We are in the process of updating and extending the OPAL equation-of-state (EOS) and opacity data to include low-mass stars. The EOS part of that effort now is complete, and the results are described herein. The new data cover main-sequence stars having mass � 0.1 M� . As a result of the more extreme matter conditions encountered with low-mass stars, we have added new physics. The electrons are now treated as relativistic, and we have improved our treatment of molecules. We also consider the implications of the new results for helioseismology.

http://iopscience.iop.org/article/10.1086/341894/pdf

Updated and Expanded OPAL Equation-of-State Tables: Implications for Helioseismology

Molecular-beam experiments have exposed a new wealth of detail on the general reaction ${A}^{*}+B\ensuremath{\rightarrow}A+{B}^{+}+{e}^{\ensuremath{-}}$ first suggested by Penning in 1927. The new capabilities not available to traditional swarm techniques include mass and electron spectroscopy on the reaction products and angle-resolved measurements of the scattering of both reagents and products. These new results have stimulated the recent development of both the electronic structure and the dynamical theories necessary for a first-principles description of at least the simplest of these reactions, those involving small atomic and diatomic species $B$. Recent progress in both experiment and interpretation is critically reviewed, and the prospects for attaining a global understanding of Penning ionization in larger systems are assessed.

Molecular-beam studies of Penning ionization

Optical potential stabilisation method for predicting resonance levels

It has been shown recently that dynamical correlation effects can be adequately described by using an electron-gas expression for correlation between electrons of different spins. In this paper the method is applied to the calculation of excitation energies for the first- and second-row atoms and to the determination of ground-state properties for small polyatomic molecules, such as CH2, CH4, CH
 4
 +
 , CH
 5
 +
 . Additionally, deficiencies of the method for cases with few electrons and strongly varying electron density are investigated and an empirical correction to the electron-gas approximation is proposed. This correction is based on atomic data and gives an overall improvement for test molecules with two to four electrons.

Correlation energies in the spin-density functional formalism

A simple, yet reliable, scheme based on treating uniformly singlet-pair and triplet-pair interactions is suggested to extrapolate atomic and molecular electron correlation energies calculated at two basis-set levels of ab initio theory to the infinite one-electron basis-set limit. The novel dual-level method is first tested on extrapolating the full correlation in single-reference coupled-cluster singles and doubles energies for the closed-shell systems CH2(A11), H2O, HF, N2, CO, Ne, and F2 with correlation-consistent basis sets of the type cc-pVXZ (X=D,T,Q,5,6) reported by Klopper [Mol. Phys. 6, 481 (2001)] against his own benchmark calculations with large uncontracted basis sets obtained from explicit correlated singles and doubles coupled-cluster theory. Comparisons are also reported for the same data set but using both single-reference Moller-Plesset and coupled-cluster doubles methods. The results show a similar, often better, accordance with the target results than Klopper’s extrapolations where sin...

Extrapolating to the one-electron basis-set limit in electronic structure calculations

The ground state energy of HeH+ has been calculated in the Born—Oppenheimer approximation for 0.9 ⩽ R ⩽ 4.5 au by using an 83-term variational wavefunction in elliptic coordinates and including the interelectronic distance. The resulting potential curve has been used to compute the quasibound state spectrum of the ion.

W. Kołos

Papers

New ab initio potential curve and quasibound states of HeH