Lawrence Livermore National Laboratory



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.

A snapshot of a QMD simulation of liquid uranium at high temperature and pressure.

A snapshot of a QMD simulation of liquid uranium (U) at high temperature and pressure. The goal of these simulations is to collect accurate data so one can develop corresponding temperature-dependent MGPT interatomic potentials that accurately describe the temperature-dependent forces. The spheres indicate positions of ions and the corresponding isosurfaces representing the electron charge density.

Recent Publications

  1. "Quantum-Mechanical Interatomic Potentials with Electron Temperature for Strong-Coupling Transition Metals", J. A. Moriarty, R. Q. Hood, and L. H. Yang, Phys. Rev. Lett. 108, 036401 (2012).
  2. "Quantum Molecular Dynamics Simulations of Uranium at High Pressure and Temperature ", R.Q. Hood, L.H. Yang, and J. A. Moriarty, Phys. Rev. B 78, 024116 (2008).
  3. "Spectral Quadrature method for accurate O(N) electronic structure calculations of metals and insulators," P.P. Pratapa, P. Suryanarayana, and J.E. Pask, Comput. Phys. Commun. 200, 96-107 (2016).
  4. "Adaptive local basis set for Kohn-Sham density functional theory in a discontinuous Galerkin framework II: Force, vibration, and molecular dynamics calculations," G. Zhang, L. Lin, W. Hu, C. Yang, and J.E. Pask, submitted, 2015. arXiv: 1510.06489

Maintained by   Randolph Q. Hood