Accuracy of the diffusion quantum Monte Carlo method on dissociation curves of van der Waals systems with the...

Non-covalent interactions, particularly van der Waals (vdW) interactions, are crucial in chemistry, physics, and life sciences. Accurate calculation of both the repulsive and attractive parts of vdW potentials is essential for a reliable description of dissociation curves in vdW systems. The diffuse quantum Monte Carlo (DMC) method is known to be able to calculate vdW interactions accurately at equilibrium distances. However, its performance on vdW interaction energies at non-equilibrium distances has not been investigated. In this work, dissociation curves for ten vdW interacting systems with dispersion interactions, dipole-induced dipole interactions and dipole-dipole interactions are calculated using the DMC and some low-level methods, i.e., MP2 and CCSD, to illustrate their accuracy for the attractive and repulsion potentials of vdW potentials. Our results indicate that while MP2 and CCSD provide reliable descriptions of the attractive potential in vdW interactions, they exhibit larger errors in the repulsive region. On the other hand, DMC employing a single-Slater-Jastrow trial wavefunction with the DLA approximation for the non-local part of pseudopotentials demonstrates high accuracy in both repulsive and attractive potentials. Additionally, reliable DMC results can be achieved with T-moves if the Jastrow factor is optimized carefully. These results emphasize the capability of the DMC with DLA to accurately compute vdW interaction energies at non-equilibrium distances.