Natural orbitals for H sub 2.
Natural orbital expansion coefficients of LCAO-MO-SCF-CI wave functions for ground state of H molecule
Barker, W. H.↗
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Integral Hellmann-Feynman analysis of the binding energy of H2 and LiH using atomic reference states
Integral Hellman-Feynman formula applied to binding energy of molecular H and LiH, using SCF wavefunctions for atomic states
Marron, M. T.↗
Electronic structure of CaO. I
Electronic wavefunctions for 15 states of CaO arising (nominally) from six electron occupancies are calculated at the single configuration (sc) SCF level and analyzed qualitatively in terms of Mulliken populations and an approximate overlap criterion. The accuracy of the sc approximation is assessed and shown to be highly inadequate in several cases. Approximate Te's are extracted from these results when warranted by the quality of the sc wavefunctions. An improved two configuration wavefunction for the lowest 1 Sigma + state is also determined and discussed in detail.
Bauschlicher, C. W., Jr.↗
Metal-to-metal charge transfer transitions - Interpretation of visible-region spectra of the moon and lunar materials
Prominent bands in the spectral profiles of Fe-Ti phases in lunar samples have been attributed to charge-transfer transitions between Fe and Ti cations, and a model is presented for calculating charge transfer energies from energy levels computed by the SCF-X(alpha) scattered wave molecular orbital method for isolated MO6 octahedral coordination clusters containing Fe(2+), Fe(3+), Ti(3+), and Ti(4+) cations. The calculated charge transfer energy for the Fe(2+) to Ti(4+) transition correlates well with a measured spectral feature around 0.6 micron in ilmenite, and, since ilmenite is a major constituent of mare basalts and dark-mantling material, the observed darkness and blueness of the regolith in lunar black spots is attributed primarily to this transition. The Ti(3+) to Ti(4+) transition is thought to contribute to some phases.
Loeffler, B. M.↗
Theoretical study of the photodissociation of HOCl
A study of the UV photodissociation of hypochlorous acid is conducted on the basis of ab initio SCF-Cl calculations. These calculations show that HOCl has only a single peak in the UV photoabsorption spectrum at 220 nm. This result implies that HOCl would have a long lifetime for photodissociation if it were to be formed in the stratosphere. The photodissociation products of HOCl have been identified as Cl+OH, based on an examination of the topographies of the excited electronic state potential energy surfaces. The results of this study indicate that HOCl could be a significant reservoir for stratospheric chlorine.
Jaffe, R. L.↗
Ab initio studies of the electronic structure of UF6, UF6/+/, and UF6/-/ using relativistic effective core potentials
The paper presents ab initio calculations performed on the electronic states of UF6, UF6(+), and UF6(-) using a relativistic effective core potential (ECP) for uranium and a nonrelativistic ECP for fluorine. In most of the calculations 56 valence electrons are treated explicitly using a contracted (3s 3p 2d 2f/2s2p) Gaussian basis. It is noted that various ECP's were explored, but all yield an overall charge density of U(+2.4)/F(-0.4)/6. In addition, the bonding in the ground state of UF6 is discussed. SCF and CI calculations on UF6(+) are compared with the experimental photoelectron spectrum and with previous scattered wave calculations. Further, the role of spin-orbit coupling in the states of UF6(+) and UF6(-) is covered. Finally, it is concluded that the calculated electron affinity of UF6 (7.1 eV) is considerably larger than in current experimental estimates, but the relative energies of the states of UF6(-) are in agreement (0.1-0.2 eV) with those of the experiment.
Hay, P. J.↗
An ab initio investigation of the structure, vibrational frequencies, and intensities of HO2 and HOCl
The infrared spectral intensities for HOCl and HO2 have been calculated using a new ab initio technique. Theoretical results for the geometries, vibrational frequencies, and the dipole moments of these species are also reported. All of the calculations were performed at the SCF level using near Hartree-Fock quality basis sets. The results for the molecular geometries and the vibrational frequencies are in good agreement with available experimental data. It is believed that the computed intensities are accurate to at least 50%. The results should be helpful in attempts to determine the stratospheric abundance of HOCl and HO2 by in situ infrared spectroscopic measurements.
Komornicki, A.↗
On the 3d2 4s2, 3d3 4s1, and 3d4 states of Ti
The energies of the 3F (3d2 4s2), 5F (3d3 4s1) and 5D (3d4) states of Ti are investigated on the basis of MCSCF and CI calculations. Following SCF calculations using a basis set including the primitive set of Wachters (1970) and the diffuse d function of Hay (1977), four full-electron CI calculations involving the 3d and 4s electrons were performed to obtain the natural orbitals, and the full CI calculations were repeated. MCSCF calculations then performed using the most important configurations of the natural orbital basis are found to be in agreement with those of Dunning (1980), but to differ from CI results. CI(SD) calculations including single and double excitations from the MCSCF reference are found to be in agreement with the full CI but differ from experimental energy separations. Further calculations reveal that Dunning's MCSCF description is an oversimplication of the problem, and that the 5F-5D separation at the CI(SD) level is in good agreement with experiment for all basis sets but the 3F state is too low relative to the 5F and 5D states.
Bauschlicher, C. W., Jr.↗
Quantum mechanical study of elastic scattering and rotational excitation of CO by electrons
Coupling calculations of differential, integral, and momentum transfer cross sections for pure elastic scattering and rotational excitation of CO by electron impact are reported. The calculations are based on a static charge distribution that has correct dipole and quadrupole moments, has cusps at the nuclei, and is augmented by an SCF treatment of charge polarization and a local approximation for exchange. The rotationally summed cross sections, with no adjustable parameters in the scattering calculation, are in reasonably good agreement with the experimental cross sections but are somewhat larger at small scattering angles.
Onda, K.↗
A hybrid method for improving MCSCF convergence
It has been found that the convergence problems for many ill conditioned single-configuration SCF calculations arise from mixing among only a small number of orbitals. This orbital set includes the highest closed, the partially filled, and (possibly) a few of the lowest virtual orbitals. The fact that convergence problems can be, in very large measure, linked to a small orbital set is used to design a hybrid MCSCF procedure in which these orbitals are treated using a second-order MCSCF method, while other mixings are treated with a lower-order method which avoids the time consuming integral transformation. Tests on BeO show that the hybrid method yields convergence even when the simple lower-order treatment diverges. The method is expected to facilitate determination of MCSCF wave functions for large basis problems and for the construction of potential energy surfaces.
Bauschlicher, C. W., Jr.↗
On correlation in the first row transition metal atoms
CI (SD) calculations using both SCF and MCSCF references have been performed for the first-row transition metal atoms. Basis sets as large as 84 STO's have been used. At the highest level of calculation, good agreement with experiment is found. If relativistic effects are considered, the agreement is somewhat poorer. This aspect, as well as the trends and results, is discussed.
Bauschlicher, C. W., Jr.↗
Ab initio calculation of infrared intensities for hydrogen peroxide
Results of an ab initio SCF quantum mechanical study are used to derive estimates for the infrared intensities of the fundamental vibrations of hydrogen peroxide. Atomic polar tensors (APTs) were calculated on the basis of a 4-31G basis set, and used to derive absolute intensities for the vibrational transitions. Comparison of the APTs calculated for H2O2 with those previously obtained for H2O and CH3OH, and of the absolute intensities derived from the H2O2 APTs with those derived from APTs transferred from H2O and CH3OH, reveals the sets of values to differ by no more than a factor of two, supporting the validity of the theoretical calculation. Values of the infrared intensities obtained correspond to A1 = 14.5 km/mol, A2 = 0.91 km/mol, A3 = 0.058 km/mol, A4 = 123 km/mol, A5 = 46.2 km/mol, and A6 = 101 km/mol. Charge, charge flux and overlap contributions to the dipole moment derivatives are also computed.
Rogers, J. D.↗
Spin-polarized atomic nitrogen and the 7Sigma + u state of N2
The first self-consistent field (SCF) calculation of the repulsive 7Sigma + u state of molecular nitrogen is presented. This calculation is used with attractive dispersion to provide a model potential for electron spin-polarized atomic nitrogen N appropriate in the range of 2.5-20A(O). Potential parameters obtained from the calculation are used to provide estimates of equilibrium thermodynamic properties of spin-polarized N in the quantum theorem of corresponding states framework. Consideration is given to increased stability of spin-polarized N with respect to single electron spin-flip processes, as compared to spin-polarized H.
Ferrante, R. F.↗
Theoretical study of silicon dicarbide
Silicon dicarbide was first observed in 1926 in spectra of cool carbon stars. The carrier of these bands around 5000 A was tentatively identified as SiC2 by Kleman (1956) who produced similar spectra by inserting silicon into the graphite tube of a King furnace heated to over 2500 K. This identification was strengthened by subsequent mass spectral studies which showed SiC2 as a major molecular component of vaporized silicon carbide. The present investigation is concerned with calculations which were initiated in an attempt to understand more recent astronomical observations of unidentified lines in the millimeter-wave region of the spectrum. The calculations were designed to determine the ground state equilibrium structure and to obtain vibrational and rotational constants. Calculations for estimating the positions and structure of low-lying electronic states were also performed. Self-consistent field (SCF) calculations were performed assuming a closed-shell electronic structure analogous to that in C3. Calculations were conducted for symmetric CSiC, and asymmetric SiCC forms.
Green, S.↗
On the nature of the bonding in Cu2 - An ab initio viewpoint
The bonding in Cu2 has been calculatively investigated. A CASSCF calculation is performed where the two 4s electrons are distributed in all possible ways among the 4s and 4p orbitals. The CAS results have a 3d population of 9.99. The corresponding orbitals between the CAS core orbitals at r(e) and the atomic SCF core orbitals show an overlap of 13.9992 out of a possible 14, with all of the change in sigma space. Thus, the CAS results show virtually no change in the d orbitals relative to the atom and can be considered as showing only a single bond. The reduction in 3d population, the decrease in r(e), and the increase in D(e) upon correlating the 3d shell indicates that the 3d electrons are slightly involved in the bonding, but there is no indication of the formation of a triple bond.
Bauschlicher, C. W., Jr.↗
On the low-lying states of TiN
A series of CAS SCF and multi-reference CI calculations are used to describe the lowest states of TiN. The bonding in all states is described as a triple bond involving the Ti 3d orbitals. The system has some ionic character as seen from both population analysis and dipole moment. The origins of the excited states are discussed.
Bauschlicher, C. W., Jr.↗
The nature of the metal-CO interaction and bonding
The adsorption of CO on metal surfaces is represented by molecular orbital cluster models of CO at an on top site and adsorbed normal to the surface carbon end down. Ab initio SCF and MCSCF calculations are performed for several clusters. The new constrained space orbital variation CSOV approach is used to analyze the bonding and to compare CO adsorption on Al, representative of sp metals, with that on Cu, representative of transition metals. There is a large repulsion between the superposed free CO and metal charge distributions which is considerably smaller for Cu than for Al because there are fewer valence sigma electrons for Cu than for Al. The CSOV analysis shows that the metal to CO pi donation is much more important than the CO to metal sigma donation. It is also shown that for Cu, the d pi contribution to the metal pi donation is larger than the valence 4p pi contribution. The d pi donation is compared between Fe, Ni, and Cu and this donation and the metal-CO interaction are found to be different in the order Fe greater than Ni greater than Cu.
Bagus, P. S.↗
Reassignment of the Iron (3) Absorption Bands in the Spectra of Mars
Absorption features in the near-infrared and visible region reflectance spectra of Mars have been assigned to specific Fe (3+) crystal-field and o(2-) yields Fe(3+) charge transfer transitions. Recently, near-ultraviolet absorption spectra of iron oxides were obtained and the energies of o(2-) yields Fe(3+) charge-transfer (LMCT) transitions were determined from accurate SCF-X # alpha-SW molecular orbital calculations on (FeO6)(9-) and (FeO4)(5-) clusters. Both the theoretical and experimental results, together with existing data in the literature, show that some of the previous Fe(3+) band assignments in the spectra of Mars need to be revised. The theory of Fe(3+) spectra in minerals is discussed and applied to the spectrum of Mars.
Sherman, D. M.↗