Core-valence effects

Obtained by addition of the CBS results of (a) with the core-valence effects of (b). 

CBS plus core-valence effects of (c) with the addition of spin-orbit effects from Ref (46) (2-electron SO-PP values) Ref (42-44),... 

Another series of composite computational methods, Weizmann-n (Wn), with n = 1-4, have been recently proposed by Martin and co-workers W1 and W2 in 1999 and W3 and W4 in 2004. These models are particularly accurate for thermochemical calculations and they aim at approximating the CBS limit at the CCSD(T) level of theory. In all Wn methods, the core-valence correlations, spin-orbit couplings, and relativistic effects are explicitly included. Note that in G2, for instance, the single-points are performed with the frozen core (FC) approximation, which was discussed in the previous section. In other words, there is no core-valence effect in the G2 theory. Meanwhile, in G3, the corevalence correlation is calculated at the MP2 level with a valence basis set. In the Wn methods, the core-valence correlation is done at the more advanced CCSD(T) level with a specially designed core-valence basis set. 

This form for the one-electron matrix elements was suggested through an expansion of of Eq. [14b], The third term of Eq. [29a] and the third term of [29c] represent the two-center part of a core-valence effective potential introduced to compensate for the repulsive nature of the neglected core orbitals in a valence orbital only treatment. 

Core-Valence Effects for Systems Containing First Row Atoms B-F 586... 

CORE-VALENCE EFFECTS FOR SYSTEMS CONTAINING SECOND ROW ATOMS Na-Ar... 

The RECP approaches have shown considerable promise as they have provided powerful avenues for laige-scale computations that include both relativistic and electron correlation effects simultaneously. While the coupling of these effects, and especially, coupling of spin-orbit and correlation effects are taken into consideration quite accurately, the RECP techniques do not always yield accurate bond lengths, especially for the sixth-row compounds. This feature seems to depend on the RECPs, the technique used to generate RECPs, and the parameters used therein for the generation of the pseudo-orbitals. Other effects such as core-valence effects are also known to make substantial contributions to the properties of molecules, but these corrections can be incorporated in the RECPs. 

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