Split-valence plus polarization

Concerning the VEE, we have chosen, as standard references for comparison, the EOM-CCSD results from Stanton et al. [56] and from Comeau and Bartlett [57]. Results from other very efficient state-of-the-art methods such as Exponentially Generated Cl or the now widely used CASPT2 could also have been used. In general, these are methods from which mean errors in VEE less than 0.2 eV might be expected provided that the basis set used is at least of split-valence plus polarization quality and it is augmented in a well-conditioned way to account for Rydberg states. 

IG and 6-3IG. These are commonly used split-valence plus polarization basis sets. These basis sets contain inner-shell functions, written as a linear combination of six Gaussians, and two valence shells, represented by three and one Gaussian primitives, respectively (noted as 6-3IG). When a set of six d-type Gaussian primitives is added to each heavy atom and a single set of Gaussian p-type functions to each hydrogen atom, this is noted as and... 

Optimization of the basis set for atoms inevitably introduces some bias towards the atomic description, although this effect is seldom noticeable in basis sets of the traditional types described in Sec. 4.2. Bias towards the atoms can appear, however, if very small ANO sets (or, presumably, cc sets) are used. An ANO set contracted to split-valence plus polarization, [3s 2p Id], is probably too contracted to provide a good description of molecular binding. In particular, the d NO may be quite different in shape from what is required to describe polarization and correlation in the molecule. At least two d orbitals should be included to properly allow for these effects. Hence ANO or cc basis sets smaller than, say, [4s 3p 2d] should probably not be used for molecular calculations. 

A DZP or split-valence plus polarization basis is a minimal basis for correlated calculations. 

A variation of G2 theory that uses reduced orders of Moller-Plesset perturbation theory in combination with a smaller basis set for the quadratic configuration correction is G2(MP2,SVP) theory.77 78 The SVP refers to the split-valence plus polarization basis, 6-31G(d), used in this QCISD(T) correction. In this theory the final energy is given by... 

The protonation of thiirane and thiirene was studied systematically by using basis sets ranging from minimal to split valence plus polarization quality. The 6-31G optimized geometries for... 

SVP Split valence plus polarization. Synonym for a (-+) DZP basis set, where only the valence AOs are split into inner and outer functions, such as the (- ) cc-pVDZ basis set of Dunning or the (->) 6-31G basis set of Pople. 

Abbreviations used t(0)dzp - basis set is double-zeta polarization on all atoms except oxygen for which it is valence triple-zeta svp - basis set is split-valence plus polarization. B3LYP, BP86, and PW are all gradient-corrected density functionals. See the original papers for references. 

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