A Parallel Quantum Mechanical MD Simulation of Liquids

A parallel implementation to perform quantum molecular dynamics simulations of liquids on Born-Oppenheimer surfaces is evaluated. The MD method allows the use of atomic energy gradient forces at an arbitrary level of quantum chemical methodology and electronic state. The computational scheme is very simple to implement, although still expensive to use. The method can easily be developed further for studies which are beyond the capabilities of current classical simulations, e.g., simple chemical reactions or other chemical processes involving excited electronic states or radicals. In a preliminary study, the approach is applied to simulate liquid water (with all internal degrees of freedom included) at the semi-empirical AM 1 molecular orbital (MO), and at the ab initio SCF-MO Hartree-Fock level. Performance, scaling and load balancing properties of the parallel scheme are discussed. Timings of an implementation on an IBM SP-2 are presented. To test the approach, the simulation results are compared with those obtained from corresponding classical simulations of water, from simulations using the Car-Parrinello method and to experimental radial distribution functions.