Advanced gradientlike methods for rigid-body molecular dynamics

A novel approach is developed to integrate the equations of motion in many-body systems of interacting rigid polyatomic molecules. It is based on an advanced gradientlike decomposition technique in the presence of translational and orientational degrees of freedom. As a result, a new class of reversible phase-space volume preserving fourth-order algorithms for rotational motion is introduced. Contrary to standard nongradient decomposition integrators, the algorithms derived take into account additional analytically integrable terms in the exponential propagators, while the arising gradients are expressed in terms of forces and torques. This allows one to increase significantly the precision of the integration and, at the same time, reduce the increased computational costs. The optimized second-order integrator is also presented. The gradientlike and optimized algorithms are tested in molecular dynamics simulations of water versus well-established integrators known previously. It is shown that the new algorithms lead to the best efficiency in the rigid-body integration. (C) American Institute of Physics.