Showing papers on "Ab initio quantum chemistry methods published in 1981"
TL;DR: In this article, the quadratic and most important cubic force constants of benzene have been determined from ab initio Hartree-Fock calculations with a double-zeta basis set.
Abstract: The quadratic and the most important cubic force constants of benzene have been determined from ab initio Hartree–Fock calculations with a double‐zeta basis set. Some constants have also been recalculated using other basis sets, including a polarized one. A few empirical scale factors, applied to the ab initio force field, allow the reproduction of a large number of observed vibrational frequencies, isotope shifts, and Coriolis constants within the uncertainties of experiment and the harmonic model. It is shown that the simultaneous utilization of ab initio and spectroscopical information is sufficient for the conclusive resolution of the uncertainties and alternatives in previous empirical force fields. The resulting scale factors can be used directly to obtain force fields for other aromatic hydrocarbons from ab initio calculations. Reproduction of the observed infrared intensities is only moderately successful, even with the polarized basis set. The calculated vibronic coupling constants show qualitative agreement but important deviations from previous simpler calculations. The predicted vibrational patterns confirm Lindholm’s assignment of the photoelectron spectrum of benzene.
412 citations
TL;DR: In this article, a two-valued analytical potential function has been constructed to fit these ab initio energy calculations, and the adiabatic energies are given in their analytical function as the eigenvalues of a 2 × 2 matrix, whose diagonal elements define two diabatic surfaces.
Abstract: Ab initio calculations of the energy have been made at approximately 150 points on the two lowest singlet A′ potential energy surfaces of the water molecule, [Xtilde] 1 A′ and [Btilde] 1 A′, covering structures having D ∞h , C ∞v , C 2v and C s symmetries. The object was to obtain an ab initio surface of uniform accuracy over the whole three-dimensional coordinate space. Molecular orbitals were constructed from a double zeta plus Rydberg basis, and correlation was introduced by single and double excitations from multiconfiguration states which gave the correct dissociation behaviour. A two-valued analytical potential function has been constructed to fit these ab initio energy calculations. The adiabatic energies are given in our analytical function as the eigenvalues of a 2 × 2 matrix, whose diagonal elements define two diabatic surfaces. The off-diagonal element goes to zero for those configurations corresponding to surface intersections, so that our adiabatic surface exhibits the correct Σ/II conical in...
107 citations
TL;DR: In this paper, the puckering potential of azetidine is explored over the range −40° < o (puckering angle) < 40°, for both sp3 and sp2 hybridization of the nitrogen atom.
66 citations
TL;DR: In this paper, Ab initio electronic structure calculations have been used to characterize the equilibrium and saddle points for the addition of O(/sup 3/P) to HCCH on the two lowest triplet surfaces.
Abstract: Ab initio electronic structure calculations have been used to characterize the equilibrium and saddle points for the addition of O(/sup 3/P) to HCCH on the two lowest triplet surfaces. Structures, frequencies, and energetics are presented and, when possible, directly compared to those from experiment. The saddle point for abstraction of H from HCCH by O(/sup 3/P) has also been characterized for the two lowest triplet surfaces by analogy with recent ab initio calculations on similar abstraction reactions. Systematic errors in the calculated energetics are corrected by semiempirical arguments. Comparisons of the energetics are also made to semiempirical BAC-MP4 calculations. The final characterizations of the stationary points on the addition and abstraction surfaces are then used in RRKM calculations of the rate constants and product branching ratios. These calculations are compared to experiment. The comparisons show (1) abstraction is not an important process, (2) theory and experiment are in good agreement for the overall rate of reaction at temperatures below 1000 K but predict substantially lower rates than observed in high-temperature shock tube experiments, (3) the calculated branching ratio, production of H + HCCO over the total rate of reaction, is not small (certainly over 25% and most likely over 50%)more » with a relatively weak temperature dependence and no pressure dependence, and (4) the ground-state triplet surface (/sup 3/A') dominates both the overall rate constant and the branching ratio with the excited triplet surface (/sup 3/A') introducing only minor perturbations.« less
59 citations
TL;DR: In this article, the geometries of three conformations of FCH 2 OH and four conformations each of NH 2 CH 2 NH 2 were completely refined by ab initio calculations on the 4-21G level.
Abstract: The geometries of three conformations of FCH 2 OH and four conformations each of NH 2 CH 2 NH 2 and NH 2 CH 2 OH are completely refined by ab initio calculations on the 4–21G level. It is found that most characteristic structural and conformational properties of such systems can be reliably predicted on the basis of a simple anomeric orbital interaction model. The extension of this model to all compounds in which two electronegative substituents with non-bonding lone pairs or bonding π-electrons are attached to the same tetrahedral carbon atom, including polymer systems such as proteins, seems to be useful.
53 citations
TL;DR: In this article, multiconfiguration self-consistent field calculations have been carried out on the X 1S+ and a 3S+ states of LiH, NaH, KH, RbH, and CsH.
Abstract: Multiconfiguration self‐consistent‐field calculations have been carried out on the X 1S+ and a 3S+ states of LiH, NaH, KH, RbH, and CsH, and on the X 2S+ states of their respective anions. Pseudopotentials, including core polarization terms, have been used to replace the core electrons, resulting in simple two‐ and three‐electron calculations. Comparisons of the neutral potential curves with experiment and other ab initio calculations (where available) show very good agreement. The agreement with ab initio calculations on LiH− and NaH− is also very good. Adiabatic electron affinities have been calculated for LiH (0.293 ev), NaH (0.316 eV), KH (0.437 eV), RbH (0.422 eV), and CsH (0.438 eV).
50 citations
46 citations
TL;DR: In this article, the absolute radiative transition probabilities for previously observed spontaneous emission from A1Σu+ (v′,J′) → X 1Σg+(v″, J″ = J′ ± 1) reported in the preceding paper and by Woerdman (Chem. Phys. Lett.
46 citations
TL;DR: In this paper, the authors presented the results of calculations of the OH-H2 interaction potential for a total of seven independent geometries and the two symmetries arising from the ground electronic states of the reactants.
43 citations
TL;DR: For a series of ten electron molecules (HF, H2O, NH3, CH4) the molecular polarizability tensor and the derivatives with respect to the symmetry coordinates have been calculated from ab initio SCF wavefunctions using the finite field method as well as perturbation theory approaches as discussed by the authors.
Abstract: For a series of ten electron molecules (HF, H2O, NH3, CH4) the molecular polarizability tensor and the derivatives with respect to the symmetry coordinates have been calculated from ab initio SCF wavefunctions using the finite field method as well as perturbation theory approaches. Raman intensities and degrees of depolarization derived from the finite field results agree well with the available experimental data. The zeroth order bond polarizability model and the atom dipole interaction model have been analysed. Both models can be used to describe the computed static polarizabilities and the derivatives with respect to bond stretching, but fail for the derivatives with respect to the bending coordinates.
42 citations
TL;DR: In this article, the high pressure limiting rate constants of H and D-atom additions to C2H4 and C2D2 have been measured in the temperature range from 206 to 461 K by means of the pulse radiolysis-resonance absorption method.
Abstract: The high pressure limiting rate constants of H and D-atom additions to C2H4, C2H3D, C2D4, C2H2, and C2D2 have been measured in the temperature range from 206 to 461 K by means of the pulse radiolysis-resonance absorption method. Practically no isotope effects due to the deuteration of ethylene and acetylene could be observed. The rate constants were compared with those calculated by the activated complex theory using the potential energy surfaces provided by the ab initio calculations. Concerning the isotope effects, very poor agreement was obtained between theory and experiment. This seems to suggest that the assumptions on which the activated complex theory is based have to be reconsidered when it is applied to such reactions as H+C2H4→C2H5 and H+C2H2→C2H3.
TL;DR: In this article, the structure and stability of small clusters (with 8, 9 and 13 particles) were investigated by minimizing the total energy which comprised two-body and three-body interactions.
TL;DR: In this article, the authors employed both minimal (STO-4G) and split valence (4-31G) basis sets to study the conformational energy surface of N−benzylideneaniline (NBA).
Abstract: Ab initio calculations employing both minimal (STO–4G) and split valence (4–31G) basis sets have been used to study the conformational energy surface of N‐benzylideneaniline (NBA). The former indicate that the minimum energy conformation of NBA corresponds to a rotation about the N–phenyl bond of ≊ 45° and a rotation about the CH–phenyl bond of 0°. These results are in close correspondence with those from spectroscopic and x‐ray diffraction studies. This represents a significant improvement over the results obtained from most semiempirical methods which in general have not been able to account for the rotation about the exocyclic bonds. The compounds N‐ethylideneaniline and N‐methylbenzylidenimine were also studied and found to be good models for determining the energetics about the two exocyclic single bonds using both the minimal and extended (4‐31G) basis sets. A partitioning of the results for these two model compounds yields information which permits an analysis of the origin of the barrier to a plan...
TL;DR: The reliability of different variants of the electron gas density functional method for calculating the interaction energy of two closed-shell systems is examined by comparing the short range potentials predicted by electron gas theory with values which are exact within the assumption that the electron densities of the interacting atoms remain undistorted.
Abstract: The reliability of different variants of the electron gas density functional method for calculating the interaction energy of two closed-shell systems is examined. This is achieved by comparing the short range potentials predicted by electron gas theory with values which are exact within the assumption that the electron densities of the interacting atoms remain undistorted. It is concluded that, for systems which are adequately described by electron gas theory, the variant of Lloyd and Pugh [1] will be most reliable. It is shown that electron gas theory may fail for systems in which one or more of the occupied valence orbitals on one of the atoms has a symmetry with respect to the molecular environment which is different from that of any occupied valence orbital belonging to the other atom.
TL;DR: In this article, the properties of crystals of benzene and nonpolar azabenzenes have been calculated using a model which includes atom-atom and electrostatic intermolecular interactions.
Abstract: Statical and dynamical properties of crystals of benzene and nonpolar azabenzenes have been calculated using a model which includes atom–atom and electrostatic intermolecular interactions The molecular charge distributions are represented by placing dipoles near the nitrogen atoms and on the C–H bonds; this model reproduces very well the electrical multipoles obtained from ab initio calculations for this series of molecules The results are in good agreement with experiment, and it is observed that the higher order electrostatic interactions are fundamental for the description of the statics and dynamics of these crystals The transferability of the intermolecular potential is checked successfully by calculating the properties of crystalline pyrimidine, a polar molecule, not included in the fit
TL;DR: In this article, the effect of the inner shell orbitais, l s electrons of N atoms, is not negligibly small, while the contribution of the through-space interaction is caused from indirect as well as direct interactions between two lone pairs.
TL;DR: In this paper, a safe and simple method of preparing K[HF2] in high yield is given, in which a central fluorine acts as the acceptor to one to four HF molecules.
Abstract: Ab initio LCAO-MO-SCF calculations have been performed on the polyfluoride ions HnFn+1–, n= 1–4, and the hydrogen fluoride polymers (HF)m, m= 1–4, to determine their molecular configurations and the hydrogen-bond energies of the polyfluorides. All the polyfluorides are strongly hydrogen bonded and have structures in which a central fluorine acts as the acceptor to one to four HF molecules. The hydrogen fluoride polymers prefer open-chain arrangements. A safe and simple method of preparing K[HF2] in high yield is given.
TL;DR: In this paper, double zeta quality of conjugated 5-and 6-membered ring heterocycles containing NH and NMe groups has been investigated using microwave spectroscopy and nuclear quadrupole resonance.
Abstract: Ab initio calculations of double zeta quality have been reported for the conjugated 5- and 6- membered ring heterocycles containing NH and NMe groups. The electric field gradients were calculated and the derived nuclear quadrupole coupling constants (NQCC) compared, both in magnitude and direction, with those obtained by microwave spectroscopy and by nuclear quadrupole resonance. A comparison of the results with those of the corresponding O- and S-heterocycles, and with acyclic compounds has been given, and it was shown that aromaticity considerations were of no relevance to the NQCC values at pyridine-like N; planarity of the N atom at N-1 in the systems 2 c-9 c is responsible for the very low magnitude of Xπ, and this is clearly associated with the level of π-donation from N-1; this is a function of position of the other ring N atoms, and appears to become saturated as the ring positions become predominantly N. In particular three contiguous N atoms seem to have less effect than two N atoms
TL;DR: In this article, single average values are proposed for single-pair polarization functions on basis sets 6-31G for C-H: N-H and O-H, C-C; C-N, C -O, N-O, O-O bonds; and all lone pairs on C, N and O. Test calculations favour this type of polarization function with respect to traditional d functions.
TL;DR: In this article, the reaction energy ΔE for BH3+NH3→BH3NH3 was investigated by means of large scale ab initio calculations using extended basis sets and highly correlated wave functions.
Abstract: The reaction energy ΔE for BH3+NH3→BH3NH3 is investigated by means of large scale ab initio calculations using extended basis sets and highly correlated wave functions. The results for ΔE as obtained in the usual way or by the counterpoise method reveal serious basis saturation problems if an accuracy of 1 kcal/mol is desired for ΔE.
TL;DR: In this article, the authors presented an ab initio calculation for H 2 and D 2 relative Raman intensities originating from common rotational levels for both vibrational-rotational and pure rotational transitions.
TL;DR: In this article, the semi-empirical HAM/3 molecular orbital program has been extended to the calculation of Auger electron energies and intensities, and the results are encouraging.
TL;DR: In this article, it was shown that both H 2 BO and H 2 CN have a 2 B 2 ground electronic state and a 2 A' first excited state and that these radicals are planar and Y-shaped m the 2B 2 state but become non-planar on electronic excitation.
TL;DR: In this article, microwave observations of the J = 0-1 transitions of N2H+, 15N2H+ and 15N14ND+ have been used to determine a substitution structure for N 2H+.
Abstract: Microwave observations of the J = 0–1 transitions of N2H+, 15N2H+,and 15N14ND+, N2D+, 15N2D+, and 15N14NH+ have been used to determine a substitution structure for N2H+. The resultant structural parameters are rs(NN) = 1.0947(4) A and rs(NH) = 1.0320(1) A, which agree beautifully with those from available ab initio calculations. The frequencies obtained for the 15N species provide a basis for their future radioastronomical detection and identification.
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01 Jan 1981
TL;DR: Intermolecular forces: What can be learned from Ab Initio Calculations? as discussed by the authors Theoretical study of the Intermolecular HCL potential has been conducted using NMR methods.
Abstract: Intermolecular Forces: What Can Be Learned from Ab Initio Calculations?.- Quantum Mechanical Determination of Intermolecular Interactions. Ab Initio Studies.- Complexes of Neutral Molecules onto Negative Ions.- A Comparison of the Ab Initio Supermolecule and Interaction Approaches: Multipole Moments, Hydrogen Bonding and Ion Pairs.- The Extraction of Intermolecular Potentials from Molecular Scattering Data: Direct Inversion Methods.- Selective Vibrational Inelasticity in Proton-Molecule Collisions.- Accurate Molecular Properties, Their Additivity, and Their Use in Constructing Intermolecular Potentials.- Correlated States in Polyenes and Ion-Radical Organic Solids.- Theoretical Study of the Intermolecular HCL Potential.- "New" Molecular Bound and Resonance States.- Comparison Between Accurate Ab Initio and Electron Gas Potential Energy Surfaces.- Solute-Solute Interactions in Dilute Solutions of Gases in Liquids.- Studies of Intermolecular Forces by Vibrational Spectroscopy.- Intermolecular Forces and Spectra in Weak Charge Transfer Interactions.- Structure Determination of Collision Complexes by NMR Methods.- Electrostatic and Topological Interactions in DNA.- 1H NMR Study of the Nature of Bonding Interactions Involved in Complexes Between Nucleic Acids and Intercalating Compounds.- DNA Mono and Bisintercalators as Models for the Study of Protein Nucleic Acid Interactions: Origin of the High Affinity and Selectivity.- Empirical Models of Hydration of Small Peptides.- Stacking Interactions in Oligopeptide-Nucleic Acid Complexes.- Interaction Models for Water in Relation to Protein Hydration.- Investigations on the Role of Electrostatic Intermolecular Forces in Liquids. Ground State Properties of Amides in Solution.- On the Role of the Signal Peptide in the Initiation of Protein Exportation.- Monte Carlo Calculations of the Dimensions of Model Peptides and Peptide Hormones Related to Energy Transfer.- On the Relation Between Charge Redistribution and Intermolecular Forces in Models for Molecular Interactions in Biology.- Intermolecular Interactions in an External Electric Field: Application to the Analysis of the Evaluation of Interaction Energies from Field Mass Spectrometry Experiments.- Quantitative Structure Activity Relationships of Anthracycline Antitumor Activity and Cardiac Toxicity Based upon Intercalation Calculations.- A Model for Drug-Receptor Interactions: The Opiate Receptor. A Preliminary Report.- H-Bond-State and Solubility in Aqueous Systems. A Working Hypothesis.- Experimental Studies of Variations of the State of Water in Living Cells.- Structural Variations in a Homologous Series of Fluorinated Tetracyano-p-Quinodimethanes.- Interlayer Properties of Expanded Silicate Structures - New Calculational Approaches Concerning Intercalation.- Intermolecular Forces and Lattice Dynamics of Molecular Crystals.- The Motion of Particles Ahead of a Solidification Front.
TL;DR: In this article, the potential energy surface of the collinear abstraction reaction and the vertical insertion reaction were investigated, and the influence of the orbital basis size and electron correlation both on the reaction energy and on the barrier height and location for the abstraction reaction was investigated.
TL;DR: In this article, coupled Hartree-Fock perturbation theory is applied in extended ab initio calculations of molecular dipole moments, polarisabilities and first hyperpolarisabilities of first-row hydrides.
Abstract: Coupled Hartree-Fock perturbation theory is applied in extended ab initio calculations of molecular dipole moments, polarisabilities and first hyperpolarisabilities of first-row hydrides. Their dependence on internuclear separation is also analysed and discussed. Very strong hyperpolarisability gradients and large vibrational corrections are found. The relevance of the present results for interpreting the discrepancies between experimental and theoretical hyperpolarisabilities is pointed out.