Showing papers by "Ernest R. Davidson published in 1980"
TL;DR: This work shows that the recently developed extended Koopmans' procedures are in principle exact for the first ionization energy.
Abstract: The asymptotic form of bound-state wave functions is derived by analytic continuation of asymptotic scattering-state wave functions. The result is also regorously derived by using an approach that is independent of scattering theory. One aspect of the result is that the N electron wave function becomes the lowest accessible exact wave function for the remaining N — 1 electrons when one electron is far away from all the nuclei. This shows that the recently developed extended Koopmans' procedures are in principle exact for the first ionization energy.
246 citations
156 citations
TL;DR: In this article, Hartree-Fock theory is applied to resonance states of an atomic Hamiltonian under the complex coordinate transformation, and the resonance energy obtained in these calculations is practically independent of the phase of the complex scaling parameter for a wide range of values.
Abstract: Hartree–Fock theory is applied to resonance states of an atomic Hamiltonian under the complex coordinate transformation. It is concluded that for shape resonances restricted Hartree–Fock theory provides a useful and practical approach to the problem of computing the complex resonance energy. Numerical results are presented for the low‐energy 2P shape resonance in e–Be scattering. With properly chosen basis functions the resonance energy obtained in these calculations is practically independent of the phase of the complex scaling parameter for a wide range of values. Application of this technique to molecular resonances is discussed. The widths of Feshbach resonances cannot be obtained from the theory in its present form, but it is suggested that a complex coordinate form of multiconfiguration self‐consistent field theory may be appropriate for that case.
80 citations
53 citations
TL;DR: In this paper, it was shown that along the sequence C(NH 2 ) 2, C(OH) 2, CF 2, and F 2 2, the singlet-triplet gap decreases, due to decreased π bonding, as the substituent electronegativity increases.
51 citations
TL;DR: The mass-velocity, Darwin, and magnetic corrections to the 3 P-5 S and s 2 p 2 -sp 3 splitting of carbon and the 3 B 1 -1 A 1 splitting in CH 2 have been evaluated by first-order perturbation theory.
48 citations
31 citations
TL;DR: The transition states for fragmentation of dihydroxy carbene [C(OH)2] to H2 and CO2 and for the rearrangement of this carbene to formic acid were located by ab initio calculations as discussed by the authors.
Abstract: The transition states for fragmentation of dihydroxycarbene [C(OH)2] to H2 and CO2 and for the rearrangement of this carbene to formic acid were located by ab initio calculations. The relative energies of the transition states were determined at several levels of theory and the basis set dependence of the energies is discussed. At the best level of theory; using a basis set of double-zeta quality augmented by polarization functions and with the inclusion of extensive CI, we found that the transition state for fragmentation was considerably higher in energy than that for rearrangement. This finding is at variance with the predictions of the Woodward--Hoffmann rules because fragmentation represents an “allowed” reaction, whereas rearrangement is “forbidden.” In conformity with the Woodward–Hoffman rules, the transition state for rearrangement was found to be close in energy to H· + ·CO2H. The even higher energy of the transition state for concerted fragmentation to H2 and CO2 is attributed to the need for the latter fragment to remain substantially bent in order to permit H2 formation while maintaining a modicum of OH bonding. Difficulties in locating the transition state for concerted fragmentation are discussed and a new method for finding transition states is proposed.
29 citations
TL;DR: In this paper, a correct outline of the Davidson algorithm (1975) is given, and conceptual errors in Kalamboukis' recent paper (1980) are pointed out.
Abstract: Conceptual errors in Kalamboukis' recent paper (1980) are pointed out. A correct outline of the Davidson algorithm (1975) is given.
25 citations
24 citations
TL;DR: The 13 electron BeF radical has been generated and trapped in argon and krypton matrices at 12 K and studied via ESR spectroscopy as discussed by the authors, and the calculated dipole moment for BeF is 1.1 D.
Abstract: The 13 electron BeF radical has been generated and trapped in argon and krypton matrices at 12 K and studied via ESR spectroscopy. Comparisons are made between BeF and other similar radicals. The calculated dipole moment for BeF is 1.1 D. The magnetic parameters in argon are g∥=2.001, g⊥=2.001, Aiso(Be)=294(2) MHz, and Aiso(19F) =230(2) MHz. The 19F hfs is unusually isotropic for an MF radical, suggesting that rotational averaging might be occurring. Results of ab initio theoretical calculations are compared to the observed A tensors. The BeF molecule was generated by the codeposition of thermally produced Be atoms and molecular fluorine in the rare gas matrices.
TL;DR: In this article, the spin dipole-dipole and spin-orbit contributions to zero-field splitting of the 3A″ state of formaldehyde have been evaluated at the excited state experimental geometry.
Abstract: The spin dipole–dipole and spin–orbit contributions to the zero‐field splitting of the 3A″ state of formaldehyde have been evaluated at the excited state experimental geometry. Ab initio CI wave functions were generated from a Dunning double zeta plus polarization basis set using 3A″ rhf orbitals. Twelve states of each symmetry were used to evaluate the second‐order spin–orbit effect. The resulting values of D and E were 0.19 and 0.03 cm−1 with the principal magnetic axes rotated 36° from the CO bond. The values of α and β relative to the inertial axes were calculated to be 0.03 and 0.01 cm−1 compared to the experimental values of 0.05±0.01 and 0.02±0.02 cm−1.
TL;DR: In this paper, a cyclic carbene isomer with RCO=2.46 bohr and &OCO=79° is predicted using both 3•21G and DZP basis sets.
Abstract: The existence of cyclic isomers of O3 and NO2 has motivated a search for a cyclic isomer of CO2 on the energy surface corresponding to the electronic ground state. MCSCF and CI results were obtained using both 3‐21G and DZP basis sets. A cyclic carbene isomer with RCO=2.46 bohr and &OCO=79° is predicted.
TL;DR: In this paper, an estimated adiabatic electron affinity of 0.9 eV and 0.7 eV for glyoxal and methyl glyoxalin, respectively.
Abstract: ab initio calculations gives an estimated adiabatic electron affinity of 0.9 eV for glyoxal and 0.7 eV for methyl glyoxal. (AIP)
TL;DR: The work of Desclaux et al. as mentioned in this paper indicates that the Fock-Dirac relativistic correction to the s2p3-sp3 energy separation in carbon is of the same order of magnitude as the difference between experimental and theoretical estimates of the singlet-triplet separation in CH2.
TL;DR: In this paper, a partitioning of the kinetic and potential energies of atoms within the SCF framework into shell components is proposed, which nearly satisfies a shellwise viral theorem for SCF wave functions.
Abstract: A partitioning of the kinetic and potential energies of atoms within the SCF framework into shell components is proposed. It is demonstrated that this partitioning nearly satisfies a shellwise viral theorem for SCF wave functions. This property is used in order to generate approximate relaxed wave functions for atomic hole states by scaling each shell of the frozen description of the hole in terms of the neutral-atom ground-state orbitals. Very good estimates of ΔSCF relaxation energies and reasonable estimates of the overlap integrals between the frozen and relaxed hole wave functions are obtained.
TL;DR: In this paper, an estimated adiabatic electron affinity of 0.9 eV and 0.7 eV for glyoxal and methyl glyoxalin, respectively.
Abstract: ab initio calculations gives an estimated adiabatic electron affinity of 0.9 eV for glyoxal and 0.7 eV for methyl glyoxal. (AIP)
TL;DR: In this article, the potential surfaces for rotation of the OH groups in C(OH)2 for both the lowest singlet and triplet states were computed, and it was shown that pi electron donation is responsible for making dihydroxycarbene a ground state singlet.
Abstract: Potential surfaces have been computed for rotation of the OH groups in C(OH)2 for both the lowest singlet and triplet state. The minima on the singlet surface occur at planar geometries, which represent maxima on the triplet surface. This result is interpreted in terms of different modes of pi electron donation from oxygen being favored in the two states. Evidence is presented that shows pi electron donation is chiefly responsible for making dihydroxycarbene a ground state singlet.