Comprehensive $ab$ $initio$ investigation of the phase diagram of quasi-one-dimensional molecular solids

TL;DR

This study uses first-principles calculations and advanced Monte Carlo methods to map the phase diagram of TM$_2$X molecular solids, revealing how material-dependent Coulomb interactions influence charge and spin orderings.

Contribution

It provides a comprehensive ab initio analysis of the phase diagram of TM$_2$X compounds, integrating Hamiltonian derivation with variational Monte Carlo to elucidate ordering phenomena.

Findings

Material-dependent Coulomb interactions govern charge and spin orderings.

The correlation effect is characterized by the ratio of screened Coulomb interaction to transfer integrals.

The phase diagram reveals distinct symmetry-breaking phases depending on material parameters.

Abstract

An $ab$ $initio$ investigation of the family of molecular compounds TM$_2$$X$ is conducted, where TM is either TMTSF or TMTTF and $X$ takes centrosymmetric monovalent anions. By deriving the extended Hubbard-type Hamiltonians from first-principles band calculations and evaluating not only the intermolecular transfer integrals but also the Coulomb parameters, we discuss their material dependence in the unified phase diagram. Furthermore, we apply the many-variable variational Monte Carlo method to accurately determine the symmetry-breaking phase transitions, and show the development of the charge and spin orderings. We show that the material-dependent parameter can be taken as the correlation effect, represented by the value of the screened on-site Coulomb interaction $U$ relative to the intrachain transfer integrals, for the comprehensive understanding of the spin and charge ordering in this system.