MOLECULAR-DYNAMICS AT CONSTANT TEMPERATURE AND PRESSURE

Algorithms for molecular dynamics (MD) at constant temperature and pre ssure are investigated. The ability to remain in a regular orbit in an intermittent chaotic regime is used as a criterion for long-time stab ility. A simple time-centered algorithm (leap frog) is found to be the most stable of the commonly used algorithms in MD. A model of N one-d imensional dimers with a double-well intramolecular potential, for whi ch the distribution functions at constant temperature T and pressure P can be calculated, is used to investigate MD-NPT dynamics. A time-cen tered NPT algorithm is found to sample correctly and to be very robust with respect to volume scaling.