Accuracy of Noncovalent Interactions Involving d-Elements by the 1-Determinant Fixed-Node Diffusion Monte Carlo...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Materials Science

Background:

• Accurate prediction of noncovalent interactions is crucial for understanding chemical systems.
• Effective core potentials (ECPs) simplify calculations by treating core electrons implicitly.
• Diffusion Quantum Monte Carlo (FNDMC) is a powerful method for electronic structure calculations.

Purpose of the Study:

• To critically assess the accuracy of ECP-based single-determinant FNDMC for d-element systems.
• To identify and analyze sources of bias in FNDMC calculations involving d-elements.
• To provide practical guidance for using FNDMC with ECPs in these systems.

Main Methods:

• Utilized single-determinant fixed-node diffusion quantum Monte Carlo (SD FNDMC).
• Employed effective core potentials (ECPs) for d-element systems.
• Compared results against a reliable coupled-cluster CCSD(T)/CBS reference.

Main Results:

• SD FNDMC exhibited substantial biases in interaction energy differences for HCu:HCu and HCu:CuH systems, exceeding 2% relative error.
• The primary error source was identified as the higher nuclear charge (Z) of d-group atoms compared to sp elements.
• Bias in SD FNDMC correlates with increased electronic densities and higher nuclear charges.

Conclusions:

• SD FNDMC with ECPs requires cautious application for systems containing d-elements, especially those with high nuclear charges.
• The method's accuracy is compromised by the electronic environment around d-group atoms.
• Further methodological improvements may be needed for reliable FNDMC calculations in these challenging systems.