Dunning correlation-consistent basis sets

We have recently employed the Dunning correlation-consistent basis sets for our pair natural orbital CBS extrapolation algorithm, Eqs. (2.1) and (2.2) [50]. The results produced a substantial improvement over the raw second-order energies, but were inferior to the (lmax + ) 3 extrapolations listed in Table 4.4. The residual underestimation of... 

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). 

CO Peterson and Dunning [92] have made an extensive analysis of the role of basis sets and correlation treatments in the calculation of the molecular properties of CO. By carefully controlling the errors in the calculations, it was possible to compute properties of this small molecule to an accuracy that rivals the most sophisticated experimental studies. They made use of the correlation consistent basis sets (cc). The dissociation energy with icCAS+SDQ was computed 258.5 kcal/mol with the best method, and the experimental value is 259.6 0.1 kcal/mol. The CCSD(T) yielded 258.6 kcal/mol in excellent agreement with experiment. CASSCF, MP4, and CCSD yield results with errors bigger than 4 kcal/mol. The CBS limit was obtained by exponential extrapolation of the cc-pVDZ through cc-pV6Z for all methods. 

From the broad spectrum of atomic orbital basis sets, one type can be strongly recommended. It is the basis set library of Dunning and coworkers [5], the correlation consistent polarized valence XZ (cc-pVXZ, X = D, T, Q,. . . ) basis sets. Dunning s augmented sets of correlation consistent basis sets (aug-cc-... 

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). 

The correlation-consistent composite approach (ccCA) is based in part on the G3B method, but uses Dunning correlation-consistent basis sets instead of Pople basis sets, does extrapolations to the CBS limit, replaces the QCISD(T) calculation with a CCSD(T) calculation, includes a relativistic correction, and contains no empirical parameters [N. J. DeYonker et al., J. Chem. Phys., 125, 104111 (2006) Mol. Phys., 107,... 

Alternate basis sets that are commonly nsed are the Dunning correlation-consistent polarized valence X zeta basis sets, denoted cc-pVXZ, see Table 8.3. Dunning pointed out that basis sets optimized at the Hartree-Fock level might not be ideal for correlated computations [462]. The correlation consistent basis sets are optimized using correlated wavefunctions and cc-pVXZ means a Dunning correlation-consistent, polarized valence, X-zeta basis X=D,T,Q,5,6,7. In particular, the cc-pVDZ for C atom... 

Rappe, Smedley and Goddard (1981) Stevens, Basch and Krauss (1984) Used for ECP (effective core potentitil) calculations Dunning s correlation consistent basis sets (double, triple, quadmple, quintuple and sextuple zeta respectively). Used for correlation ctilculations Woon and Dunning (1993)... 

Electron correlation studies demand basis sets that are capable of very high accuracy, and the 6-31IG set I used for the examples above is not truly adequate. A number of basis sets have been carefully designed for correlation studies, for example the correlation consistent basis sets of Dunning. These go by the acronyms cc-pVDZ, cc-pVTZ, cc-pVQZ, cc-pV5Z and cc-pV6Z (double, triple, quadruple, quintuple and sextuple-zeta respectively). They include polarization functions by definition, and (for example) the cc-pV6Z set consists of 8. 6p, 4d, 3f, 2g and Ih basis functions. 

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. 

Dunning has developed a series of correlation-consistent polarized valence n-zeta basis sets (denoted cc-pVnZ ) in which polarization functions are systematically added to all atoms with each increase in n. (Corresponding diffuse sets are also added for each n if the prefix aug- is included.) These sets are optimized for use in correlated calculations and are chosen to insure a smooth and rapid (exponential-like) convergence pattern with increasing n. For example, the keyword label aug-cc-pVDZ denotes a valence double-zeta set with polarization and diffuse functions on all atoms (approximately equivalent to the 6-311++G set), whereas aug-cc-pVQZ is the corresponding quadruple-zeta basis which includes (3d2flg,2pld) polarization sets. 

For the related [CpIr(PH3)(CH3)]+ system, four basis sets were used. Basis set one (BS1) is the same as the ones described above for Ir and P, but the C and H are described as D95. Basis set two (BS2) is the Stuttgart relativistic, small core ECP basis set (49) augmented with a polarization function for Ir, and Dunning s correlation consistent double-zeta basis set with polarization function (50) for P, C and H. Basis set three (BS3) is the same as BS1 except the d-orbital of Ir was described by further splitting into triple-zeta (111) from a previous double-zeta (21) description and augmented with a f-polarization function (51). Basis set four (BS4) is the same as BS2 for Ir, P, and most of the C and H, but the C and H atoms involved in the oxidative addition were described with Dunning s correlation consistent triple-zeta basis set with polarization. 

The quality of quantum-chemical calculations depends not only on the chosen n-electron model but also critically on the flexibility of the one-electron basis set in terms of which the MOs are expanded. Obviously, it is possible to choose basis sets in many different ways. For highly accurate, systematic studies of molecular systems, it becomes important to have a well-defined procedure for generating a sequence of basis sets of increasing flexibility. A popular hierarchy of basis functions are the correlation-consistent basis sets of Dunning and coworkers [15-17], We shall use two varieties of these sets the cc-pVXZ (correlation-consistent polarized-valence X-tuple-zeta) and cc-pCVXZ (correlation-consistent polarized core-valence X-tuple-zeta) basis sets see Table 1.1. 

A variety of extrapolation algorithms have been applied to the sequences generated by the correlation-consistent cc-pVnZ basis sets [12, 51-55], Dunning and his colleagues had initially suggested fitting their calculations to an exponentially decaying function [12, 51, 52],... 

Dunning s correlation consistent basis sets cc-pVAZ [27] augmented with diffuse functions [28] were used in the calculations. We considered cardinal numbers X—D, T, Q, 5, 6 and single (s), double (d), triple (t), and quadruple (q) augmentations. The orbitals were not allowed to relax in the coupled cluster response calculations. 

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