Showing papers by "Ernest R. Davidson published in 2004"

Energies of isoelectronic atomic ions from a successful metageneralized gradient approximation and other density functionals

Abstract: We show that the poor performance of approximate Kohn-Sham (KS) density functional theory for highly charged atomic ions is improved dramatically by ensuring that (i) the exchange functional recovers the correct leading term in the $Z$ expansion of the exchange energy ($Z$ is the nuclear charge) and (ii) the correlation functional is bounded under uniform scaling of the density to the high-density limit---i.e., ${\mathrm{lim}}_{\ensuremath{\lambda}\ensuremath{\rightarrow}\ensuremath{\infty}}{E}_{\mathrm{c}}^{\mathrm{KS}}[{n}_{\ensuremath{\lambda}}]g\ensuremath{-}\ensuremath{\infty}$, where ${n}_{\ensuremath{\lambda}}(\mathbf{r})={\ensuremath{\lambda}}^{3}n(\ensuremath{\lambda}\mathbf{r})$. The performance of several density functionals (BLYP, BP86, VS98, HCTH/407, PBE, PKZB, and TPSS) is compared for the 4-, 10-, and 18-electron atomic series spanning values of $Z$ from 4 to 28. Especially accurate results are obtained with the nonempirical metageneralized gradient approximation of Tao, Perdew, Staroverov, and Scuseria (TPSS). High-$Z$ limits of selected exchange and correlation functionals are evaluated and compared with the exact values.

Bonding in FHF−, (HF)2, and FHF

Abstract: Bonding in FHF−, (HF)2, and FHF is compared from the molecular orbital and electrostatic bonding viewpoint. The electrostatic force is dominant in the formation of FHF− and HF dimer. Exchange repulsion dominates in preventing the formation of FHF and leads to a D∞h transition state for H exchange. At the D∞h stationary points for FHF− and FHF the electronic structure can be understood using delocalized symmetry orbitals, but this delocalization is not the primary driving force along the potential energy surface leading to these structures. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004