Atomic simulation of shock compressed liquid helium

A molecular dynamics simulation has been performed to investigate the Hugon iot equation-of-state (EOS) and the corresponding radial distribution funct ion (RDF) of liquid helium at high temperatures and densities. The calculat ed Hugoniot EOS is well in agreement with the experiments given by Nellis e t al., and the corresponding RDFs show distinct peak or peaks due to the mo st probable nearest-neighbor packing, though the matter being studied is li quid. A single nearest-neighbor peak appears in the lower pressure regime, but two peaks, including a newly second-nearest-neighbor peak besides the f ormer one, emerges when the shock state goes up around T = 1.2 x 10(4) K an d the density rho = 0.409 g/cm(3), demonstrating a higher-order transition of a disorder-order one for the second-nearest-neighbor structure. (C) 1999 Elsevier Science B.V. All rights reserved.