Measure-preserving and time-reversible integration algorithms for constant temperature molecular dynamics.

Abstract

This thesis concerns the formulation of integration algorithms for non-Hamiltonian molecular dynamics simulation at constant temperature. In particular, the constant temperature dynamics of the Nosé-Hoover, Nosé-Hoover chain, and Bulgac-Kusnezov thermostats are studied. In all cases, the equilibrium statistical mechanics and the integration algorithms have been formulated using non-Hamiltonian brackets in phase space. A systematic approach has been followed in deriving numerically stable and efficient algorithms. Starting from a set of equations of motion, time-reversible algorithms have been formulated through the time-symmetric Trotter factorization of the Liouville propagator. Such a time-symmetric factorization can be combined with the underlying non- Hamiltonian bracket-structure of the Liouville operator, preserving the measure of phase space. In this latter case, algorithms that are both time-reversible and measure-preserving can be obtained. Constant temperature simulations of low-dimensional harmonic systems have been performed in order to illustrate the accuracy and the efficiency of the algorithms presented in this thesis.