Double zeta quality basis sets

We have used the systems CnH +2 with n = 2,4,...,22, C H +2 with n = 3,5,...,21, and C H +2 with n = 4,6,...,22 to represent pure PA, positively charged solitons, and bipolarons respectively. SCF wavefunctions were calculated with a double-zeta quality basis set (denoted 6-3IG) and optimized geometries for all these systems were determined. In addition for the molecules with n up to 11 or 12 we calculated the vibrational spectrum, including infrared and Raman intensities. 

Owing to computational limitations, the model used to represent the first shell of CA was the (NH3)3M (H20) system. This complex has been widely used in ab initio calculations of different mechanistic aspects of the CA enzyme [31]. Furthermore, the validity of this model, where the three imidazole ligands are substituted by three ammonia groups, has been previously assessed [31e, 32]. In the present study, full geometry optimizations of all eight minima with no symmetry constraints were performed. Pseudopotential wave functions have been preferred to full-electron calculations, because valence Similarity can be more easily related to reactivity than all-electron Similarity [33]. Dunning s valence double zeta quality basis set [34] together with the Hay and Wadt ECPs... 

An attempt at an ab initio calculation of the pNA hyperpolarizability by Sim et a/.38 using double zeta quality basis sets with diffuse polarizing functions within the finite field/HF/MP2 regime gave values which are even lower than those obtained by the semi-empirical methods. These calculations are at zero frequency but have been corrected to 1064 nm using the usual two state model. Bartlett and Sekino90,91 have discussed the relationship between hyperpolarizabilities calculated by ab initio methods and by SOS formalisms. They conclude that only the most powerful recent methods for correlated calculations can be expected to produce accuracy of about 10% for gas phase hyperpolarizabilities, while ab initio calculations interpreted in terms of the SOS expansion give very poor results when the equivalent number of states is small. 

The quantum chemical studies of the stmcture and stability of the complex RhCl(CO)(PH3)2, as well as its reactivity with H2 and CH4 molecules, were the subject of the Musaev and Morokuma s (MM) paper [16] performed at the MP2 level of theory with the double-zeta quality basis set and ECP for... 

The observation of C-H, Si-H, Si-I, and Si-Si bond activation by Pd(0) and Pt(0) complexes has prompted theoretical studies of Sakaki and coworkers [29] concerning the C-H, C-C, and Si-X (X = H, C, Si, and F) bond activation on the Pt(PH3)2 and Pd(PH3)2 complexes. In these calculations the MP2 and MP4(SDQ) methods with the double-zeta quality basis sets argumented by the polarization d function and ECP for heavier atoms have been used. As shown in Table III, the oxidative addition of C-H and C-C bonds to Pt(PH3)2 is endothermic by 6.5 and 5.2 kcal/mol, respectively, while it is exothermic by 25.6, 28.6, 14.1, and 46.4 kcal/mol for Si-H, Si-F, Si-C, and Si-Si bonds, respectively. These differences in exother-micity of the reaction have been explained in terms of the Pt-X bond energies metal-alkyl bonds are a few kilocalories per mole weaker than the metal-H bond, which in turn is 0-15 kcal/mol weaker than metal-silyl or metal-F bonds. The activation barriers increase via the trend SiH (0.7 kcal/ mol) < SiSi (17.0 kcal/mol) < SiF (26.8 kcal/mol) < SiC (28.1 kcal/mol)... 

The first article in the series of papers by Tatewaki and Huzinaga dealt with first-row transition metals (Sc-Zn). They reported two new minimal basis sets, originally called STD-SET(l) and DZC-SET(l), which yielded atomic orbital energies as good as, or better than, available double zeta quality basis sets. The same authors suggest procedures for splitting the valence shell AO so as to increase the basis set s flexibility. 

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