-configuration interaction method. For intramolecular vibrations, normal-mode analysis is performed, which is useful to explain the recent experimental results. Molecular vibrations with different symmetries are coupled to different combinations of electrons and holes within a molecule, so that their frequencies depend on the molecular charg...