Rubidium at high pressure and temperature

In the present paper we report theoretical calculations for the Hugoniot of shock-compressed rubidium. We use an all-electron full-potential method ba sed on density-functional theory to obtain the total energy, pressure and e lectronic density of states. Thermal contributions to the equation of state (EOS) were introduced through temperature dependent occupation of the elec tronic states and a Gruneisen model was used for determining the nuclear th ermal motion, The calculated Hugoniot is in very good agreement with the sh ock experiments. A temperature of about 10 000 K is reached at the pressure of about 300 kbar, the highest reached experimentally. Rubidium was chosen for this study because it undergoes a sequence of unusual pressure-induced structural transitions which have been attributed to s-d electron transfer . Since most studies of s-d transfer have been carried out at temperatures below 500 K, Little is known of how it effects the equation of state at ver y high temperature. We found that the predicted Rb Hugoniot is very sensiti ve to the thermal s-d electron transfer, which leads to a considerable lowe ring of the predicted Hugoniot pressure and temperature.