Peter Swanstrøm

Calculation of molecular one-electron properties using coupled Hartree-Fock methods

A review of the coupled Hartree-Fock method for calculation of second-order one-electron properties is given with special reference to force constants and static electric and magnetic properties. A comprehensive analysis of the computational problems is attempted and we present the logic of a computer programme. A number of results obtained for the H2O molecule are reported in part II of this work.

Calculation of molecular one-electron properties using coupled Hartree-Fock methods: II. The water molecule

Various second-order properties for H2O have been computed using a near Hartree-Fock gaussian wave function and a coupled Hartree-Fock scheme. Satisfactory agreement with experimental data is obtai...

Photoionization cross sections involving an explicitly correlated initial state: Combination of multiconfigurational linear response and the stieltjes—tchebycheff moment theory

Abstract We have performed outer valence photoionization cross section calculations for N 2 and O 2 . To do this we have combined several linear response techniques, in particular time-dependent Hartree—Fock (TDHF), multiconfigurational time-dependent Hartree—Fock (MC TDHF), and a modification of MC TDHF (MMC TDHF) with Stieltjes—Tchebycheff moment theory (STMT). To our knowledge, these MC TDHF and MMC TDHF calculations are the first which combine explicitly correlated Green function approaches with STMT. Since, in addition, these calculations are fully coupled, we expect the MC TDHF and in particular the MMC TDHF—STMT results to be highly reliable. For both N 2 and O 2 our MC TDHF—STMT and MMC TDHF—STMT results are in overall agreement with previous static exchange STMT results; however, there are a few significant differences and differences in detail in the partial and total photoionization cross sections. In particular, for example, for N 2 we note that the MMC TDHF—STMT does not give a “hump” resonance in the cross section for the (1π u −1 )A 2 Π u ionic state. In O 2 we note that the (3σ g −1 ) cross section obtained using MMC TDHF—STMT is substantially lower than the static exchange results.

Calculation of harmonic force constants from Hartree-Fock-Roothaan wavefunctions

Some current methods of non-empirical computation of force constants are discussed; emphasis is given to the complete, analytical evaluation. It is shown that force constants evaluated to the Hartree-Fock limit are correct through first order in the error of the wavefunction. The consequences of using well-optimized wavefunctions are investigated in some detail. Some of the aspects are illustrated by exploratory calculations on H2.

Analytical ab initio computation of force constants and dipole moment derivatives: LiH, Li2 and BH

Ab initio calculations of harmonic force constants and dipole moment derivatives have been performed for the diatomic molecules LiH, Li2 and BH, using Hartree-Fock perturbation theory for a series of spherical gaussian SCF-MO wavefunctions. The results of these computations support the conclusion made in a previous paper that the so-called general method of calculation is the most reliable. The results obtained with the energetically best wavefunctions are (experimental values in parentheses, atomic units throughout): Force constants: LiH 0·071 (0·066); Li2 0·019 (0·016); BH 0·210 (0·196). Dipole moment derivatives: LiH - 0·48 (-0·42±0·06); BH - 0·67 (-0·4).

Structures and rearrangement reactions of oxaferretane (C2H4OFe): a theoretical approach

The photochemical rearrangement reactions of oxaferretane (3) have been investigated using ab initio methods. The geometry and electronic structure of both the substrate and of the products, an oxoiron–ethylene π complex (4) and vinyliron hydroxide (5), have been determined. From calculations of the excited states of (3) and (4) a mechanism for the photochemical rearrangement reaction (3)→(4)→(5) is suggested. The results obtained are discussed in relation to other oxo-transfer reactions.