Quadratic configuration interaction with

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],... 

Quadratic Configuration Interaction with Singles and Doubles Quadratic Configuration Interaction with Singles, Doubles, and Noniterative Approximation of Triples Symmetry Adapted Cluster-Configuration Interaction Split-Valence basis set plus Polarisation functions Zero-Order Regular Approximation Zero-Point Energy... 

QCISD Quadratic Configuration Interaction with Singles and Doubles... 

QCISD(T) quadratic configuration interaction with single and double excitation and... 

QCISD(T) Quadratic configuration interaction with single double and perturbative triple excitations... 

From an all-electron (quadratic configuration interaction with all single and double excitations) potential [22]. — For gaseous ND2 derived [23] from LMR [24] and lODR frequencies [25]. For NHD in a nitrogen matrix from an IR spectrum [20]. — For gaseous ND2 from an LMR spectrum [24]. 

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