SIMPLE REVERSIBLE MOLECULAR-DYNAMICS ALGORITHMS FOR NOSE-HOOVER CHAINDYNAMICS

Reversible algorithms for Nod-Hoover chain (NHC) dynamics are develope d by simple extensions of Verlet-type algorithms: leap frog, position Verlet, and velocity Verlet. Tests for a model one dimensional harmoni c oscillator show that they generate proper canonical distributions an d are stable even with a large time step. Using these algorithms, the effects of the Nose mass and chain length are examined. For a chain le ngth of two, the sampling efficiency is much more sensitive to the Nos e mass than for a longer chain of length four. This indicates that the chain length in general should be longer than two. The noniterative n ature of the algorithms allows them to be easily adapted for constrain t dynamics. For the most general case where multiple NHC's are coupled to a system with constraints, a correction of the first Nose accelera tion is required, which is derived from the continuity equation on a c onstrained hypersurface of the phase space. Tests for model systems of two and three coupled harmonic oscillators with one normal mode const rained show that these algorithms, in combination with the corrected d ynamical equations, sample the canonical distributions for the unconst rained degrees of freedom. (C) 1997 American Institute of Physics.