Melting Line, Structural and Dynamic Properties of Warm Dense Hydrogen at High Pressures: Atomistic Simulation

A hydrogen melting line in the pressure range from 50 to 500 GPa was obtained using the molecular dynamics method with the DeePMD neural network potential. The obtained results are in good agreement with experimental and theoretical data. Pair correlation functions and vibrational spectra of various phases have been analyzed. A jump in electrical conductivity has been detected when crossing the melting line. This effect is more noticeable in the molecular phase, manifesting itself in a sharp increase in conductivity by six orders of magnitude during the formation of a molecular fluid, whereas a threefold decrease in conductivity has been observed during the melting of a metallic crystal of atomic hydrogen. The results obtained make it possible to refine the parameters of the phase transformations of dense hydrogen in the ultrahigh pressure region.