HR: 16:15h
AN: MR34A-02    [Abstracts]
TI: First-principles thermoelasticity of hexagonal-close-packed iron at high pressures
AU: * Sha, X
EM: x.sha@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch RD, NW, Washington, DC 20015 United States
AU: Cohen, R E
EM: cohen@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch RD, NW, Washington, DC 20015 United States
AB: We performed first-principles linear response quasi-harmonic lattice dynamics computations as well as particle-in-cell (PIC) (Wasserman, et cal. PRB 53, 8296, 1996) calculations using the full-potential Linear-Muffin-Tin-Orbital (LMTO) method (Savrasov, PRB 54, 16470, 1996) to understand and predict the lattice dynamical, thermal equation of state and elastic properties of hexagonal-close-packed (hcp) iron at high temperatures and high pressures. The phonon dispersion and phonon density of states have been calculated at different volumes and various c/a axial ratios, and agree well with available experimental data. We derived the Helmholtz free energy functional, and found that the calculated geometric mean phonon frequencies and free energies from the two different methods agree well for hcp Fe under pressure, contrary to Gannarelli et al. (PEPI 139, 243, 2005). We have performed detailed investigations on the behavior of elastic constants and various thermal equation of state parameters, such as the bulk modulus, the thermal expansion coefficient, the Anderson-Gruneisen parameter, the Gruneisen ratio, and the heat capacity as functions of temperature and pressure. The results generally agree with available experiment and an an earlier theoretical calculation (Steinle-Neumann et al. Nature 413, 57, 2001), except that we do not find large changes in c/a with T. Nevertheless, we find similar thermal effects on the elastic constants as predicted earlier. This work was supported by US Department of Energy ASC subcontract to Caltech, Grant DOE W-7405-ENG-48.
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3949 Thermal expansivity
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005