Multi-Orbital Molecular Compound (TTM-TTP)I_3: Effective Model and Fragment Decomposition

TL;DR

This study develops an effective two-orbital Hubbard model for (TTM-TTP)I_3, revealing its low-energy electronic structure and intra-molecular charge ordering through ab initio calculations and fragment decomposition, confirming the fragment model's validity.

Contribution

The paper introduces a detailed effective model and fragment decomposition approach for (TTM-TTP)I_3, connecting ab initio results with a simplified ladder model for the first time.

Findings

The tight-binding band structure matches density functional theory results.

The molecule can be modeled as a two-leg ladder based on fragment decomposition.

Inter-fragment Coulomb energies scale inversely with distance.

Abstract

The electronic structure of the molecular compound (TTM-TTP)I_3, which exhibits a peculiar intra-molecular charge ordering, has been studied using multi-configuration ab initio calculations. First we derive an effective Hubbard-type model based on the molecular orbitals (MOs) of TTM-TTP; we set up a two-orbital Hamiltonian for the two MOs near the Fermi energy and determine its full parameters: the transfer integrals, the Coulomb and exchange interactions. The tight-binding band structure obtained from these transfer integrals is consistent with the result of the direct band calculation based on density functional theory. Then, by decomposing the frontier MOs into two parts, i.e., fragments, we find that the stacked TTM-TTP molecules can be described by a two-leg ladder model, while the inter-fragment Coulomb energies are scaled to the inverse of their distances. This result indicates that the fragment picture that we proposed earlier [M.-L. Bonnet et al.: J. Chem. Phys. 132 (2010) 214705] successfully describes the low-energy properties of this compound.