Double zeta plus polarization

Although there is no strict relationship between the basis sets developed for, and used in, conventional ah initio calculations and those applicable in DFT, the basis sets employed in molecular DFT calculations are usually the same or highly similar to those. For most practical purposes, a standard valence double-zeta plus polarization basis set (e.g. the Pople basis set 6-31G(d,p) [29] and similar) provides sufficiently accurate geometries and energetics when employed in combination with one of the more accurate functionals (B3LYP, PBEO, PW91). A somewhat sweeping statement is that the accuracy usually lies mid-way between that of M P2 and that of the CCSD(T) or G2 conventional wave-function methods. 

Comparison of the experimental potential in a crystal and the theoretical potential for an isolated molecule is an excellent test for the transferability of theoretical isolated molecule densities to problems such as molecular packing and protein folding. A systematic study of this kind was done on L-alanine. Figure 8.3 shows a comparison between theory and experiment for a plane containing the C—N bond in this molecule. The comparison is with the 6-3IG basis set of double-zeta-plus-polarization quality. The agreement of experiment with more modest basis-set calculations was found to be inferior, which gives confidence in the experimental results. Both in the plane shown, and in the plane of the carboxyl... 

Table 2.2. A double-zeta plus polarization (DZP) basis forH2 calculations.

The number of basis functions (defined by the chosen basis sets) used to construct the molecular orbitals also strongly affects the effort/accuracy ratio. The use of minimal basis sets yielded wrong results (56), whereas reasonable agreement with experiment is obtained when double zeta plus polarization basis sets are applied. Correlated methods require larger basis sets to include as much electron correlation as possible. This implies that in addition to the increased computational demand of such methods, a further increase of the computational cost results due to the requirement of using larger basis sets. 

The basis set consisted of two Is, two 2s, two sets of 2p and one set (five components) of 3d real Slater-type basis functions (STFs) on boron, two Is and one set of 2p STFs on each hydrogen. It was thus of double-zeta plus polarization quality. The z axis was taken to be perpendicular to the plane of the nuclei. 

In the ah initio case, the relevant finite-dimensional one-electron space is spanned by a minimum, double-zeta, double-zeta plus polarization, etc., basis set and further approxi-... 

Figure 5.1 A double zeta basis allows for different bonding in different directions 1 DZ basis forms a Double Zeta plus Polarization (DZP) type basis. There is a variation where polarization functions are only added to non-hydrogen atoms. This does not mean that polarization functions are not important on hydrogens. However, hydrogens often have a passive role, sitting at the end of bond which does not take an active part in the property of interest. The errors introduced by not including hydrogen polarization functions are often rather constant and, as the interest is usually in energy differences.

Distribution functions in simulations, 378 Double Zeta plus Polarization (DZP) basis set, 153... 

B3LYP Three-parameter hybrid density functional method the MCPF method is an extension of the singles and doubles configuration interaction approach D95- " - is a Dunning double-zeta plus polarization and diffuse functions quality basis set D95 is the D95- " - basis set in which basis set functions and the polarization functions on the hydrogen atoms have not been included. 

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