How Important is Orbital Choice in Single-Determinant Diffusion Quantum Monte Carlo Calculations?

Area of Science:

• Computational Chemistry
• Quantum Many-Body Physics

Background:

• The accuracy of fixed-node diffusion quantum Monte Carlo (FN-DMC) energies depends on the nodal surface.
• The choice of orbitals used to define this nodal surface is critical.

Purpose of the Study:

• To systematically compare the quality of FN-DMC energies.
• To evaluate nodal surfaces derived from different orbital types: Hartree-Fock, B3LYP, and LDA.

Main Methods:

• Fixed-node diffusion quantum Monte Carlo (FN-DMC) calculations.
• Systematic comparison of FN-DMC energies for atoms and diatomic molecules.
• Utilizing nodal surfaces from single determinants of Hartree-Fock, B3LYP, and LDA orbitals.

Main Results:

• Kohn-Sham orbitals (from B3LYP and LDA) yield significantly improved FN-DMC atomization energies compared to Hartree-Fock orbitals.
• The study analyzes the impact of spin contamination on orbital quality and subsequent FN-DMC energy accuracy.

Conclusions:

• Kohn-Sham orbitals offer a superior basis for defining nodal surfaces in FN-DMC.
• This finding enhances the accuracy of quantum chemical calculations for molecular systems.