Multiple time scale molecular dynamics for fluids with orientational degrees of freedom. II. Canonical and isokinetic ensembles

We have developed several multiple time stepping techniques to overcome the limitations on efficiency of molecular dynamics simulations of complex fluids. They include the modified canonical and isokinetic schemes, as well as the extended isokinetic Nos\ue9-Hoover chain approach. The latter generalizes the method of Minary, Tuckerman, and Martyna for translational motion [Phys. Rev. Lett. 93, 150201 (2004)]10.1103/PhysRevLett.93.150201 to systems with both translational and orientational degrees of freedom. Although the microcanonical integrators are restricted to relatively small outer time steps of order of 16fs, we show on the basis of molecular dynamics simulations of ambient water that in the canonical and isokinetic thermostats the size of these steps can be increased to 50 and 75fs, respectively (at the same inner time step of 4fs). Within the generalized isokinetic Nos\ue9-Hoover chain algorithm we have derived, huge outer time steps of order of 500fs can be used without losing numerical stability and affecting equilibrium properties \ua9 2011 Canadian crown.Peer reviewed: YesNRC publication: Ye