Showing papers by "Ernest R. Davidson published in 1998"
70 citations
TL;DR: In this article, the vertical excitation or ionization energy of the observed spectrum was derived for the V-N transition of ethylene, which gave 7.8 eV and 10.73 eV, respectively.
65 citations
TL;DR: In this article, a technique for reducing computational effort in multireference second-order perturbation theory with very large complete active space (CAS) SCF reference functions is proposed.
35 citations
TL;DR: In this paper, the effects of 3Σ/1Σ mixing in the analysis of the observed ESR spectral results for these three isotopomers in all four rare gas hosts were investigated and a theoretical model was developed that treated these spin-pairs as weakly interacting atoms.
Abstract: The H⋯H, H⋯D, and D⋯D spin-pair radicals have been thoroughly investigated in neon, argon, krypton, and xenon matrices near 4 K by electron spin resonance (ESR). A theoretical model has been developed that treats these spin-pairs as weakly interacting atoms. The model includes the effects of 3Σ/1Σ mixing in the analysis of the observed ESR spectral results and yields a consistent set of magnetic parameters for these three isotopomers in all four rare gas hosts. The consideration of H atoms interacting with other H atoms over a distribution of internuclear distances in the rare gas lattice is included in the theoretical and experimental analyses. Application of the model to earlier ESR results for H⋯CH3 reveals a value for its Heisenberg exchange interaction (J) which is found to be considerably larger than that for the H⋯H spin-pair. The effects of methane and neon on the J value are calculated for these spin-pairs. The H⋯H case is unusual in that the nuclear hyperfine interaction (A) is considerably larg...
31 citations
TL;DR: In this paper, the effects of electron correlation on the valence binding energy spectrum were investigated using multi-reference singles and doubles configuration interaction calculations of the full ion-neutral overlap distributions.
27 citations
TL;DR: In this paper, the behavior of unrestricted Moller−Plesset (UMP) for the case where the spin along the up-down dilation axis was examined for the Singleton Dirac.
Abstract: The unrestricted Hartree−Fock UHF method is often advocated for “singlet” diradicals. Here, we examine the behavior of unrestricted Moller−Plesset (UMP) for the case where the spin along the “up” d...
24 citations
TL;DR: In this article, the performance of commonly used correlation and exchange correlation functionals for highly charged atomic ions has been compared with exact nonrelativistic energies of atomic species with 2-18 electrons for nuclei from Z 2 He to Z 26 Ni.
Abstract: The performance of commonly used correlation and exchange-correlation functionals has been studied for highly charged atomic ions. Calculated energies have been compared with exact nonrelativistic energies of atomic species with 2–18 electrons for nuclei from Z 2 He to Z 26 Ni . It is found that all density functionals considered here reveal problems in the description of correlation effects as a function of nuclear charge Z. S1050-2947 98 09309-3
23 citations
TL;DR: In this paper, the results of applying a variety of methods (CASSCF, PUHF, MUMP2, DFT, UDFT, and CI) for obtaining reliable potential energy surfaces for diradicals were reported.
20 citations
TL;DR: In this paper, the authors confirmed the existence of a peak at 12.7 eV binding energy which was observed by Baltzer et al. in the synchrotron photoelectron spectra of C3H4 and perdeuterated allene (C3D4).
18 citations