Aug-cc-pVTZ

CCSD(T)/aug-cc-pVTZ Atomization energy 5 kcal/mol mean abs. dev. 

We will now look at how different types of wave functions behave when the O-H bond is stretched. The basis set used in all cases is the aug-cc-pVTZ, and the reference curve is taken as the [8, 8J-CASSCF result, which is slightly larger than a full-valence Cl. As mentioned in Section 4.6, this allows a correct dissociation, and since all the valence electrons are correlated, it will generate a curve close to the full Cl limit. The bond dissociation energy calculated at this level is 122.1 kcaPmol, which is comparable to the experimental value of 125.9 kcal/mol. 

The HF method overestimates the barrier for linearity by 0.73 kcal/mol, while MP2 underestimates it by 0.76 kcal/mol. Furthermore, the HF curve increase slightly too steeply for small bond angles. The MP4 result, however, is within a few tenths of a kcal/ mol of the exact result over the whole curve. Compared to the bond dissociation discussed above, it is clear that relative energies of conformations which have similar bonding are fairly easy to calculate. While the HF and MP4 total energies with the aug-cc-pVTZ basis are 260 kcal/mol and 85 kcal/mol higher than the exact values at the equilibrium geometry (Table 11.8), these errors are essentially constant over the whole surface. 

From a basis set study at the CCSD level for the static hyperpolarizability we concluded in Ref. [45] that the d-aug-cc-pVQZ results for 7o is converged within 1 - 2% to the CCSD basis set limit. The small variations for the A, B and B coefficients between the two triple zeta basis sets and the d-aug-cc-pVQZ basis, listed in Table 4, indicate that also for the first dispersion coefficients the remaining basis set error in d-aug-cc-pVQZ basis is only of the order of 1 - 2%. This corroborates that the results for the frequency-dependent hyperpolarizabilities obtained in Ref. [45] by a combination of the static d-aug-cc-pVQZ hyperpolarizability with dispersion curves calculated using the smaller t-aug-cc-pVTZ basis set are close to the CCSD basis set limit. 

Combining [52] the zero point vibrational corrections of Ref. [51] with the CCSD results obtained in the t-aug-cc-pVTZ and d-aug-cc-pVQZ basis sets we obtained the estimates for the ZPV corrected 70, A and B coefficients listed in Table 4. An experimental estimate for 70, A, and B has been derived by Shelton by fitting the results of ESHG measurements to the expresssion = To(l + A0JI2 + This... 

Computations at the level of CCSD(T)/(aug-)cc-pVTZ are, however, very much time consuming and in the following instanton calculations the best level of theory employed is CCSD(T)/(aug-)cc-pVDZ. 

To study the accuracy of the above result we estimated the splitting for the higher CCSD(T)/(aug) cc-pVTZ level of electronic structure theory. The full... 

Figure 13. Potential energy diagram of stationary points of the CHj + O reaction. The results are from CCSD(T)/aug-cc-pvtz//CCSD(T)/cc-pvdz calculations including zero point energy. Reprinted with permission from [67]. Copyright 2001 American Chemical Society.

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. 

FIGURE 2.1 Geometries of the reactants (11-16) and transition structures (S1-S6) at B3LYP level of theory in gas phase, using 6-3 lG(d), 6-311+ G(d,p) (bold characters), 6-311+ G(d,p), S(2df) (underlined), aug-cc-pVTZ (italic) basis sets, and in aqueous solution at B3LYP-C-PCM/6-311 + G(d,p) level of theory (bold characters in parenthesis). Bond length data have been taken from Ref. [13]. 

G(d,p), both intermediate and TS geometries become more reliable, at least as judged from a comparison with the corresponding geometries achieved using the augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) basis sets.32... 

In fact, it has been demonstrated that geometrical features of stationary points (including the hydrogen bonded complexes) optimized at 6-311 +G(d,p) are very similar to those obtained with the very large, but too time-consuming, aug-cc-pVTZ basis.f... 

This observation suggested that refining energies by single-point calculations with the aug-cc-pVTZ basis set on 6-311 + G(d,p)-optimized geometries is a reliable practice. 

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