Showing papers by "Ernest R. Davidson published in 1994"
TL;DR: Several possible definitions for a multireference second-order perturbation theory are suggested in this paper, and these are tested against some standard test problems from the literature, and the results show that they are testable.
Abstract: Several possible definitions for a multireference second‐order perturbation theory are suggested. These are tested against some standard test problems from the literature.
180 citations
TL;DR: In this article, a new definition is suggested for basis set superposition error and other sources of basis set incompleteness error in the interaction energy are considered Comparison is made with the counterpoise correction.
115 citations
TL;DR: In this paper, a modified form of Moller-Plesset perturbation theory for systems like cyano radical or He+2, He2+2 and O2 + 2 cations is considered.
62 citations
TL;DR: In this paper, a spin-restricted perturbation theory is proposed, which is invariant with respect to orbital degeneracy and is based entirely on the spin restricted formalism.
49 citations
TL;DR: In this paper, the binding energy spectra and momentum distributions of all valence orbitals of acetone have been studied by electron momentum spectroscopy (EMS) and SCF, MRSD-CI, and density functional theory (DFT) calculations.
47 citations
TL;DR: In this article, a series of cationic magnesium radicals (Mg+N, N=1-6) was studied by electron spin resonance (ESR) spectroscopy.
Abstract: A series of cationic magnesium radicals (Mg+N, N=1–6) was studied by electron spin resonance (ESR) spectroscopy. The ESR data indicate that all Mg nuclei are equivalent on the ESR time scale in each of these clusters. The nuclear hyperfine interactions obtained for 25Mg+N (N=1–3) in neon and argon matrices from ESR measurements were compared with ab initio calculations. The minimum energy structures for Mg+2 and Mg+3 and the transition‐state structure for Mg+3 were optimized using complete active space self‐consistent field (CASSCF) wave functions. The minimum energy structure for Mg+3 was determined to be linear and the barrier for the pseudorotation between equivalent minima was calculated. Good agreement between theory and experiment is obtained if averaging between the center and end position of Mg+3 is assumed to occur in the ESR experiment in spite of the 6 kcal/mol calculated energy barrier.
25 citations
TL;DR: In this paper, the ZEKE spectra of propylaniline were recorded by exciting 13 vibronic levels in the S1 electronic state, and a number of ring modes as well as several low-frequency torsional and bending chain modes have been identified.
Abstract: ZEKE spectra of propylaniline were recorded by exciting 13 vibronic levels in the S1 electronic state. All ZEKE spectra show well resolved vibrational structure of the anti and gauche cations. Adiabatic ionization potentials of the anti and gauche conformations were determined to be 59 717±3 cm−1 (7.4040 eV) and 59 793±3 cm−1 (7.4134 eV), respectively. A number of ring modes as well as several low‐frequency torsional and bending chain modes have been identified. Spectra demonstrate that low‐frequency chain modes are sensitive to the molecular conformation. Ab initio calculations were performed to understand the nature of these low‐frequency chain modes. S1←S0 vibronic transitions involving anti and gauche conformations can easily be distinguished using the ZEKE method.
20 citations
TL;DR: In this paper, a new correlation (satellite) peak is found at 21.4 eV binding energy, and a preliminary multi-reference singles and doubles configuration interaction (MRSDCI) calcualtion, based on average natural orbitals (ANO), is reported to provide a tentative assignment for this new peak.
10 citations
01 Jan 1994
TL;DR: The Hartree-Fock wave function for a molecule describes each orbital in the self-consistent average field of all the orbitals as mentioned in this paper, which is the best single Slater determinant and forms a useful starting point for developing an accurate wave function.
Abstract: The Hartree-Fock (HF) wave function for a molecule describes each orbital in the self-consistent average field of all the orbitals. This is the best single Slater determinant and forms a useful starting point for developing an accurate wave function. An improved wave function and energy can be obtained by expanding in a series of Slater determinants. Such an expansion is referred to as a configuration interaction (CI) wave function (Shavitt, 1977).
5 citations
2 citations