Unified phase diagram of models exhibiting neutral-ionic transition

TL;DR

This paper presents a comprehensive phase diagram for models of neutral-ionic transitions in organic compounds, unifying previous models and providing detailed numerical insights into their behavior.

Contribution

A new unified model for neutral-ionic transitions is developed, connecting earlier models and enabling detailed numerical analysis using DMRG.

Findings

Unified phase diagram of neutral-ionic transition models

Numerical calculations of excitation gaps and ionicity

Identification of phase boundaries and order parameters

Abstract

We have studied the neutral-ionic transition in organic mixed-stack compounds. A unified model has been derived which, in limiting cases, is equivalent to the models proposed earlier, the donor-acceptor model and the ionic Hubbard model. Detailed numerical calculations have been performed on this unified model with the help of the density-matrix renormalization-group (DMRG) procedure calculating excitation gaps, ionicity, lattice site entropy, two-site entropy, and the dimer order parameter on long chains and the unified phase diagram has been determined.