Molecular dynamics simulations of mixed hard-core/continuous potentials: Algorithms and application

Many model molecular interactions of theoretical and practical importance are mixtures of hard-core (discontinuous)/continuous potentials. However, dynamical simulation studies of such systems have been greatly hindered by the lack of a viable molecular-dynamics simulation algorithms. We develop and apply, a set of second-order, time-reversible algorithms for constant energy (NVE) and constant temperature (NVT) molecular-dynamics (MD) simulation of systems with mixed hard-core/continuous potentials. The NVE method, which we call Collision Verlet, is constructed using operator splitting techniques similar to those that have been used successfully to generate a variety molecular-dynamics integrators. The five NVT algorithms that we present, are generated by combining real-time Nosé thermostats with Collision Verlet. One is based on the Nosé-Hoover equations of motion and four are based on the Nosé-Poincare real-time formulation of Nosé dynamics. In addition, we use one of the four Nosé-Poincare algorithms to calculate diffusion constants in model fluids consisting of hard spheres with an attractive inverse-sixth-power continuous potential.