Importance of High Angular-Momentum Channels in Pseudopotentials for Quantum Monte Carlo

TL;DR

This paper demonstrates that including high angular-momentum channels in pseudopotentials significantly improves the accuracy of Quantum Monte Carlo calculations for condensed systems, reducing errors in total energies.

Contribution

It introduces the importance of incorporating high angular-momentum channels in pseudopotentials to enhance Quantum Monte Carlo accuracy, especially for excited states.

Findings

Including high angular-momentum channels reduces energy errors by several eV.

Proper choice of the local channel is crucial for accuracy.

Adding these channels does not significantly increase computational cost.

Abstract

Quantum Monte Carlo methods provide in principle an accurate treatment of the many-body problem of the ground and excited states of condensed systems. In practice, however, uncontrolled errors such as those arising from the fixed-node and pseudopotential approximations often limit the quality of results. We show that the accuracy of quantum Monte Carlo calculations is limited by using available pseudopotentials. In particular, it is necessary to include angular momentum channels in the pseudopotential for excited angular momentum states and to choose the local channel appropriately to obtain accurate results. Variational and diffusion Monte Carlo calculations for Zn, O, and Si atoms and ions demonstrate that these issues can affect total energies by up to several eV for common pseudopotentials. Adding higher-angular momentum channels into the pseudopotential description reduces such errors drastically without a significant increase in computational cost.