Mixed basis set

Slovenia), using the DFT implementation in the Gaussian03 code. Revision C.02 (8). The orbitals were described by a mixed basis set. A fully uncontracted basis set from LANL2DZ was used for the valence electrons of Re (9), augmented by two / functions Q =1.14 and 0.40) in the full optimization. Re core electrons were treated by the Hay-Wadt relativistic effective core potential (ECP) given by the standard LANL2 parameter set (electron-electron and nucleus-electron). The 6-3IG basis set was used to describe the rest of the system. The B3PW91 density functional was used in all calculations. 

To compare with the experimental NMR data, the 13C isotropic chemical shifts of all of the acetylide and vinylidene complexes were calculated. These systems were too large for us to be able to do chemical shift calculations at the MP2 level. We thus used the GIAO method at the RHF level. Fortunately, the RHF level of theory appears to be adequate for these complexes. We used a mixed basis set for the GIAO, with tzplarge+ on C, tzplarge on H, tzp on the Mg and O associated with the adsorbed species, and dzp on the remaining Mg and O (26). 

An interesting mixed-basis-set method for use in SCF calculations has been described by Billingsley and Trindle,52 with application to LiC>2. One-centre and most two-centre integrals are evaluated analytically, whilst less tractable integrals are approximated by a gaussian expansion of the STO s. Examination of portions of the... 

Another aspect ol basis set balance is the occasional use of mixed basis sets, tor me optinuzation ot oasis lunction exponents ts an example or a nigniy non-imear... 

Level shitting, for achieving SCt convergence. Mixed basis sets, 134 Population Analysis, 2l7 ... 

As previously mentioned in section 4-2, Linnett and Bacsky in 1972 used a mixed basis set to improve the results of total energy. In 1999 J. E. Perez et alP has applied 1 s Gaussian and 1 s Slater types in an SCF calculation on LiFI in order to improve the results. Table 23 is the presentation for comparison the different results. 

Calculations at the SCF/(mixed basis set) level suggest the tautomerization barrier between the dimers to be 10.7-14.3 kcal/mol, which is about three times smaller than the potential energy barrier for a single proton transfer in monomers (84CPL(107)330, 94JST(312)157). The presence of the dimers of 2-hydroxypyridine in the gas phase was confirmed by IR spectra (01SA(A)2659). 

The time-dependent Schrodinger equation for the effect of the collision dynamics on the probability amplitudes for being in S, T, and T is most conveniently represented in the mixed state basis (3.3), as this makes all coupling matrix elements vanish in the limit of infinite molecule-perturber separations. Within the mixed basis set, the matrix elements of V can be worked out to give... 

However, caution is needed in the use of mixed or spliced basis sets. It is possible that the use of disparate basis set qualities for different regions of an organometallic may engender an imbalance in the basis set leading to a Robin Hood scenario. Those portions that are poor in basis set can rob basis functions from those rich in basis sets, particularly if the imbalance is great. This scenario is also particularly problematic for those atoms with mixed basis sets that are in proximity to each other, that is, at the interface region. Additionally, diffuse (small exponent, large in radial extent) basis functions are particularly prone to thievery by atoms with small basis sets. 

Except for very small systems, it is impractical to saturate the basis set such that the absolute error in the energy is reduced below chemical accuracy, say 4kJ/mol. The important point in choosing a balanced basis set is to keep the error as constant as possible. The use of mixed basis sets should therefore only be done after careful consideration. Furthermore, the use of small basis sets for systems containing elements with substantially different numbers of valence electrons (such as LiF) may produce artefacts. 

Miyoshi and co-workers carried out several studies related to adsorption. In an early study they modeled adsorption of SO2 on Ni(lll) and Cu(lll) surfaces [240] using a hybrid DFT functional and a mixed basis set (ECP [241] and cc-pVDZ [112]), followed by single-point energy evaluations at the CASSCF level with MCPs. For structural studies, Ni4S02 and Q14SO2 were chosen as model clusters to represent SO2 adsorbed on the metal M(lll) surfaces. Single-point... 

Figure 2.41 Partition schemes with three different sizes of the upper layer (s small, m medium, and i iarge) for the shieiding calculations using the mixed basis set and ONIOM methods. For the medium-sized partition, the mixed basis set scheme does not include four alpha hydrogen atoms in the upper layer. Reprinted from Ref. [188] Copyright 2006...

Mixed basis sets, 154 MM2, MM3, MM4 force fields, 40 MMFF force field, 40 MMP2, MMP3 method, 27 MNDO/d method, 89 MNDOC method, 87... 

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