Showing papers by "Ernest R. Davidson published in 1977"
567 citations
TL;DR: In this paper, a new formula for correcting double-excitation Cl result for the effects of higher excitations is suggested, and the correct form of the effective hamiltonian for a coupled-electron-pair-approximation is discussed for a dilute gas of helium atoms.
536 citations
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TL;DR: In this article, the 1π,π* state of ethylene has been thoroughly investigated at the configuration interaction level utilizing an extensive basis set and a configuration selection scheme which emphasizes a correct description of all correlation effects involving the π or π* electrons.
Abstract: The 1(π,π*) state of ethylene has been thoroughly investigated at the configuration interaction level utilizing an extensive basis set and a configuration selection scheme which emphasizes a correct description of all correlation effects involving the π or π* electrons. The result, contrary to the Hartree–Fock prediction, but in agreement with the general experimental conclusion, is a mostly valence state as indicated by a value for 〈π*‖x2‖π*〉 of 8.8 a.u. using the π* natural orbital. A calculated excitation energy of 7.96 eV is in reasonable agreement with the 7.65 eV experimental absorption maximum. It is found that σ→σ* excitations relative to the ground state are essential to describe the left–right correlation of σ electrons with the π* electron. This in turn compensates for the ionic πA 2–πB 2 nature of the 1(π,π*) state, allowing the SCF state to become contracted at the CI level. The π* orbital in the second 1(π,π*) state appears to be well characterized at a CI level as a 3d orbital constrained t...
109 citations
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63 citations
TL;DR: In this paper, a configuration interaction scheme was employed to calculate all n=3 Rydberg states of ethylene derived from the excitation of a π electron, which was designed to account for the small amount of correlation energy of the Ryberg electron and facilitate calculation of term values from a corresponding calculation on the positive ion.
Abstract: A configuration interaction scheme is employed to calculate all n=3 Rydberg states of ethylene derived from the excitation of a π electron. This scheme is designed to account for the small amount of correlation energy of the Ryberg electron and to facilitate calculation of term values from a corresponding calculation on the positive ion. With one exception the results are in agreement with the recent spectral assignments of Mulliken. Both the present results and those of other theoreticians illustrate the difficulties of calculating Rydberg states.
56 citations
TL;DR: In this paper, the potential surfaces for the 2E″ state of planar cyclopropenyl and the 1E′ state of the anion were examined using full pi-space configuration interaction within an STO-3G basis.
Abstract: The potential surfaces for the 2E″ state of planar cyclopropenyl and the 1E′ state of planar cyclopropenyl anion are examined using full pi‐space configuration interaction within an STO‐3G basis. Both states are subject to first order Jahn–Teller distortions of the bond lengths. Small second order effects slightly favor the ethylenic form of the radical. Much larger second order effects strongly favor the allylic form of the anion.
47 citations
TL;DR: In this paper, the ground and low-energy excited states of formamide were calculated at the ground state geometry and the predicted triplet energies lie at 5.4 eV (3nπ*) and 5.8 eV(3ππ*) respectively.
Abstract: Calculated energy and molecular properties of the ground and low-energy excited states of formamide are presented at the ground state geometry. Satisfactory results are obtained except for the 1ππ* energy which remains too high by 1 eV (which is nevertheless a large improvement over previous calculations). The predicted triplet energies lie at 5.4 eV (3nπ*) and 5.8 eV (3ππ*).
40 citations
TL;DR: A theoretical study of the origin of the intense satellite structure observed in the carbon (2s) derived region of the X-ray photoelectron spectrum of ethylene is reported in this article.
TL;DR: By using SCF and stabilization-like procedures, a (π, π*) singlet resonance-like state in ethylene at 10.21 eV was found in this paper, which is the analog to the spectroscopic V state in Hartree-Fock theory.
Abstract: By using SCF and stabilization‐like procedures, we have located a (π, π*) singlet resonance‐like state in ethylene at 10.21 eV. This state is embedded in the ionization continuum and carries an oscillator strength of 0.46 and is probably the analog to the spectroscopic V state in Hartree–Fock theory. Implications of these results for other systems are discussed.