An adjustable contracted CI method

A new contracted CI scheme——adjustable contracted CI scheme——is presented and programed. The efficiency of this scheme is tested by some example calculations. The result shows that the application of the new scheme is flexible and the correlation energy loss is lower than that of the original externally contracted CI method.     

Computer aided drug identification in toxicological analysis by means of EI and CI mass spectrometry

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Computer aided drug identification in toxicological analysis by means of EI and CI mass spectrometry

     

SCF MO CI perturbation calculations of inner shell and valence shell vertical ionization potentials

A CI method for calculating inner and valence shell vertical ionization potentials is presented. It is based on ab initio SCF MO calculations for the neutral closedshell ground state followed by CI perturbation calculations for the ground and ion states including all spin and symmetry adapted singly and doubly excited configurations with respect to the main configurations of the state of interest. The state energy is computed by performing a CI calculation for a set of selected configurations, and then adding the contributions of the remaining configurations as estimated by second order Brillouin-Wigner perturbation theory. The use of the same set of MO's for all states together with the CI perturbation method makes the method rather rapid. The numerical results are, in spite of the limited Gaussian basis sets used, in good agreement with experiment.     

3p阶亚循环群的连通4度Cayley图

研究3p阶(p是大于3的素数)亚循环群的连通4度Cayley图.主要决定了其全自同构群的结构,并由此得到这类图的CI性、正规性和弧传递性.用到单群分类定理.     

Selected excitation for CAS-SDCI calculations

A new selected-configuration interaction method is proposed, based on the use of local orbitals. A corresponding code has been written, which is devoted to CI calculations of rather large systems (about 50-100 carbon-like atoms). Taking advantage of the locality, and then of the fact that interactions vanish when the distance is large, the dimension of the CI space is largely reduced. The determinants that would be created by long range excitations are expected to have a small weight in the wave function and are therefore eliminated. This selected excitation CI space is particularly suited for large molecules. It is tested on large polyene chains and on a transition metal complex. For large enough systems, the CPU time saving is important and, what is more noticeable, calculations that were impossible to perform without selection are feasible in this approach.     

CASSCF and multireference CI with singles and doubles study of low-lying valence and Rydberg states of 2H-tetrazole

Complete active space self-consistent field (CASSCF) and multireference CI with singles and doubles (MR-CISD) calculations [including extensivity corrections, at MR-CISD+Q and multireference averaged quadratic coupled cluster (MR-AQCC) levels] have been performed to characterize the low-lying valence and the Rydberg states of 2H-tetrazole. The highest level results (MR-AQCC/d'-aug'-cc-pVDZ) indicate the following ordering of the valence singlet excited states: S(1) (n-pi*), 6.06 eV; S(2) (n-pi*), 6.55 eV; S(3) (pi-pi*), 6.55 eV. The MR-CISD+Q/d'-aug'-cc-pVDZ results indicate the same ordering, but at slight higher energies: 6.16, 6.68, and 6.69 eV, respectively. According to our MR-CISD+Q/d'-aug'-cc-pVDZ results, the next two states are Rydberg states, at 7.69 eV (pi-3s) and 7.89 eV (n-3s). The calculated energies of these two states, as well as their proximity, are consistent with the conclusion reached by Palmer and Beveridge (Chem Phys 1987, 111, 249) that the first band of the photoelectron spectrum of 2H-tetrazole is likely to be associated to the first two ionizations processes (of pi and N lone pair electrons), at energies close to 11.3 eV.     

Quantum-chemical modeling of photoelectron spectra and electronic structure of <Emphasis Type="Italic">tris</Emphasis>-β-diketonates of 3<Emphasis Type="Italic">d</Emphasis>-metals Sc,Ti, V

The electronic structure and ionization energies of chelate complexes were calculated for transition metals Sc, Ti, and V using the Hartree-Fock (HF)SCF ab initio approximations. As the number of d electrons increases in the series of these compounds, the sequence of HF orbitals does not agree any longer with the PES bands and with the data obtained in the density functional theory approximation. Using the configuration interaction (CI) method considerably improves agreement with experiment. For the vanadium complex containing an odd d electron in the ionized state, the HF orbitals become a rough approximation for the CI decomposition, hindering the interpretation of the ionic states.Original Russian Text Copyright © 2004 by V. I. Vovna and I. S. OsmushkoTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 651–659, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

On the invariance of the configuration interaction energy with respect to orbital rotations

Summary The invariance of the configuration interaction (CI) energy with respect to orbital rotation is considered. The inclusion of all spin couplings versus only those from the first-order interacting space is considered. A definition for the analog of a second-order CI calculation when inactive electrons are present is proposed.