Aug-cc-pVXZ

The tables below give some examples of atomic charges and bond orders calculated by various methods as a function of the basis set at the HF level of theory. It is evident that the Mulliken and Ldwdin methods do not converge as the basis set is increased, and the values in general behave unpredictably. Especially the presence of diffuse functions lead to absurd behaviours, as the aug-cc-pVXZ basis sets illustrate for CH4. Note also that... 

Table 11.10 establishes that diffuse functions are mandatory for calculating dipole moments, and only results with the aug-cc-pVXZ basis sets are shown for the DFT methods in Table 11.12. 

The experimental value for the dipole moment of CO is 0.122 D, with the polarity C 0+, for a bond length of 1.1281 A. Calculated values with the aug-cc-pVXZ basis sets are given in Table 11.21. Some other results using other basis sets are shown in Table 11.22. 

Figure 2 The valence correlation energies of Ne obtained by the CC or CC-R12 methods and the aug-cc-pVXZ basis sets (abbreviated as aXZ) [35].

A more sequential approach to the analysis of the systematic error of ab initio methods has been proposed in [14]. The same set of molecules as in [10] has been analyzed there. For this set the series of calculations using the basis sets aug-cc-pVxZ containing both polarization and diffuse functions with the number of exponents x in their respective radial parts up to x = 6 (single zeta x = 1, double zeta - DZ -x = 2, triple zeta - TZ - x = 3, etc.) and with the account of correlation effects in the range of methods from MP2 up to CCSD(T) had been performed and then fitted to the formulae [15-18] ... 

For various intermolecular complexes, it has been found that KSCED interaction energies converge rather rapidly with both the number of atomic centers and the atomic basis sets. Table 3 collects the KSCED results (interaction energy and the energy of the highest occupied orbital in one of the monomers) for two series of the basis sets (CC-PVxZ and AUG-CC-PVxZ, for x=2-5) applied in the KSCED(s) or KSCED(m) schemes for the CH4-CH4 complex. 

P = Ibar, temperature T = 273.15K, electric field strength E = 2.6 x IC/ V m , magnetic induction field B = 3 T. The acronym nXZ is a shorthand notation for the correlation consistent n-aug-cc-pVXZ basis set. Wf is the wave function model employed. From [40]... 

Figure 6. Dependence of the HF and MP2 formation energy (in kcal/mol) on the basis set size. Upper row. HF for the cc-pVxZ and aug-cc-pVxZ basis sets. Lower row MP2 values for the same basis sets. Empty symbols are for formation energies whose BSSE has not been corrected, while filled circles are for BSSE-corrected values (see text).

Figure 14. Variation of the MP2 BSSE-uncorrected and BSSE-corrected interaction energies of the methane-water complex with the basis set. Circles indicate results obtained using Pople basis set, while squares indicate results obtained with the aug-cc-pVxZ basis sets. The geometry is the optimum one computed at the MP2/aug-cc-pVTZ level.

Structure cc-pVXZ sets aug- -cc-pVXZ sets CCSD(T) (cc-pCVQZ) mc-qdpt (aug-cc-pVDZ)... 

A study of atomization energies of 66 small molecules with the aug-cc-pVxZ (x = D,T, Q) basis sets gave the following average absolute errors in kcal/mol [D. Feller and K. A. Peterson, J. Chem. Phys., 108,154 (1998)], where the letters D, T, Q denote the basis set ... 

MP2 calculations with large aug-cc-pVxZ basis sets yielded an estimate of -5.0 0.1 kcal/mol for the binding energy of the water dimer in the complete basis-set limit and the effect of going to the MP4 level was found to be negligible [M. W. Feyereisen, D. Feller, and D. A. Dixon,/. Phys. Chem., 100,2993 (1996)] essentially the same result was found by a method called symmetry-adapted perturbation theory, which treats the interactions between the monomers as a perturbation [E. M. Mas and K. Szalewicz, /. Chem. Phys., 104,7606 (1996)]. 

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