Angela K. Wilson

Gaussian basis sets for use in correlated molecular calculations. IX. The atoms gallium through krypton

Valence correlation consistent and augmented correlation consistent basis sets have been determined for the third row, main group atoms gallium through krypton. The methodology, originally developed for the first row atoms, was first applied to the selenium atom, resulting in the expected natural groupings of correlation functions (although higher angular momentum functions tend to be relatively more important for the third row atoms as they were for the second row atoms). After testing the generality of the conclusions for the gallium atom, the procedure was used to generate correlation consistent basis sets for all of the atoms gallium through krypton. The correlation consistent basis sets for the third row main group atoms are as follows: cc-pVDZ: (14s11p6d)/[5s4p2d]; cc-pVTZ: (20s13p9d1f )/[6s5p3d1f]; cc-pVQZ: (21s16p12d2 f1g)/[7s6p4d2 f1g]; cc-pV5Z: (26s17p13d3f2g1h)/[8s7p5d3f2g1h]. Augmented sets were obtained by adding diffuse functions to the above sets (one for each angular momentum present in th...

BASIS-SET CONVERGENCE IN CORRELATED CALCULATIONS ON NE, N2, AND H2O

Valence and all-electron correlation energies of Ne, N2, and H2O at fixed experimental geometries are computed at the levels of second-order perturbation theory (MP2) and coupled cluster theory with singles and doubles excitations (CCSD), and singles and doubles excitations with a perturbative triples correction (CCSD(T)). Correlation-consistent polarized valence and core-valence basis sets up to sextuple zeta quality are employed. Guided by basis-set limits established by rij-dependent methods, a number of extrapolation schemes for use with the correlation-consistent basis sets are investigated. Among the schemes considered here, a linear least-squares procedure applied to the quintuple and sextuple zeta results yields the most accurate extrapolations.

Gaussian basis sets for use in correlated molecular calculations. X. The atoms aluminum through argon revisited

For molecules containing second row atoms, unacceptable errors have been found in extrapolating dissociation energies calculated with the standard correlation consistent basis sets to the complete basis set limit. By carefully comparing the convergence behavior of De(O2) and De(SO), we show that the cause of these errors is a result of two inter-related problems: near duplication of the exponents in two of the d sets and a lack of high-exponent functions in the early members of the sets. Similar problems exist for the f sets (and probably in higher angular momentum sets), but have only a minor effect on the calculated dissociation energies. A number of approaches to address the problems in the d sets were investigated. Well behaved convergence was obtained by augmenting the (1d) and (2d) sets with a high-exponent function and by replacing the (3d) set by the (4d) set and the (4d) set by the (5d) set and so on. To ensure satisfactory coverage of both the L and M shell regions, the exponents of the new d se...

GAUSSIAN BASIS SETS FOR USE IN CORRELATED MOLECULAR CALCULATIONS. VI. SEXTUPLE ZETA CORRELATION CONSISTENT BASIS SETS FOR BORON THROUGH NEON

Abstract The family of correlation consistent polarized valence basis sets (cc-pVXZ) has been extended to include sextuple zeta sets (cc-pV6Z) for the atoms boron through neon. Potential energy functions have been calculated with these sets for the electronic ground states of N2 and HF using a number of correlated wave functions: MP2, MP3, MP4, CCSD, CCSD(T) and CAS+1+2. Spectroscopic constants have been calculated for each level of theory and have been compared with experiment. Combining these results with those of prior studies, complete basis set limits have been estimated for Ee, De and re. It is found that the cc-pV6Z basis sets yield dissociation energies that are within 0.6–0.8 kcal mol−1 (N2) and 0.1 kcal mol−1 (HF) of the estimated CBS limits. Adding core-core and core-valence contributions to the CCSD(T) CBS limits yields Des that are within 0.1 kcal mol−1 of the experimental values.

Benchmark calculations with correlated molecular wave functions. X. Comparison with “exact” MP2 calculations on Ne, HF, H2O, and N2

The convergence of the MP2 valence correlation energy and pair energies for the correlation consistent basis sets has been investigated. Ne, HF, H2O, and N2 were studied. For all of these molecules, accurate MP2 correlation and pair energies are available from the recent MP2-R12 calculations of W. Klopper [J. Chem. Phys. 102, 6168 (1995)]. The magnitudes of the calculated MP2 valence correlation and pair energies are found to increase systematically with increasing basis set size, with the cc-pV6Z basis set yielding 97.4%–98.3% of the MP2 valence correlation energy. A detailed analysis of the results for Ne reveals that the error due to truncation of the radial functions in the cc-pV6Z set is comparable to that due to neglect of higher angular momentum functions. Procedures for extrapolating the results to the complete basis set limit have also been investigated.

The Effect of Basis Set Superposition Error (BSSE) on the Convergence of Molecular Properties Calculated with the Correlation Consistent Basis Sets

It is shown that, in many cases, the convergence behavior of molecular properties computed with the correlation consistent basis sets (both standard and augmented sets) is significantly improved if basis set superposition error (BSSE) is taken into account. The effects are most pronounced for pure van der Waals systems like the helium or argon dimers. For these systems the uncorrected D e , r e , and ω e behave very irregularly with increasing basis set size, with the convergence behavior being dramatically improved by use of the counterpoise procedure. Even for strongly bound diatomics like N 2 , HF, and HCl, the counterpoise correction often significantly improves the convergence behavior of r e and ω e . Similar behavior is observed in the weakly bound molecular complexes, ArHF, HCO − , and (HF) 2 , as well as for the more strongly bound HCO molecule. For HCO − , because of the pronounced lengthening of the CO bond upon molecular formation, the deformation energy must also be taken into account.