Triple zeta plus polarization

In Table 1 we present the optimized geometries of both systems obtained at the HF level by using a triple zeta plus polarization basis set53 and at the MP2/6-31 + G(d,p)... 

A number of fullerenes have been the subject of fully ab initio theoretical studies, and no attempt will be made here to review this work. However, for any but the smallest fullerenes these remain tremendously challenging computations due to the shear size of the molecules. Were it not for the extremely high icosahedral symmetry of buckminsterfullerene, most of the ab initio calculations which have been performed on it would still be impossibly time consuming even with modem computational resources. Even the largest of these, such as the TZP-MP2 (triple zeta plus polarization basis with electron correlation at the Moeller-Plesset 2nd order level) calculation on buckminsterfullerene of Haser, Almlof, and Scuseria [3], are still short of the basis set and correlation levels normally desired to be confident that the calculation is converged to chemical accuracy. As a result, semiempirical theoretical methods have played, and likely will continue to play, a major role in theoretical work on fullerenes. 

Wetmore et al. have achieved impressive results with the use of Density Functional Theory (DFT) calculations on the primary oxidation and reduction products observed in irradiated single crystals of Thymine [78], Cytosine [79], Guanine [80], and Adenine [81], The theoretical calculations included in these works estimated the spin densities and isotropic and anisotropic hyperfine couplings of numerous free radicals which were compared with the experimental results discussed above. The calculations involve a single point calculation on the optimized structure using triple-zeta plus polarization functions (B3LYP/6-31 lG(2df,p)). In many cases the theoretical and experimental results agree rather well. In a few cases there are discrepancies between the theoretical and experimental results. 

The calculations on Ti2He were performed (30) using a basis set of triple zeta plus polarization quality, including / functions on Ti. For the singlet states, both restricted open-shell Hartree-Fock (ROHF) and FORS MCSCF reference wavefunctions were used, while ROHF reference wavefunctions were used for the triplet states. In order to account for dynamic electron correlation and obtain... 

The full Cl is impractical except as a reference because the number of determinants is asymptotically N . That means its application is possible only for small molecules and small basis sets. In praaice, calculations using 25 x 10 determinants for H O in a double zeta plus polarization (DZP) basis have been made and —10 determinants for CH3 in a triple zeta plus polarization (TZP) basis. ... 

These comparisons, and additional comparisons with other ab initio calculations, indicate that the harmonic frequencies for benzene have not been pinned down at the 10-20 cm 1 level by the previously mentioned ab initio calculations. In order to reduce inaccuracies in the harmonic force field, we have performed relatively large scale calculations using a valence triple zeta plus polarization basis set (pVTZ) in coupled-cluster calculations with single and double excitations (CCSD). These results, as well as comparisons with previous ab initio and recent density functional (156-157) results, are described elsewhere (108). 

A few quantum-chemical ab initio calculations predicted structure, stability, and some other molecular properties for the ion. SCF, CASSCF, and MRSD Cl calculations with various basis sets up to triple-zeta plus polarization quality gave repulsive potential curves for the ground state X (1cr) (2a) (3cr), energies of -848.9 (SCF) or -872.8 (Cl) kJ/mol, and a zero activation energy for the deprotonation (or exothermic charge-separation) reaction + [3, 4]. On the other hand, ground-state potential curves with a very... 

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