Diffusion Monte Carlo and PIMD calculations of radial distribution functions using an updated CCSD(T) potential for CH₅⁺

Abstract

We report a new permutationally invariant polynomial (PIP) fit to CCSD(T)/aug-cc-pVTZ energies for ${\text{CH}}_5^{+}$ that provides fast analytical forces, unlike the original PIP fit of 2006. The new fit, which is slightly more precise than the previous one, is used in classical molecular dynamics, diffusion Monte Carlo and path integral molecular dynamics calculations of CH and HH radial distribution functions (RDFs) at temperatures of 10 and $50\text{K}$. Corresponding RDFs are also reported for ${\text{CD}}_3{\text{H}}_2^{+}$. The well-known quantum localisation of the H atoms to the diatomic site from previous and present DMC calculations is maintained at $10\text{K}$ but shows additional delocalisation to the ‘${\text{CH}}_3^{+}$’ site at $50\text{K}$.

GRAPHICAL ABSTRACT

Keywords:

• Potential surface
• diffusion Monte Carlo
• ${\text{CH}}_5^{+}$
• PIMD

Acknowledgments

We dedicate this paper to the memory of Timothy Lee.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

JMB and PP acknowledge support from NASA-ARA [grant 80NSSC22K1167].