Quantum corrections and the computer simulation of molecular fluids

Abstract

The quantum corrections to the free energy, to order h ², are obtained for a fluid of rigid interacting molecules in a form suitable for use in computer simulation. The result involves only the mean squared force on a molecule and the components of the mean squared torque about the principal molecular axes which are, or ought to be, routinely evaluated in simulations. The corrections are found to be small, but not insignificant, especially for molecules with one or more low principal moments of inertia. It is suggested that such corrections should be routinely included in reports of computer simulations of rigid-molecule fluids. The corrections are illustrated for liquid nitrogen, fluorine, chlorine, hydrogen chloride and methane.