Quantum Simulations in Metals

Our current quantum-based theoretical framework for obtaining high-pressure phase diagrams and multiphase equations of state (EOS) for 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 developing 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 project are: (i) to develop robust QMD algorithms to treat d- and f-electron metals at high pressure; (ii) to study important physical phenomena, including high-temperature phase stability, melting, and liquid structure for suitable prototype metals such as Mo and U; and (iii) to develop corresponding temperature-dependent MGPT interatomic potentials for such metals that accurately describe the temperature-dependent forces. To reach higher temperatures and larger numbers of atoms in QMD simulations, new linearly scaling Spectral Quadrature ^[3] and quadratically scaling Discontinuous Galerkin ^[4] electronic structure methods are being developed.