LEAPFROG ROTATIONAL ALGORITHMS FOR LINEAR-MOLECULES

A study is made of four algorithms which integrate the rotational equa tions of motion for rigid linear molecules. They are leapfrog algorith ms in the sense that the quantities saved between time steps are the o n-step orientation and the mid-step angular velocity. Thermostatted ve rsions of the algorithms as well as conventional energy-conserving ver sions are described. The algorithms are extensively tested in simulati ons of liquid nitrogen, the aim being to study the effect of increased time steps on a range of measured properties. The most successful alg orithm, based on applying a length constraint to the axis vector, show s remarkable stability and can be used with very large time steps.