The pressure and pressure tensor for macromolecular systems

The calculation of pressure for macromolecular systems using atom and molecule representations are discussed. We derive the force and pressure tensor due to angle and dihedral angle potentials using an approach which makes the mathematics involved simpler than currently available in the literature. By using this approach, the derivation of the second-derivative matrix elements for the torsional energy can also be simplified. We show that the angle and torsional angle forces do not contribute to the pressure; however, they do contribute to the pressure tensor in general.