David A. Liberman

Theory and experiment for ultrahigh pressure shock Hugoniots

Abstract Several equation of state models for hot, dense matter are compared with experimental data for the shock Hugoniots of beryllium, aluminum, iron, copper, and molybdenum up to extreme pressures. The best models are in good agreement with experiment and with one another, suggesting that our understanding of dense, partially ionized matter is good.

A deficiency of local density functionals for the calculation of self-consistent field atomic data in plasmas

Abstract In generating the atomic data base used in computing opacities of hot dense plasmas the local density functional approximation (LDA) is often employed. One advantage of the LDA is that the configuration average energy of a large number of ionization states and excited configurations can be computed compactly using a multi-variate Taylor series expansion in occupation numbers. The pitfalls of employing a local density functional and its impact on the quality of the Taylor series approximation are discussed. The consequences of modeling opacities with a LDA are illustrated by comparisons with experiment. A method for obviating the problems inherent in the LDA is presented.

Calculations of photoabsorption by atoms using a linear response method

We have made extensive calculations of photoabsorption by all neutral atoms from hydrogen to lawrencium for photon energies up to one kilovolt. Our method was the relativistic time-dependent local density approximation with the usual configuration average for open shells. The most important collective effects are included through an induced field. Expected features such as resonant photoemission and autionization are seen. Examples of the calculations will be shown. The computer program used is available from the Computer Physics Communications Program Library.

Dense plasma equation of state model

Abstract Low density models of atoms in plasmas use isolated ion data plus a uniform electron gas correction (usually called continuum lowering) to arrive at new energy levels. When levels pass into the continuum they become resonances—then broaden and diminish in strength. At high plasma densities the energy levels require further correction, and an estimate of the effective level degeneracy is needed. We describe our model of these effects and show results for low temperature gold plasmas in the density range 10 -4 to 10 +3 g⧸cc.

Insights on the plasma polarization shift: A comparison of local density approximation and optimum potential methods

Abstract The plasma polarization shift computed with a local density functional approximation of an ion-sphere model is compared with results calculated using an optimum central field effective exchange potential. Indications are that the bulk of the shift is an artifact of the approximate exchange functional describing the interaction between bound and continuum orbitals in the LDA.

On the distribution of bound levels of ions in dense plasmas: The plasma polarization shift

Abstract We present a reconciliation of the null experimental observations with a proper statistical treatment of the plasma polarization shift, the density dependent shift of spectral lines which results from the differential screening of bound electron orbitals by penetrating, neutralizing free electrons in dense plasmas. It turns out that even at otherwise very high electron densities the mean number of perturbing free electrons within bound quantum orbitals of plasma ions is only fractional. Thus most radiators actually experience no perturbation and are expected to emit/absorb unshifted. On the other hand, the strength of the resulting central feature can be significantly reduced with respect to that of unperturbed radiators because of the power shifted into the dim red-side wing.

Finite density effects in plasmas

Abstract The electronic structure on an ion in a low-density plasma is compared with that of an ion in a high-density plasma. The raising of energy levels and pressure ionization of loosely bound levels are well known and easy to estimate with reasonable accuracy. The accompanying changes in dipole transition rates—the main point of this note—are illustrated by means of self-consistent field calculations of an isolated ion and an ion screened by free electrons.

Modified exchange potential for local density calculations of atoms

The local density exchange potential which is used in most atomic calculations is based on the degenerate electron gas. It is proposed that it should be augmented by a term that has the correct large radius behaviour and which contains an adjustable parameter. The parameter is determined by minimizing the total energy. Better calculations of several physical quantities are obtained.