Dr. Lin H. Yang
LLNL
"Quantum -based simulations
of material strength and phase diagrams for high-Z metals"
Quantum level simulations using molecular dynamics (MD) and molecular
statics (MS) techniques have played a key role in our understanding of
material strength and phase stability at high pressure and temperature.
However, earlier quantum-based theoretical framework for obtaining
high-pressure phase diagrams and multiphase equations of state (EOS)
for high-Z metals treats cold, ion-thermal, and electron-thermal
contributions to phase stability and the EOS separately. In particular,
the ion-thermal component is calculated for zero-temperature electrons
via temperature-independent interatomic potentials. For d- and
f-electron metals, however, there can be a high density of electronic
states at the Fermi level, leading to a strong coupling between the
ion- and electron-thermal components for temperatures as low as melt.
This effectively leads to temperature-dependent forces on the ions.
Consequently, the high-temperature phase diagram and EOS, the melt
curve, and the liquid EOS can all be significantly affected. To treat
the electrons and ions on an equal footing we are using rigorous ab
initio quantum-molecular-dynamics (QMD) simulations for d- and
f-electron metals, so the additional ion-electron coupling and
temperature-dependent forces in question are rigorously treated. The
main goals of this talk are: (i) to present robust classical and
quantum MD algorithms to treat d- and f-electron metals at high
pressure; (ii) to study pressure-dependent material strength; (iii) to
study important physical phenomena, including defects, and liquid
structure for suitable prototype metals such as Mo and U; and (iv) to
propose a scheme to construct the corresponding temperature-dependent
interatomic potentials for such metals that accurately describe the
temperature-dependent forces.
This work was supported under the auspices of the U.S. Department of
Energy by the University of California Lawrence Livermore National
Laboratory under Contract No. W-7405-ENG-48.
Thursday May 6, 2004
4:10 p.m., 416 Phy/Geo