Rigid body molecular dynamics with nonholonomic constraints: Molecular thermostat algorithms

Generalized Euler equations and center of mass equations are derived to des cribe the motion of a rigid body under general nonholonomic constraints. Th ese equations provide a basis for developing algorithms for rigid body mole cular dynamics (MD) simulations with nonholonomic constraints. In particula r, two distinct molecular thermostat algorithms for constant temperature ri gid body MD simulations are described. Both algorithms ensure satisfaction of the temperature constraint at every MD time step, without introducing ad ditional numerical errors into the center of mass velocities or angular vel ocities. Results from constant temperature MD simulations of a system of 50 0 methylene chloride (CH2Cl2) rigid molecules using both thermostats are pr esented, exhibiting their efficiency and accuracy. finally, a generalized G auss's principle of least constraint is derived, to establish a formal conn ection between the molecular approach described hers for incorporating nonh olonomic constraints in MD simulations and previous atomistic approaches.