Correlation consistent valence basis set

Martin, J.M.L., Sundermann, A. Correlation consistent valence basis sets for use with the Stuttgart-Dresden-Bonn relativistic effective core potentials The atoms Ga-Kr and In-Xe, J. Chem. Phys. 2001,114,3408. 

Augmented Correlation Consistent Valence Basis Sets... 

Table 6 First Four Augmented Correlation Consistent Valence Basis Sets for Hydrogen, Helium, and the First-row Atoms Boron through Neon...

Correlation-consistent polarized basis sets are another popular choice, so called because they have been optimized using correlated (CISD) wavefunctions. These basis sets are labeled with the prefix cc-p before the valence zeta notation. They can then be augmented with diffuse functions, to give aug-cc-pVDZ, for... 

Stuttgart pseudopotential for Au with a uncontracted (lls/10p/7d/5f) valence basis set and a Dunning augmented correlation consistent valence triple-zeta sets (aug-cc-pVTZ) for both C and N, but with the most diffuse f function removed, was used. 

Del Bene, J. E., and Shavitt, I., Basis-set effects on computed acid-base interaction energies using the Dunning correlation-consistent polarized split-valence basis sets, J. Mol. Struct. (Theo-chem) 307, 27-34 (1994). 

A justification for this approximation is that the inner-shell electrons of an atom are less sensitive to their environment than the valence electrons. Thus the error introduced by freezing the core orbitals is nearly constant for molecules containing the same types of atoms. In fact, it is often preferable to employ the frozen core approximation as a general rule because most of the basis sets commonly used in ab initio quantum chemistry do not provide sufficient flexibility in the core region to accurately describe the correlation of the core electrons. Recently, Woon and Dunning have attempted to alleviate this problem by publishing correlation consistent core-valence basis sets.125... 

Obviously, the first consideration one must address when performing population analysis is the reliability of the wavefunction at hand. Whereas this topic is well beyond the scope of this review, a quick scan of the populations reported in this chapter indicates that basis set size and elearon correlation play an important role in defining the electronic distribution. For most compounds, a split-valence basis set augmented with polarization functions on the heavy atoms is the smallest basis set that produces reasonably consistent populations, regardless of the population method employed. One should further keep in mind the effects of electron correlation. Generally correlation contracts the core electrons, lengthens bonds, and reduces the ionic component of bonds. 

As an example for the typical quality of molecular properties obtained with the newly developed basis sets of Martin and Sundermann [241] the results for the energy-consistent large-core Ge pseudopotential for the diatomics GeH, GeO and GeF is displayed in Table 8. In addition to their work on main group PP basis sets Martin and Sundermann [241] also proposed (2flg) correlation sets to be used with the (8s7p6d)/[5s4p3d] valence basis sets of the transition... 

The DFT calculations were done with the deMon code [42] on a Cray C94. The set of auxihary basis functions is (3,4 3,4) for Pd and (4,4 4,4) for C and O [43], The orbital basis sets are Dunning s correlation-consistent Valence Triple-Zeta basis sets (cc-pVTZ) on C and O, and (2211/2111/121) for Pd [44], where only s-, p- and (six components) d-type functions were retained. The Pd atoms are treated as -i-16 electron atoms, using a... 

J. E. Del Bene and I. Shavitt, Basis-Set Effects on Computer Acid-Base Interaction Energies Using the Dunning Correlation-Consistent Polarized Split-Valence Basis Sets, J. Mol Struct, (THEOCHEM) 307, 27-34 (1994). 

In this research, the coupled-cluster single and double substitutions method with a perturbative treatment of triple excitations CCSD(T) [16-18] was adopted based on unrestricted Hartree-Fock reference wave functions. For the CCSD(T) computations, the cc-pVDZ, cc-pVTZ, and cc-pVQZ quality basis sets were used, where cc-pVnZ is an abbreviation for the correlation-consistent polarized valence basis sets of Dunning et al. [19-22]. With the coupled-cluster methods used in this research, the core orbitals are frozen. That is, the Is-like molecular orbital is frozen for O, while the Is2s2p3s3p3d-like molecular orbitals are frozen for Br. 

Other, scalar relativistic effects are usually minor. Among them, the most important is the contraction of s-orbitals caused by the increase in electron mass due to high velocity near the nucleus. Except in the most careful work, such effects are modeled using relativistic effective core potentials (ECPs), also called core pseudopotentials [76]. When an ECP is used, the corresponding valence basis set should be used for the remaining electrons. A small-core ECP, in which fewer electrons are replaced by the effective potential, is a weaker approximation and therefore more reliable than the corresponding large-core ECP. The selection of basis sets to accompany ECPs is more restricted than the selection of all-electron basis sets, but appropriate correlation-consistent basis sets are available for heavy p-block elements [77-80]. 

Dunning s augmented correlation-consistent valence double- basis set, aug-cc-pVDZ." " Of these approaches, CCSD(T) is considered the most sophisticated and reliable. 

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