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.