Single/double excitation configurational interaction calculations

Modular FORTRAN programs for performing general ab initio multireference single- and double-excitation configuration interaction, averaged coupled-pair functional and linearized couple-cluster method calculations. Cray and other versions. 

Thomas et al. have carried out extensive calculations on the two unknown, unsubstituted, tetrazines, as well as on 1,2,4,5-tetrazine. SCF calculations including double zeta (DZ), and DZ plus polarization (DZP) basis sets, as well as single and double excitation configuration interaction (CSID) levels of theory were used. They have calculated relative energies (AE) by these methods, the results being given in Table 1 <9lJOC539>. 

In their study of the lowest part of the Ceo Hubbard spectrum, FKS carried out single and double excited configuration interaction (SDCI) calculations. These were based on an appropriate set of reference configuration state functions constructed by means of a set of restricted Hartree-Fock (RHF) orbitals. Although, as FHS point out, a SDCI treatment is not size consistent, one can anticipate obtaining significant information with regard... 

QCISD(T) quadratic configuration interaction calculation, including single and double-substitutions and non-iteratively triple excitations R2 correlation coefficient... 

Configuration interaction calculations including single and double excitations (CISD) were carried out on the QC using as reference state (reference Slater determinant) the one obtained by the previous B3LYP/BS ground state evaluation and... 

For heavier triatomic systems, Flartree-Fock potential surfaces had earlier been calculated for FI + NO- FfNO [120] andO + NO [121]. Recently Pipano and Kaufman [122] performed an ab initio large-scale configuration-interaction calculation for the reaction 0+ + Na - NO+ + N that included all single and double excitations relative to the lowest configurations of the 2n(, 2 +, 4n, states of the intermediate NNO+ as a function of internuclear distance. These results, as an example of the melding together of the way the theoretical techniques outlined earlier complement each other and experimental observations, will be discussed in more detail in Section IV of this chapter. 

Refs. [44, 46, 49, 51], the second- and third-order approximate coupled cluster (CC2 and CC3) calculations of Ref. [50], the equation of motion coupled cluster with single, double and perturbative triple excitations calculations of Ref. [45], the symmetry adapted cluster configuration interaction calculations of Ref. [48] and the time-dependent density functional theory calculations using the B3LYP functional of Ref. [39]. 

The most accurate allowance for the correlation effects was made by Schaefer et al. [59]. An SCF calculation was supplemented by inclusion of the complete configurational interaction among all the single- and double-excited configurations (37528 for C2V structure and 74740 for the form). A lowering of the barrier was 2.9 kcal/mol and the allowance made for higher excitations added to this value 0.5 kcal/mol to give ultimately 8.1 kcal/mol. 

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