James D. Johnson

Global equation of state for copper

A new, tabular (SESAME format) equation of state for Cu, suitable for use in hydrodynamic simulations, is described and compared to experimental data. Pressures, internal energies, and Helmholtz free energies are tabulated as functions of temperature and density. The new equation of state builds on the theoretical investigations of Greeff, et al., (J. Phys. Chem. Solids 67, 2033 (2006)), but extends the range of densities and temperatures covered to 10-5-105 g/cc and 0-108K. The staticlattice cold curve is modeled using the semi-empirical stabilized jellium equation near ambient densities, LDA and GGA density-functional predictions at moderate compressions, and Thomas- Fermi-Dirac theory at high compressions. The Johnson ionic model, which smoothly interpolates between Debye-like and ideal-gas behavior, is employed to model contributions from atomic motion, and Thomas-Fermi-Dirac theory is used for contributions from thermal electronic excitations. Predictions for the compressibility, principle and porous...

Perturbation theory calculation of the pressure for an electron–ion system

By means of finite-temperature, many-body perturbation theory we derive through order e4 the corrections to an ideal Fermi gas plus an ideal Maxwell–Boltzmann gas of ions. This computation is carried out for general values of the de Broglie density. The behavior of these coefficients is reported, and their implications for the ionization profile at low densities are described.

Testing of a Liquid Equation of State Model Against Copper Data

We model the free energy of a liquid near melting by postulating that ΔSV, the entropy difference between solid and liquid at fixed volume, is independent of pressure, and that the melting curve follows the Lindemann law. Using a solid free energy determined from ab initio phonon frequencies, we apply these assumptions to liquid Cu. We show that they are consistent with the Hugoniot sound speed data. We investigate the consequences of typical variations of ΔSV for shock melting. We also investigate models for the shear modulus and the longitudinal sound speed.

High Accuracy Equations of State for Standards

We discuss the development of accurate equations of state by combining electronic structure theory for the lattice vibrations and electronic excitations with an empirical static lattice electronic energy (cold curve). We present applications to the fcc metals Cu, Au, and Pt. We discuss the status of pressure standards.