Quantum chemical exploration of the HCl dimer interaction

Abstract

Quantum chemical calculations based on the MP2 perturbation method with a large basis set are used to determine a pointwise representation of the HCl dimer interaction at equilibrium bondlengths. A series of intermolecular potentials are then fitted to the quantum chemical data with the aim of exploring the convergence in accuracy with increasing complexity in the functional forms. Beginning with simple Lennard-Jones potentials with electrostatics added we progress to more complex functional forms based on distributed multipole approximation and anisotropic representations of exchange repulsion and polarisation. Pitfalls in the fitting procedure are discussed, and convergence is monitored by examination of second virial coefficient data, the structure of the stationary points and spectroscopic parameters.