Showing papers on "Møller–Plesset perturbation theory published in 1983"

Ab initio second-order Moller-Plesset calculation of the vibrational spectra of cyclobutadiene and its isotopic derivatives

Abstract: Optimum geometry, nr frequencies, and intensities were calculated for cyclobutadiene and seven isotopically substituted derivatives with use of SCF/6-31G* and MP2/6-31G* wave functions. Theoretical spectra agree well with experimental where they are known, except that a result that had been interpreted as showing cyclobutadiene to be square is reinterpreted in terms of a mixture of two nonequivalent dideuterio rectangular structures.

A theoretical study of the properties of BH3NH3

Abstract: Borane monoammoniate (BH3NH3) has been studied using several ab initio electronic structure methods and Gaussian basis sets. Equilibrium geometries have been computed at the Hartree–Fock level and, using the electron‐correlated Mo/ller–Plesset perturbation method, carried out to third order (MP3) with double‐zeta polarized quality basis sets. The computed MP3 geometry is in close agreement with recent microwave data; electron correlation is found to be necessary for a proper description of the B–N distance. Hartree–Fock dipole moments and harmonic vibrational frequencies are presented and discussed. Mo/ller–Plesset perturbation theory carried out to fourth order with triple‐zeta plus polarization basis sets is used to compute a B–N dissociation energy of 34.7 kcal mol−1 and a (Hartree–Fock zero‐point corrected) rotational barrier of 2.065 kcal mol−1, which is in excellent agreement with the experimental value. Analysis of the dissociation energy as a function of perturbation order indicates that terms involving triple and quadruple substitutions are required in the dissociation energy.

Perturbation theory and electron correlation in extended systems: Cyclic polyene model

Abstract: The applicability of the finite-order many-body perturbation theory to the electron correlation problem in extended one-dimensional systems is examined. The cyclic polyenes CNHN, N = 4ν + 2, ν = 1, 2, …, with the DNh geometry as described by both the Pariser–Parr–Pople and Hubbard Hamiltonians, are employed to model the metallic-like one-dimensional systems. The second-order perturbation theory contributions to the correlation energy are obtained with three different partitionings of the Hamiltonian (Huckel, M⊘ller–Plesset, and Epstein–Nesbet). The third- and fourth-order contributions are also calculated in special cases. A comparison with other methods is given wherever available. For the Hubbard Hamiltonian the asymptotic behavior of the perturbation theory expansion is examined numerically. It is shown that the finite-order perturbation expansion can provide reliable results for the correlation energy of one-dimensional systems even in the correlation region which corresponds to the spectroscopically determined physical value of the coupling constant.

Multiconfigurational Hartree–Fock response functions

Abstract: The linear, quadratic, and cubic response of a multiconfigurational Hartree–Fock state to a time independent one-electron perturbation has been derived. A comparison between the exact response functions as obtained from Rayleigh–Schrodinger perturbation theory and the multiconfigurational Hartree–Fock response functions allows a identification of matrix elements of the perturbation operator between the ground and excited states and between excited states. We discuss some ambiguities which result from such an identification.

Extended basis CNDO calculations of linear and nonlinear electric susceptibilities of some molecular dianions and carbonions using coupled Hartree–Fock perturbation theory

Abstract: The results of calculating the average polarizabilities, first and second hyperpolarizabilities and molar Kerr constants of C5H, C6H, 2-C10H, 2-C14H, C8H and C8H are reported. The main elements of our computational scheme are McWeeny's coupled Hartree–Fock perturbation theory and an extended basis CNDO wave function. It is shown that the studied anions have nonlinearities within the same order of magnitude as their respective uncharged parent molecules. The Kerr constants of these anions are analyzed and the contribution of the various terms is appraised.

Perturbation theory of the electron correlation effects for atomic and molecular properties. V. Quadrupole polarizability of Ne

Abstract: The static quadrupole polarizability of Ne is calculated through the use of the many-body perturbation-theory scheme limited to single and double substitutions in the reference Hartree-Fock (HF) determinant (SD-MBPT). All calculations are performed within the finite-field numerical perturbation scheme. The fourth-order MBPT treatment based on the coupled HF solution for the perturbed system leads to the quadrupole polarizability value equal to 7.48 a.u. The convergence of the SD-MBPT series for properties and the role of the renormalization terms are discussed.

An ab initio calculation of three-particle correlation in Np3+

Abstract: A non-relativistic ab initio calculation of the six Judd (three-electron correlation) parameters Ti has been carried out using second- and third-order perturbation theory with a localised basis set. It is shown that the third-order perturbation contributions are significant and their inclusion considerably improves agreement between theoretical and experimental results.