Hybridizing pseudo-Hamiltonians and non-local pseudopotentials in diffusion Monte Carlo

Area of Science:

• Computational Quantum Chemistry
• Materials Science
• Atomic and Molecular Physics

Background:

• Accurate treatment of effective core potentials (ECPs) is crucial for continuum quantum Monte Carlo (QMC) methods.
• Existing non-local (NL) pseudopotentials with localization approximations introduce moderate residual errors in QMC studies.
• These errors impact the accuracy of molecular and solid-state applications.

Purpose of the Study:

• To introduce a novel approach for treating ECPs in QMC methods by hybridizing non-local potentials and pseudo-Hamiltonians.
• To reduce residual non-locality and localization errors in existing ECPs.
• To demonstrate the improved accuracy of these hybrid potentials for 3d elements.

Main Methods:

• Development of a method to recast pseudopotentials for 3d elements into hybrid pseudo-Hamiltonians.
• Utilizing diffusion Monte Carlo (DMC) to calculate atomic ionization potentials (Ti, Fe) and molecular binding properties (TiO, FeO).
• Analysis of localization errors by examining DMC energy changes with respect to localization approximations for elements Sc-Zn.

Main Results:

• The proposed hybrid potentials successfully reduce localization errors compared to potentials with identical non-local channels.
• Demonstrated fidelity in predicting ionization potentials of Ti and Fe, and binding properties of TiO and FeO molecules.
• Localization error reduction is proportional to the reduced non-local energy without a Jastrow factor; this effect diminishes with increased d-shell filling when a Jastrow is used.

Conclusions:

• A subset of existing ECPs can be reformulated into the hybrid pseudo-Hamiltonian form to mitigate DMC localization errors.
• The study highlights the potential for further error reduction by developing ECPs directly within this hybrid framework.
• This approach offers a pathway to more accurate QMC calculations for systems involving 3d elements.