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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]

In previous works, the size-consistent self-consistent matrix dressing method has been applied to single reference as well as to complete active space singles and doubles configuration interaction. The wave function of the dressed state was assumed to be dominated by a closed shell determinant. Here, the method has been extended to systems where the dressed state is a single-configurational doublet. The method allows for the accurate calculation of energies and wave functions of other electronic states of the same system, having or not the same symmetry, as well as in the case of closed shell systems. This statement has been thoroughly assessed by the calculation of vertical ionization energies corresponding to a few low lying states of HF[sup +] that are compared to full CI results obtained with the cc-pVDZ basis set. The method has been applied, using larger basis sets, to the calculation of vertical ionization potentials (VIP) of HF, H[sub 2]CO, N[sub 2], and NH[sub 3]. The results are compared to experimental VIP values. The effects of selecting different CAS spaces and using pseudonatural adapted MO's obtained from the CASSCF matrix densities are shown and discussed. Mean absolute error (MAE) for the calculated states is about 0.07 eV. The difficulties to improve this precision limit are shown. However, the mean signed absolute errors, that measure accuracy, can be made smaller. Small MAE can be obtained using simultaneously VTZ basis sets and intermediate levels of calculation. The possibility of this effect to be assigned to a fortuitous cancellation of errors is pointed out. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]