EQUATION OF STATE OF ALKANES .2.

The pressure in condensed fluids of pentane and decane is calculated b y molecular dynamics for temperatures from room temperature to 673 K a nd pressures up to 350 MPa using the anisotropic united atom (AUA) mod el [Toxvaerd, J. Chem. Phys. 93, 4290 (1990)], and compared with other recently published united atom models (UA). The pressure for the AUA model agrees well with experimentally obtained pressures whereas the U A model fails outside the region of moderate pressure and density. The impact of the torsion potential and the intermolecular potential on s tructure, thermodynamics, and self-diffusion is investigated for fluid s of decanes at high and moderate densities. A time reversible and num erical stable implementation of Gauss' principle of least constraint ( of bond lengths) is described in the Appendix. The constrained molecul ar dynamics is performed without any adjustment or rescaling of the bo nd lengths. (C) 1997 American Institute of Physics.