Complete Configuration Interaction Method Research Articles

Precision calculation of the low-lying excited states of the Rf atom

Precision calculations of the ground and low-lying excited electronic states of the Rf atom (Z = 104) were performed. The relativistic effects were taken into account with the Dirac-Coulomb-Breit Hamiltonian. The finite nucleus size was taken into account in the Fermi model (A = 267). The correlation effects were described by the combined scheme that we suggested previously, which proved to be efficient: The relativistic coupled clusters method with one- and two-particle cluster amplitudes in the Fock space was used for describing the correlations of 44 outer electrons of the Rf atoms in a fairly large atomic basis set, and for the four valence electrons occupying the 7s, 7p, and 6d states, the contributions from three- and four-particle cluster amplitudes were taken into account using the complete configuration interaction method, but in a relatively small basis set. The relativistic configuration and term for the ground state of the Rf atom were refined, and the energies of its excitation to low-lying states were calculated. The accuracy of the calculation by the generalized relativistic effective core potential method was evaluated by comparing the results with those obtained similarly using the Dirac-Coulomb-Breit Hamiltonian.

Electric properties of alternate and nonalternate hydrocarbons studied by the complete configuration interaction method

Electric properties of alternate and nonalternate hydrocarbons studied by the complete configuration interaction method

?-Electron hyperpolarizability of even-numbered polyenes in the complete configuration interaction method

It has been established that the second hyperpolarizability of short polyenes with 2–10 carbon atoms increases in proportion to N3.95 in the complete configuration interaction method, and in proportion to N5.97 in the restricted Hartree-Fock method.

A study of interaction of two ethylene molecules by the semiempirical complete configuration interaction method in ?-electron approximation

The semiempirical complete configuration interaction method in π-electron approximation has been used to calculate the energies of states of a system composed of two interacting ethylene molecules and having the D2h symmetry. Oscillator strengths for the allowed transitions have been also calculated. If conjugation effects between the ethylene molecules are disregarded the hypochromism found by Nesbet is not obtained in this higher approximation. Consideration of conjugation effects results in hypochromism of the longest-wavelength allowed transition. The bathochromic shift of this band occurs at smaller distances between the two ethylene molecules than the hypochromic effect. Some general features of transannular interaction and the role of conjugation effects in the hypochromism of helical polynucleotides are discussed. The qualitative similarity of the cyclobutadiene energy spectra calculated by the semiempirical and by the theoretical methods of complete configuration interaction is pointed out.