Optimized constant pressure stochastic dynamics

A recently proposed method for computer simulations in the isothermal-isoba ric (NPT) ensemble, based on Langevin-type equations of motion for the part icle coordinates and the "piston" degree of freedom, is rederived by straig htforward application of the standard Kramers-Moyal formalism. An integrati on scheme is developed that reduces to a time-reversible symplectic integra tor in the limit of vanishing friction. This algorithm is hence expected to be quite stable for small friction, allowing for a large time step. We dis cuss the optimal choice of parameters, and present some numerical test resu lts. (C) 1999 American Institute of Physics. [S0021-9606(99)50434-0].