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Showing papers on "Ab initio quantum chemistry methods published in 1971"


Journal ArticleDOI
TL;DR: In this paper, the force constants of the molecules HF, NH3, CH4 and BH4 have been calculated ab initio by the force method with a 73/3 + 1 gaussian lobe basis set.
Abstract: Force constants of the molecules HF, NH3, CH4 and BH4 - have been calculated ab initio by the force method with a 73/3 + 1 gaussian lobe basis set The results, including a former calculation on H2O, agree well with experiment: the average relative error is 12 per cent for the diagonal force constants and the average absolute error is 0·06 mdyn/A for the off-diagonal ones The trends are also correctly reproduced It is concluded that ab initio calculations of this accuracy can help to solve a number of spectroscopic problems Force constants of BH4 - have been determined from a combination of spectroscopic and ab initio information Geometries have been obtained with little computing work and show good agreement with experiment

111 citations


Journal ArticleDOI
TL;DR: In this paper, the vibronic potential surface of the 2 T 2 ground state of CH4 + has been calculated using a contracted gaussian approximation to a double-zeta basis of Slater orbitals.
Abstract: Ab initio calculations of the vibronic potential surface of the 2 T 2 ground state of CH4 + have been carried out, using a contracted gaussian approximation to a double-zeta basis of Slater orbitals. The minimum energy is found for a tetragonal distortion to the point group D 2d , with two HCH angles of 141° and four of 96°, and all r ch equal. All calculations for distorted CH4 + were carried out with the mean r ch held at 1·147 a, which minimises the energy for Td symmetry. The distortion from Td symmetry lowers the electronic energy by 1·41 ev. Distortions from Td to C 3v lead to a maximum stabilization of 1·22 ev. Vibronic perturbation parameters derived from this surface are employed in discussions of the 2 T 2-1 A 1 photoelectron transition of CH4 and a possible 2 E←2 B 2 absorption transition of CH4 +. A vibrational interval of ∼ 1200 cm-1 observed near the origin of the 2 T 2-1 A 1 photoelectron transition is assigned to one component of v 2 (calculated frequency, 1300 cm-1).

103 citations


Journal ArticleDOI
TL;DR: In this article, Bernheim et al. carried out ab initio calculations at 28 C2υ geometries for the lowest 1A1, 1A2, 3A2 and 3B2 states of CH2, including all singly and doubly excited configurations and the iterative natural orbital procedure was used to obtain an optimum set of orbitals.
Abstract: Ab initio calculations have been carried out at 28 C2υ geometries for the lowest 1A1, 1A2, 3A2, 1B1, 3B1, 1B2, and 3B2 states of CH2 The basis set used was of the contracted Gaussian type with four s and two p functions on carbon and two s functions on hydrogen In all calculations except 1A1 the SCF configuration plus all singly and doubly excited configurations were included (holding the K shell frozen), and the iterative natural orbital procedure was used to obtain an optimum set of orbitals For the 1A1 state a two configuration SCF calculation was used as the starting point for the configuration interaction calculations In a preliminary communication we predicted the triplet ground state of CH2 to be bent, and this prediction has since been justified experimentally by Bernheim et al and by Wasserman et al For the 1A1 state the ab initio geometry is r = 113 A, θ = 104°, compared to experiment, r = 111 A, θ = 102° For the 1B1 state the predicted geometry is r = 109 A, θ = 144°, as opposed to ex

83 citations


Journal ArticleDOI
Ulrik Gelius1, C.J. Allan1, D.A. Allison1, Hans Siegbahn1, Kai Siegbahn1 
TL;DR: The ESCA spectrum of C3O2 excited by Mg Kα radiation, 1253.6 eV, has been obtained for both gaseous and solid samples.

77 citations


Journal ArticleDOI
TL;DR: In this paper, 11 internuclear separations ab initio calculations have been carried out on those 59 molecular states of CN which dissociate to atomic limits up to 1DC + 2DN.
Abstract: At 11 internuclear separations ab initio calculations have been carried out on those 59 molecular states of CN which dissociate to atomic limits up to 1DC + 2DN. Four electrons are held frozen in carbon and nitrogen 1s Hartree–Fock atomic orbitals, and a full configuration interaction is carried out for the remaining nine electrons using optimized 2s and 2p Slater‐type orbitals on each atom. The 2Π calculations, which include 486 configurations, are the most complicated. Eighteen significantly bound states (De ≥ 0.84 eV) were obtained, nine of which have been observed spectroscopically. With the exception of the third 2Π state, the theoretical ordering of states agrees with experiment. Three of the states never observed experimentally (4Σ+, 4Π and 4Δ) lie below all but three of the known states of CN. Calculated spectroscopic constants are compared with experiment. The potential curves show many interesting features, including potential maxima in the 4Σ−, 2Σ−, J 2Δ, and 2Π IV bound states. By performing n...

74 citations



Journal ArticleDOI
TL;DR: In this article, an ab initio procedure for investigation of large molecules is described, which involves two steps, the first of which is the determination of a set of orbitals by the examination of molecular fragments.
Abstract: An ab initio procedure for investigation of large molecules is described. The procedure involves two steps, the first of which is the determination of a set of orbitals by the examination of molecular fragments. These molecular fragments and associated orbitals are then combined to form large molecules of interest, using an ordinary LCAO MO SCF‐type procedure. The molecular fragment investigations employed are designed to obtain nonlinear parameters for use in large molecules, and are not used in this study to obtain “small molecules” from which “large molecules” can be formed. Several descriptions of molecular fragments are explored, in which floating spherical Gaussian orbitals are employed, and applications of the method to ethane, propane, ethylene, and benzene are given. Comparisons are made with other methods, and several general characteristics of the method are also discussed.

58 citations


Journal ArticleDOI
TL;DR: In this paper, two ab initio calculations with different basis sets have been performed on the molecule furan, C4H4O. The calculations were done with a new computer program, this paperLECT, which is presented.

54 citations


Journal ArticleDOI
TL;DR: In this article, the excited states of permanganate and chromate ions are described by better-than-minimal basis set SC FMO CI calculations, compared with the experimental absorption spectra.

53 citations


Journal ArticleDOI
TL;DR: In this article, an all-electron SCF-LCGO-CO computation for the ground state wave function of an infinite polyenic chain is presented, which demonstrates that ab initio calculations on the electronic structure of polymers become actually feasible.
Abstract: In this work, we report an all-electron SCF–LCGO–CO computation for the ground state wave-function of an infinite polyenic chain. This work demonstrates that ab initio calculations on the electronic structure of polymers become actually feasible. Our results are compared with previously obtained semi-empirical ones.

50 citations


Journal ArticleDOI
TL;DR: In this article, a double zeta plus −polarization and Rydberg function basis of Slater functions is used to calculate the ab initio dissociation energy of the X −B separation.
Abstract: Ab initio calculations, including electron correlation, have been carried out on the X 1Σ+, B 1Σ+, and lowest 3Σ+ states of BH. The last two states can be thought of as arising from the 1σ22σ23σ 4σ electron configuration. A double‐zeta‐plus‐polarization and Rydberg function basis of Slater functions is used and electron correlation is considered through the use of approximate ``first‐order'' wavefunctions. Optimum wavefunctions for the B 1Σ+ state are obtained by repeated diagonalization of the density matrix arising from the second eigenvalue of the 1Σ+ secular equation. For the ground state the ab initio dissociation energy is 3.27 eV, compared to Gaydon's experimental value 3.54 ± 0.04 eV. Other spectroscopic constants for the X 1Σ+ and B 1Σ+ states are also in good agreement with experiment. The X—B separation is calculated to be 51 770 cm−1, compared to the experimental value 52 347 cm−1. The B 1Σ+ calculations confirm the double minimum predicted by Browne and Greenawalt. The lowest 3Σ+ state is predicted by the present treatment to be Rydberg‐like (with a minimum at 1.173 A) for short internuclear separations and valencelike (repulsive) for large separations. A maximum occurs in the 3Σ+ potential curve at 1.45 A. Natural‐orbital analyses and electron density plots are used to describe the valence to Rydberg ``transition.''

Journal ArticleDOI
TL;DR: In this article, the first water molecule was calculated to have hydration energies of 43.6 resp. 141 kcal/mole, and at the energy minima the following metal oxygen distances were obtained: RLiO = 1.83 A and RBeO =1.56 A.

Journal ArticleDOI
TL;DR: Theoretical calculations of relative X-ray emission energies and intensities were made with all-valence-electron molecular orbital methods on the following systems: SO42-, SO32-, SCN-, ClO4-, and ClO3-. The relative energies are, for all cases, in agreement with experiments while the calculated intensities depend heavily on the approximation scheme chosen.
Abstract: Theoretical calculations of relative X-ray emission energies and intensities were made with all-valence-electron molecular orbital methods on the following systems: SO42-, SO32-, SCN-, ClO4-, and ClO3-. The relative energies are, for all cases, in agreement with experiments while the calculated intensities depend heavily on the approximation scheme chosen. The results indicate that a feature in the ClO3- spectrum previously attributed to decay products may partly originate from a molecular level. For SCN- an intensity calculation based on the ab initio calculations by McLean and Yoshimine is also presented.

Journal ArticleDOI
TL;DR: In this article, the high-resolution photoelectron spectra of XeF2, XeEF4, and XEF6 have been obtained essentially free from any impurity features, and the ionization potentials up to 28 eV have been measured.
Abstract: The high‐resolution photoelectron spectra of XeF2, XeF4, and XeF6 have been obtained essentially free from any impurity features, and the ionization potentials up to 28 eV have been measured. The results are used, in conjunction with recent ab initio calculations, to assign the molecular orbital electronic structure of these molecules. Agreement between experiment and calculation is fairly good.

Journal ArticleDOI
TL;DR: The configuration of several alkylidenephthalimidines, formed by dehydration of 3-alkyl-3-hydroxyphthalimidine, has been established by nuclear magnetic resonance techniques as discussed by the authors.
Abstract: The configuration of several alkylidenephthalimidines, formed by dehydration of 3-alkyl-3-hydroxyphthalimidines, has been established by nuclear magnetic resonance techniques. When the nitrogen substituent is alkyl or aryl the configuration is (E) but when hydrogen it is (Z). Isomerization was observed in the temperature range 60-140°.

Journal ArticleDOI
TL;DR: In this article, a theoretical investigation of the excited electronic states of the equilateral triangular H3+ ion was performed using the single center expansion configuration interaction method, and the potential energy curve in D3h symmetry was obtained.
Abstract: A theoretical investigation of the excited electronic states of the equilateral triangular H3+ ion is reported. Ab initio calculations were performed for the lowest energy states of symmetries 3A1′, 1A2″, 3A2″, 1E′, and 3E′, using the single‐center expansion configuration‐interaction method. For each state we have obtained the potential‐energy curve in D3h symmetry. The calculated state energies are expected to be in error by at most 0.01 hartree (6 kcal/mole). Two of the excited states 1E′ and 3E′ were found to be purely repulsive with respect to the totally symmetric nuclear coordinate, while three excited states 1A2″, 3A2″, and 3A1′ showed minima with respect to the totally symmetric nuclear coordinate. However, arguments based on group‐theoretical correlation between our calculated D3h state energies and the energies of possible dissociation products suggest that none of the excited states considered achieves an absolute energy minimum in D3h symmetry. For the allowed electric dipole transitions 1A2″ ...

Journal ArticleDOI
TL;DR: In this article, ground states of trans-, perpendicular-and cis-glyoxal are studied by ab initio calculations using Gaussian-type basis functions, and trans-Glyoxal is found to be the stable form of the molecule.

Journal ArticleDOI
TL;DR: Ab initio calculations on trajectories and nonadiabatic transitions in reactions of hydrogen atomic ions with hydrogen molecules were performed in this article, where the trajectories of hydrogen atoms and molecules were assumed to follow a non-stationary trajectory.


Journal ArticleDOI
TL;DR: In this paper, the standard deviations obtained are 4.1 cm−1 for Er3+ and 11 cm− 1 for Nd3+ (over four manifolds comprising 23 levels).

Journal ArticleDOI
TL;DR: In this article, zero-differential overlap calculations are compared with minimal basis set ab-initio calculations in order to assess their validity in the interpretation of experimental electron density maps.


Journal ArticleDOI
TL;DR: In this article, the authors show that near HF energies can be obtained with small GTO basis sets and optimized functions in the centers of chemical bonds, while energy differences, force constants and charge distributions remain unchanged, if the number of gaussian functions representing the cusp at the nuclei is reduced drastically.

Journal ArticleDOI
TL;DR: In this article, the simplified ab-initio method described in an earlier paper is tested on some hydrogen-containing molecules and the performance is slightly below that found previously for molecules composed entirely of first-row atoms but should be suitable for applications where limited numerical accuracy is sufficient.
Abstract: The simplified ab-initio method described in an earlier paper is tested on some hydrogen-containing molecules. The performance is slightly below that found previously for molecules composed entirely of first-row atoms but should be suitable for applications where limited numerical accuracy is sufficient. The hope of improved performance through limited expansion of the basis, especially on hydrogen, is not realised and so alternative treatments of the two-electron many-centre integrals should be sought if greater numerical accuracy is required.

Journal ArticleDOI
TL;DR: In this paper, the use of ellipsoidal gaussian type orbitals in ab initio calculations on molecular systems of small and intermediate size was demonstrated, in both non-linear and SCF MO schemes.
Abstract: The use of ellipsoidal gaussian type orbitals in ab initio calculations on molecular systems of small and intermediate size is demonstrated, in both non-linear and SCF MO schemes. The method is an extension of Frost's Floating Gaussian Orbital Method. Results for conformational properties (barriers to internal rotation in ethane and 1,3-butadiene) are better than those obtained with basis sets containing only spherical gaussians. The usefulness of very small basis sets is discussed.

Journal ArticleDOI
TL;DR: In this paper, self-consistent field calculations were performed on the ethylene and fluoroethylene molecules to compare the effects of substituting a hydrogen atom with a fluorine atom in the two molecules.
Abstract: Self-consistent-field calculations are reported on the ethylene and fluoroethylene molecules. A comparative analysis of the two molecules shows that the effects of substituting a hydrogen atom with a fluorine atom in ethylene are fairly local. Ionization potentials in the ethylene molecule are calculated. The effects of hydrogen p-functions are studied in both molecules, and these effects are found to be rather small, particularly in fluoroethylene. A number of molecular properties are reported for both molecules.

Journal ArticleDOI
TL;DR: In this paper, the photoelectron spectrum of the metastable O 2 (1 Δ g ) was analyzed and the positions and properties of the unobservable states of O + 2 were predicted.

Journal ArticleDOI
TL;DR: In this paper, a number of first order electronic properties for the hydrocarbons C2H6, C3H8, C 2H4, C6H6 and C10H8 are investigated.
Abstract: A number of first order electronic properties for the hydrocarbons C2H6, C3H8, C2H4, C6H6, and C10H8 are investigated. The wavefunctions employed here result from SCF calculations, using basis orbitals that have been optimized in molecular fragment studies. Comparisons are made with experimental values as well as with other calculated values, and the suitability of various molecular fragment bases is discussed.

Journal ArticleDOI
TL;DR: In this article, second order perturbation theory is used to calculate the eleven parameters which characterize the effective two-electron magnetic interaction in both Pr2+ and Pr3+. Good agreement is obtained with the Pr 2+ experimental parameters without introducing screening.
Abstract: For pt. I see abstr. A25410 of 1971. The usefulness of a 'model building' approach to rare earth configuration interaction is emphasized as an alternative to doing full ab initio calculations. Second order perturbation theory is used to calculate the eleven parameters which characterize the effective two-electron magnetic interaction in both Pr2+ and Pr3+. Good agreement is obtained with the Pr2+ experimental parameters without introducing screening.