Fixed-Node Diffusion Monte Carlo of Lithium Systems

TL;DR

This paper applies fixed-node diffusion Monte Carlo to various lithium systems, achieving high accuracy in total energies and quantifying fixed-node errors by testing multiple orbital sets without pseudo potentials.

Contribution

It provides a comprehensive analysis of fixed-node errors in lithium systems using DMC with various orbitals, avoiding pseudo potentials for improved accuracy.

Findings

Achieves 97-99% of correlation energy in lithium systems.

Demonstrates high accuracy of fixed-node DMC across different lithium structures.

Quantifies fixed-node errors by comparing multiple orbital sets.

Abstract

We study lithium systems over a range of number of atoms, e.g., atomic anion, dimer, metallic cluster, and body-centered cubic crystal by the diffusion Monte Carlo method. The calculations include both core and valence electrons in order to avoid any possible impact by pseudo potentials. The focus of the study is the fixed-node errors, and for that purpose we test several orbital sets in order to provide the most accurate nodal hyper surfaces. We compare our results to other high accuracy calculations wherever available and to experimental results so as to quantify the the fixed-node errors. The results for these Li systems show that fixed-node quantum Monte Carlo achieves remarkably high accuracy total energies and recovers 97-99 % of the correlation energy.