Treatment of intershell correlation effects in a b i n i t i o calculations by use of core polarization potentials. Method and application to alkali and alkaline earth atoms

Abstract

In the present approach the high reliability of ab initio techniques is combined with the easily amenable phenomenological core polarization concept for an efficient treatment of intershell correlation effects in all-electron SCF and valence CI calculations. By use of only a single adjustable atomic parameter, which is related to the radius of the core and determines the cutoff at short range, our effective core polarization potential (CPP) accounts quantitatively for dynamical intershell correlation as well as exclusion effects on the correlation energy of the core. The applications refer to alkali and alkaline earth atoms (Li to K and Be to Ca) and a detailed analysis is performed for core polarization effects on ionization energies, electron affinities, oscillator strengths, polarizabilities, van der Waals coefficients, the valence electron density, and spin densities. Very accurate results are obtained for well-known energetic properties and spin densities at the nucleus. With respect to the other applications we consider our results as the most reliable to date with an estimated uncertainty of 1%–2%.

Smooth relativistic Hartree–Fock pseudopotentials for H to Ba and Lu to Hg

“…Moreover, core-valence correlation can be included within correlated wave function calculations performed with HF pseudopotentials by using core polarization potentials. 6,7,8 Core polarization potentials mimic the effects of dynamical polarization of the core by the valence electrons, as well as static polarization effects due to the other ions. We would therefore like to use HF pseudopotentials in our DMC calculations, preferably constructed from Dirac-Fock (DF) theory in order to include the relativistic effects which are significant for heavy atoms.…”

Ground- and excited-state properties of the polar and paramagnetic RbSr molecule: A comparative study

“…It is based on the representation of the Rb + and Sr 2+ ionic cores by relativistic effective core potential (ECP) complemented with core polarization potential (CPP) simulating core-valence correlation along the lines developed by Müller and Meyer [52,53] and Foucrault et al [54].These effective potentials involve semi-empirical parameters (reported in Ref. [18]) which are chosen to reproduce the energies of the lowest s, p and d levels of the Rb and Sr + one-valence-electron systems.…”

Potential energy surface of the 12A′ Li2 + Li doublet ground state

“…This form of the cutoff parameter was first presented by Müller et al [27] and produces good agreement for ground and low excited states, however it does show diminished results for Rydberg states [27]. Our calculations using this core polarization potential to describe the core valence correlation energy were done using the MOLPRO 2008.1 [22] implementation of the Fuentealba et al [26] CPP.…”