Linear and nonlinear susceptibilities from diffusion quantum Monte Carlo: application to periodic hydrogen chains

Area of Science:

• Computational physics
• Quantum chemistry
• Materials science

Background:

• Accurate calculation of electronic polarization is crucial for understanding material optical properties.
• Previous methods often rely on extrapolations, introducing uncertainties.
• Developing robust theoretical frameworks for nonlinear optical properties is an ongoing challenge.

Purpose of the Study:

• To compute linear and nonlinear susceptibilities of periodic hydrogen dimer chains.
• To investigate the impact of bond-length alternation on these properties.
• To assess the accuracy of a novel many-body electric-enthalpy functional approach.

Main Methods:

• Diffusion quantum Monte Carlo (DQMC) calculations.
• Application of a Berry-phase, many-body electric-enthalpy functional.
• Finite electric field perturbation to derive polarization changes.

Main Results:

• Calculated susceptibilities and hypersusceptibilities show excellent agreement with high-level quantum chemistry estimates.
• Exchange effects are dominant for susceptibilities, while correlations significantly influence second hypersusceptibilities.
• The nodal surface approximation in DQMC affects the accuracy of susceptibility calculations.

Conclusions:

• The employed DQMC approach with the electric-enthalpy functional provides a reliable method for calculating optical properties.
• Electronic correlations play a vital role in higher-order nonlinear optical responses.
• Approximations in the many-body wave function's nodal surface require careful consideration for precise results.