PRESSURE CALCULATION IN MOLECULAR-DYNAMICS SIMULATIONS OF MOLECULAR-CRYSTALS

In molecular dynamics simulations the pressure is usually calculated w ith molecules as basic units. This approach fails for a polymer, and i t is shown that pressure calculation on the basis of individual atoms is equally well possible, even though the forces on the atoms are not pair-additive. The only disadvantage is the need for a larger pressure time constant in simulations where the volume is adjusted to an exter nal pressure. The formalism is tested on the alpha-D-glucose monohydra te crystal. Some comments are made on the calculation of the temperatu re in the leap-frog scheme.