  We present the first quantum molecular dynamics calculation of zero-pressure
isobar of solid and liquid uranium that account for spin-orbit coupling. We
demonstrate that inclusion of spin-orbit interaction leads to higher degree of
the thermal expansion of uranium, especially in the liquid phase. Full
accounting of relativistic effects for valence electrons, particularly
spin-orbital splitting of the 5f band, is substantial for the reproduction of
the experimental density of molten uranium at the melting temperature.
Influence of the spin-orbit interaction on the thermodynamic properties at high
temperatures and pressures is also analyzed.
