Equation of state of alkanes II

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Abstract
The pressure in condensed fluids of pentane and decane is calculated by molecular dynamics for temperatures from room temperature to 673 K and pressures up to 350 MPa using the anisotropic united atom (AUA) model [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 UA model fails outside the region of moderate pressure and density. The impact of the torsion potential and the intermolecular potential on structure, thermodynamics, and self-diffusion is investigated for fluids of decanes at high and moderate densities. A time reversible and numerical stable implementation of Gauss’ principle of least constraint (of bond lengths) is described in the Appendix. The constrained molecular dynamics is performed without any adjustment or rescaling of the bond lengths.