Spin dependent force model of molecular liquids: Theory and simple applications

We introduce a spin dependent force model for molecular liquids, in which the force between two atoms depends both on the interatomic separation distance and internal, quantum degrees of freedom. In this paper we introduce an additional approximation and treat the internal degrees of freedom semiclassically. We explore some simple properties of this model applied to hydrogen atoms and molecules. Using input from quantum chemistry calculations for the electronic potential energy surfaces, we calculate an effective molecule–molecule potential energy and the dynamics of two and three atom systems. We also perform molecular dynamic simulations which propagate both position and internal ‘‘spin’’ degrees of freedom.