Search

The aim of the present theoretical work is to provide data necessary for a better understanding of the electronic spectrum of the silane molecule, which is affected by the Jahn-Teller effect. By selecting an adequate distorted C2v geometry of SiH4, the three lower Koopmans ionization potentials are evaluated with the equation of motion coupled cluster of singles and doubles method. Vertical excitation energies for the different Rydberg series converging to the three Jahn-Teller components are inferred from ab initio coupled cluster linear response calculations. Absorption oscillator strengths for dipole-allowed electronic transitions are also determined with the molecular-adapted quantum defect orbital methodology. Predictions of new spectroscopic data on SiH4 are reported. [ABSTRACT FROM AUTHOR]

The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and quadrupole moments have also been calculated. The results provide a set of benchmark values for energies, wave functions, properties, and transition properties for the five electron BeH molecule. Most of the states have large multiconfigurational character in spite of their essentially single excited nature and a number of them present an important Rydberg-valence mixing that is achieved through the mixed nature of the particle MO of the single excitations. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [ABSTRACT FROM AUTHOR]

The size-consistent self-consistent configuration interaction method, (SC)2-CI, is a procedure based on the matrix dressing formulation of the intermediate hamiltonian theory, which aims to correct the size-extensivity problem in truncated or selected configuration interaction (CI) calculations. Corrected energies and CI-like functions are obtained. In the present paper, a procedure is proposed to get size consistent mean values of properties from the (SC)2 -SR-SDCI vectors. It can be easily extended, though in a less rigorous way, to (SC)2 -MR-SDCI functions. Calculations have been performed in 13 trial systems to test the size consistency behaviour of mean value one-electron properties obtained from (SC)2 vectors and the accuracy limits of the procedure. Properties for ground and excited states have been tested in the SR-SDCI, (SC)2 -SR-SDCI, MR-SDCI, and (SC)2 -MR-SDCI approximations. The dipole and quadrupole moments of several small molecules have been calculated with the corrected (SC)2 -SR-SDCI method. The values are compared to experimental and theoretical reference values. [ABSTRACT FROM AUTHOR]