Showing papers by "Ernest R. Davidson published in 1993"
TL;DR: The correlation energies for 3- to 10-electron atomic ions are recomputed using more recent experimental and theoretical data and the correlation energies obtained from some density-functional models are also compared to these correlation energy data.
Abstract: Recently Davidson [ital et] [ital al]. [Phys. Rev. A 44, 7071 (1991)] have estimated nonrelativistic correlation energies and relativistic corrections to ionization potentials for atomic ions with up to 10 electrons. In this work, this approach is extended to atomic ions with 11 to 18 electrons. The correlation energies for 3- to 10-electron atomic ions are also recomputed using more recent experimental and theoretical data. Unlike other work the method focuses on the correlation contribution to the individual ionization energies which are obtained by comparing experimental data with relativistic complete-valence-space energies. [ital Ab] [ital initio] estimates of correlation contributions to the ionization energies with extensive configuration-interaction calculations of 3- to 10-electron atomic ions with nuclear charge from 4 through 10 and 18, 36, 50, 72, 100, and 144 have been obtained. The correlation energies obtained from some density-functional models are also compared to these correlation energy data.
487 citations
107 citations
TL;DR: In this article, zero kinetic energy electron spectra of aniline were recorded and a number of ion vibrational frequencies accurately measured and the adiabatic ionization potential was found to be 62.271±2 cm−1.
Abstract: Zero kinetic energy electron spectra of aniline are recorded and a number of ion vibrational frequencies accurately measured. The adiabatic ionization potential of aniline is found to be 62 271±2 cm−1. Ab initio calculations provide insights into the bonding changes that take place in aniline upon ionization. Reasonable agreement between calculated and measured frequencies in the ground states of aniline neutral and ion is obtained.
101 citations
101 citations
TL;DR: In this article, the binding energy of the water dimer at the experimental geometry has been calculated employing the Hartree-Fock (HF) method, MOller-Plesset theories MP2, MP3, and MP4, and the coupled cluster method with double excitations.
Abstract: The binding energy of the water dimer at the experimental geometry has been calculated employing the Hartree-Fock (HF) method, MOller-Plesset theories MP2, MP3, and MP4, and the coupled cluster method with double excitations. We have also used configuration interaction wavefunctions both at the HFSDCI (single and double excitations from the HF configuration) and MRSDCI (single and double excitations from multiple reference configurations) levels to calculate the interaction energy. Binding energies within quasi-degenerate variation perturbation theory, linearized coupled cluster method, and the average pair correction model are also calculated. The basis set developed and employed in the study yields -76.0674 au for the HF energy of the water monomer at the experimental geometry
82 citations
TL;DR: In this article, a fixed basis set and geometry and many model wavefunctions were used to examine hydrogen bonding in the HF dimer, and the best result at the optimized MP2 geometry recovered only 30% of the empirical estimate of the correlation contribution to the binding energy.
Abstract: Hydrogen bonding in the HF dimer is examined using a fixed basis set and geometry and many model wavefunctions. All of the correlated methods based on the Hartree-Fock reference function give essentially the same binding energy. These include MP2, MP4, LCC, CCSD(T), and SDCI (relative to the supermolecule). Multireference methods give an improved absolute energy but a worse binding energy. The basis set superposition error for the basis set developed here was negligible in the Hartree-Fock energy but was still significant in the correlation energy even though 85% of the total correlation energy was recovered. The best result at the optimized MP2 geometry recovered only about 30% of the empirical estimate of the correlation contribution to the binding energy
53 citations
35 citations
TL;DR: The binding energy of Cr(CO) 6 was investigated using correlated methods in this article, which yielded intimates of the binding energy which were about 72% and 90% of the experimental value.
Abstract: The binding energy of Cr(CO) 6 was investigated using correlated methods. The multireference CI and QDVARPT approaches yield intimates of the binding energy which are about 72% and 90% of the experimental value. The radial correlation between electrons in the 5σe g , 3d * e g , 3dt 2g , and 2π * t 2g , orbitals is the predominant source of the correlation correction to the bonding
24 citations
TL;DR: In this paper, the S 1 ( 1 B 2u )-S 0 ( 1 A g ) spectroscopy of p-difluorobenzene-d 4 (C 6 D 4 F 2, pDFB-d4 ) cooled in a supersonic free jet expansion has been characterized by fluorescence excitation (FE) and dispersed fluorescence.
Abstract: The S 1 ( 1 B 2u )-S 0 ( 1 A g ) spectroscopy of p-difluorobenzene-d 4 (C 6 D 4 F 2 , pDFB-d 4 ) cooled in a supersonic free jet expansion has been characterized by fluorescence excitation (FE) and dispersed fluorescence. The O 0 0 band lies at 36 987±1.0 cm -1 (vacuum). The FE band assignments have provided the values of 11 S 1 fundamentals. The pattern of Franck-Condon allowed vibrational activity and of vibronically induced transitions is similar to that of pDFB-h 4
22 citations
15 Apr 1993
TL;DR: In this article, the valence orbital momentum profiles of hydrogen fluoride have been obtained using electron momentum spectroscopy at an impact energy of 1200 eV. The present results show significant differences from earlier measurements.
Abstract: The valence orbital momentum profiles of hydrogen fluoride have been obtained using electron momentum spectroscopy at an impact energy of 1200 eV. The present results show significant differences from earlier measurements. (J. Electron Spectry. Relat. Phenom. 21 (1980) 71) for the (3σ) −1 ionization but are in good agreement for the (1π) −1 processes. The measurements are compared with calculations ranging from minimum basis set to highly saturated basis sets essentially at the Hartree-Fock limit and also with numerical Hartree-Fock calculations. The experimental momentum resolution is incorporated into the calculations using the recently developed GW-PG resolution folding method (Chem. Phys. 159 (1992) 347). The significant discrepancy remaining between SCF limit calculations and experiment indicates the importance of electron correlation and relaxation effects in describing the momentum profile corresponding to the removal of the 1π electron. These effects are investigated using multireference singles and doubles CI calculations of the full ion-neutral overlap distribution and considerable improvement in the agreement between theory and experiment is then achieved.
19 citations
TL;DR: The outermost valence electron momentum profiles have been obtained at high-momentum resolution for acetone (5b 2 ) and acetaldehyde (10a′) as discussed by the authors, compared with calculated profiles of wide ranging quality from minimal basis STO-3G to near Hartree-Fock limit SCF treatments, together with the outermost momentum profile of formaldehyde (2b 2 ), measured previously by Bawagan et al.
TL;DR: In this paper, an interpretation of the first-order wave function is presented in terms of correlation factors in the two-body distribution function, and an argument is given for using N(N-1)/2 instead of N/2 as the number of pairs in approximate corrections to SDCI.
Abstract: An interpretation of the first-order wave function is presented in terms of correlation factors in the two-body distribution function. An argument is given for using N(N-1)/2 instead of N/2 as the number of pairs in approximate corrections to Single and Double Configuration Interaction (SDCI).
TL;DR: In this article, a constrained least-squares method was used to determine parameters for use in an atomic multipole description of the electrostatic energy, and the results showed that at closer distances, penetration of the charge distributions invalidates the multipole expansion.
Abstract: In this study, we used a constrained least-squares method to determine parameters for use in an atomic multipole description of the electrostatic energy. To test the accuracy of the parameters, we compared acetamide dimer binding energies determined from the multipole scheme with those from a Morokuma analysis. Interestingly, it was found that a model employing only atomic point charges was able to accurately reproduce the ab initio electrostatic energies at the van der Waals separation of the dimer. The least-squares charges were closer to Mulliken charges than to other definitions which have been suggested. At closer distances, penetration of the charge distributions invalidates the multipole expansion.
TL;DR: In this paper, the effect of the alkali metal on the vertical electronic transitions is studied and compared with the transitions calculated for the free X 2 - molecules, which support the ultraviolet spectral assignment of the absorption bands near 300 nm for M + F 2 - and 340 nm for m + Cl 2 - to be the σ → σ * transition.
Abstract: This paper reports the transition energies of the low-lying valence states of some alkali-metal dihalide (MX 2 ) systems using the multireference single- and double-excitation configuration interaction method. The effect of the alkali metal on the vertical electronic transitions is studied and compared with the transitions calculated for the free X 2 - molecules. The results support the ultraviolet spectral assignment of the absorption bands near 300 nm for M + F 2 - and 340 nm for M + Cl 2 - to be the σ → σ * transition
TL;DR: In this paper, zero kinetic energy electron spectra of aniline were recorded and a number of ion vibrational frequencies accurately measured and the adiabatic ionization potential was found to be 62.271±2 cm−1.
Abstract: Zero kinetic energy electron spectra of aniline are recorded and a number of ion vibrational frequencies accurately measured. The adiabatic ionization potential of aniline is found to be 62 271±2 cm−1. Ab initio calculations provide insights into the bonding changes that take place in aniline upon ionization. Reasonable agreement between calculated and measured frequencies in the ground states of aniline neutral and ion is obtained.
IBM1
TL;DR: In this article, the ΔSCF method was used to capture electron correlation effects and the calculated C 1s and O 1s ionization energies including electron correlation were within ∼0.5 eV of the experimental values.
Abstract: The C 1s and O 1s ionization energies are calculated for formaldehyde, acetaldehyde, and acetone, and the calculated results are compared to the experimental X-ray photoelectron spectra. The theoretical techniques employed involve the ΔSCF method followed by a perturbative CI treatment to capture electron correlation effects. The calculated C 1s and O 1s ionization energies including electron correlation are within ∼0.5 eV of the experimental values
TL;DR: In this paper, the effect of the alkali metal on the vertical electronic transitions is studied and compared with the transitions calculated for the free X 2 - molecules, which support the ultraviolet spectral assignment of the absorption bands near 300 nm for M + F 2 - and 340 nm for m + Cl 2 - to be the σ → σ * transition.
Abstract: This paper reports the transition energies of the low-lying valence states of some alkali-metal dihalide (MX 2 ) systems using the multireference single- and double-excitation configuration interaction method. The effect of the alkali metal on the vertical electronic transitions is studied and compared with the transitions calculated for the free X 2 - molecules. The results support the ultraviolet spectral assignment of the absorption bands near 300 nm for M + F 2 - and 340 nm for M + Cl 2 - to be the σ → σ * transition