Molecular dynamics simulations of fluid methane properties using ab initio intermolecular interaction potentials.

Area of Science:

• Computational chemistry
• Physical chemistry
• Chemical physics

Background:

• Accurate intermolecular potentials are crucial for simulating fluid properties.
• Previous models for methane interactions lacked sufficient accuracy for detailed simulations.

Purpose of the Study:

• To compute high-accuracy intermolecular interaction energies for the methane dimer.
• To construct an *ab initio* potential energy surface (PES) for molecular dynamics (MD) simulations.
• To validate the PES by comparing simulation results with experimental data for fluid methane.

Main Methods:

• Calculated potential curves for 12 methane dimer conformations using second-order Møller-Plesset perturbation theory (MP2) with counterpoise correction.
• Employed large basis sets (Pople and Dunning) and performed coupled cluster with single and double and perturbative triple excitations [CCSD(T)] calculations for calibration.
• Extrapolated MP2 potentials to the complete basis set (CBS) limit and fitted the data to a 4-site potential model.

Main Results:

• MP2 binding curves showed significant anisotropy based on dimer orientation.
• The fitted 4-site potential model explained dimer stability through hydrogen-hydrogen repulsion.
• MD simulations using the *ab initio* PES accurately reproduced experimental radial distribution functions and self-diffusion coefficients.

Conclusions:

• The developed *ab initio* PES provides a highly accurate representation of methane dimer interactions.
• The PES enables reliable molecular dynamics simulations of fluid methane properties.
• This work advances the understanding of intermolecular forces in methane systems.