Linear and Non-linear Susceptibilities from Diffusion Quantum Monte Carlo: Application to Periodic Hydrogen Chains

TL;DR

This paper uses diffusion quantum Monte Carlo to accurately compute linear and non-linear susceptibilities of periodic hydrogen chains, highlighting the importance of exchange effects and electronic correlations.

Contribution

It introduces a method to calculate susceptibilities from polarization changes using a Berry-phase functional within diffusion quantum Monte Carlo.

Findings

Calculated susceptibilities agree with quantum chemistry estimates.

Exchange effects are crucial for accurate susceptibilities.

Electronic correlations significantly influence second hyper-susceptibilities.

Abstract

We calculate the linear and non-linear susceptibilities of periodic longitudinal chains of hydrogen dimers with different bond-length alternations using a diffusion quantum Monte Carlo approach. These quantities are derived from the changes in electronic polarization as a function of applied finite electric field - an approach we recently introduced and made possible by the use of a Berry-phase, many-body electric-enthalpy functional. Calculated susceptibilities and hyper-susceptibilities are found to be in excellent agreement with the best estimates available from quantum chemistry - usually extrapolations to the infinite-chain limit of calculations for chains of finite length. It is found that while exchange effects dominate the proper description of the susceptibilities, second hyper-susceptibilities are greatly affected by electronic correlations. We also assess how different approximations to the nodal surface of the many-body wavefunction affect the accuracy of the calculated susceptibilities.