Metal-Insulator Transition described by Natural Orbital Functional Theory

TL;DR

This paper demonstrates that Natural Orbital Functional Theory effectively models the metal-insulator transition in hydrogen clusters, accurately predicting critical distances and capturing strong correlation effects beyond mean-field methods.

Contribution

The study applies NOFT to hydrogen clusters to accurately describe the MIT, providing a reliable approach for modeling strong electronic correlations in condensed matter systems.

Findings

NOFT captures the MIT transition as interatomic distance decreases.

Estimated critical distance rc ~ 1.2 Angstroms agrees with quantum Monte Carlo results.

NOFT reliably describes strong correlation effects in large-scale models.

Abstract

The metal-insulator transition (MIT) is a fundamental phenomenon in condensed matter physics and a hallmark of strong electronic correlations. Hydrogen-based systems offer a simple yet powerful model for investigating the MIT, as their insulating behavior arises purely from electron-electron interactions. In this work, we study finite hydrogen clusters with cubic geometries using Natural Orbital Functional Theory (NOFT), a method capable of accurately describing correlated systems beyond mean-field approaches. We focus on two key signatures of the MIT: the fundamental energy gap and the harmonic average of the atomic one-particle reduced density matrix. Our results show that NOFT captures the transition from insulating to metallic behavior as the interatomic distance decreases. By extrapolating the energy gap to the thermodynamic limit, we estimate a critical distance rc ~ 1.2 Ang, in excellent agreement with quantum Monte Carlo benchmarks. These findings demonstrate the reliability of NOFT for describing strong correlation effects in large-scale models.