Discontinuous transition of molecular-hydrogen chain to the quasi-atomic state: Exact diagonalization - ab initio approach

TL;DR

This paper presents a rigorous method combining exact diagonalization and ab initio adjustments to study a discontinuous transition in hydrogen chains from molecular to quasi-atomic states, highlighting the importance of electron correlations.

Contribution

It introduces an original approach that avoids double-counting issues and captures the discontinuous transition in hydrogen chains using a combined exact diagonalization and ab initio method.

Findings

The transition is strongly discontinuous even for short chains.

The transition involves a sudden change in intramolecular distance.

The transition relates to the Mott-Hubbard insulator-metal transition.

Abstract

We obtain in a direct and rigorous manner a transition from a stable molecular hydrogen $nH_2$ single chain to the quasiatomic two-chain $2nH$ state. We devise an original method composed of an exact diagonalization in the Fock space combined with an ab initio adjustment of the single-particle wave function in the correlated state. In this approach the well-known problem of double-counting the interparticle interaction does not arise at all. The transition is strongly discontinuous, and appears even for relatively short chains possible to tackle, $n=3\div6$. The signature of the transition as a function of applied force is a discontinuous change of the equilibrium intramolecular distance. The corresponding change of the Hubbard ratio $U/W$ reflects the Mott--Hubbard-transition aspect of the atomization. Universal feature of the transition relation to the Mott criterion for the insulator--metal transition is also noted. The role of the electron correlations is thus shown to be of fundamental significance.