Single-double configuration interaction calculations

To check the influence of correlation energy on the analysis performed, single reference configuration interaction calculations [hereafter referred to as Single plus Double Configuration Interaction (SDCI)] have been carried out on the compound Fe CO)i 7i -CH2O), by using the direct-CI method [3]. 58 electrons have been frozen because of the dimensions... 

There is also a hierarchy of electron correlation procedures. The Hartree-Fock (HF) approximation neglects correlation of electrons with antiparallel spins. Increasing levels of accuracy of electron correlation treatment are achieved by Mpller-Plesset perturbation theory truncated at the second (MP2), third (MP3), or fourth (MP4) order. Further inclusion of electron correlation is achieved by methods such as quadratic configuration interaction with single, double, and (perturbatively calculated) triple excitations [QCISD(T)], and by the analogous coupled cluster theory [CCSD(T)] [8],... 

Another class of methods uses more than one Slater determinant as the reference wave function. The methods used to describe electron correlation within these calculations are similar in some ways to the methods listed above. These methods include multiconfigurational self-consistent field (MCSCF), multireference single and double configuration interaction (MRDCI), and /V-clcctron valence state perturbation theory (NEVPT) methods.5... 

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. 

Multireference Briliouin-Wigner cou/ded cluster singles and doubles (MRBWCCSDJ and multireference doubles configuration interaction (MRD-CI) calculations for the Bergman cyclization reaction... 

H + CH2 CH3 This reaction has been the subject of several experimental [11] and theoretical studies [12]. The published theoretical work calculated portions of the hindered rotation barriers for different values of Rh-C Ihe distance of the attacking H from CH2. This calculation employed a tzp basis set [13] with an multireference singles and doubles configuration interaction (MRSDCI) wavefunction and was carried out with the COLUMBUS program system [14]. This work has now been supplemented by a much more extensive mapping of the hindered rotational potential with a less expensive dzp basis set [13], Tests show that Vtr is not sensitive to dzp or tzp basis set selection. 

MULTIREFERENCE BRILLOUIN-WIGNER CONFIGURATION INTERACTION CALCULATIONS WITH SINGLE AND DOUBLE SUBSTITUTIONS... 

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]. 

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