HR: 0800h
AN: DI41A-0346    [Abstracts]
TI: Lattice Dynamics and Thermal Equation of State of Platinum
AU: * Sun, T
EM: tsun@grad.physics.sunysb.edu
AF: Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, United States
AU: Umemoto, K
EM: umemoto@cems.umn.edu
AF: Department of Chemical Engineering and Materials Science, and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455, United States
AU: Wu, Z
EM: wuz@cems.umn.edu
AF: Department of Chemical Engineering and Materials Science, and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455, United States
AU: Zheng, J
EM: jczheng@bnl.gov
AF: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, United States
AU: Wentzcovitch, R
EM: wentzcov@cems.umn.edu
AF: Department of Chemical Engineering and Materials Science, and Minnesota Supercomputer Institute, University of Minnesota, Minneapolis, MN 55455, United States
AB: Platinum is widely used as a pressure calibration standard for in situ high-pressure and high-temperature experiments. However, the isothermal EOS reduced from shock Hugoniot has uncertainties. It appears that it seriously overestimates pressure in the high pressure range. This has also been suggested by recent DAC experiments. We use density functional theory to calculate the thermal equation of state of platinum, up to 600 GPa and 5000K. The static lattice energy is computed by using the LAPW method, with LDA, PBE, and the recently proposed WC functional. The electronic thermal free energy is evaluated using the Mermin functional. The vibrational part is computed within the quasi-harmonic approximation using density functional perturbation theory and pseudopotentials. Special attention is paid to the influence of the electronic temperature to the phonon frequencies. A theoretical Hugoniot is obtained by solving the Rankine-Hugoniot equation. We find that in overall LDA results agree best with the experimental ones, while the new WC functional shows much improved results than PBE. After correcting the calculated equilibrium volume to the experimental one, the room temperature isothermal EOS agrees with the new DAC data, and confirms that the previous standard overestimates pressure. The calculated thermodynamic properties agree reasonably well with experiments. We further compare our thermal EOS with the previous ones based on empirical models. Research supported by NSF/EAR and NSF/ITR
DE: 3919 Equations of state
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting