Double zeta plus polarization -quality basis sets

Calculation has been performed mainly at the HF level with the double-zeta plus polarization quality basis sets and ECP for Pd, P, Si, and Sn. The energetics for R = Me has been recalculated at the MPn (n = 2-4) level at the HF geometries. The overall reactions for various RCCH (R = CN, H, CH3, and OCH3) and H3SiSnH3 with the model catalyst Pd(PH3)2 have been studied. It has been shown that H3Si-SnH3 easily, with a few kilocalories per mole barrier, adds oxidatively to the catalyst Pd(PH3)2 and the resultant complex lies only 5.9 kcal/mol lower than the reactants. The next step, acetylene coordination to the catalyst, causes with the dissociation of... 

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... 

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. 

The components -0.41, +0.61, and -0.19 follow from ab initio SCF-MO calculations with a basis set of double zeta plus polarization quality [18]. Further values were calculated with a minimal [9] and a double zeta basis [16]. Two semiempirical methods [34,35] were also employed [33]. 

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. 

More recent ab initio calculations on the formation of the adduct H3P BH3 applied basis sets of double zeta [95], double zeta plus polarization [96], and 4-31G quality (including counterpoise corrections) [97]. A slightly exothermal decomposition of the adduct is predicted at the CEPA level and agrees with the observed instability of the adduct in the gas phase at ambient temperature [96]. A recent ab intio MO calculation for the 1 1 adduct H3P - BF3 at the SCF and MP2 levels with basis sets of triple zeta quality gave a very large P-B distance. The adduct can thus be considered only a weak van der Waals complex which should not easily be observable in experiments. The calculated results therefore disagree [98] with the alleged experimental observation of this adduct in the gas phase [99]. 

Full configuration interaction (FCI) by definition gives the exact n-particle energy within the given basis set. (Since it is the exact solution, this happens irrespective of the quality of the zero-order wave function.) Because its computational requirements ascend factorially with the size of the system, application to practical systems using one-particle basis sets of useful size will be essentially impossible for the foreseeable future. Even using the fastest available computational hardware and parallelized codes, an FCI calculation on H2O in a double-zeta plus polarization basis set is about the state of the art at present. ... 

The calculations shown in this work have been performed using the Amsterdam Density Functional (ADF) code [20,21]. All of them are spin not polarized. The influence of the quality of the basis set on the Re value has been explored taking as a guide the case of Mn in fluoroperovskites. For this goal two types of basis sets have been employed. Firstly calculations have been carried out by means of functions of quality IV (which are implemented in the ADF code) involving triple zeta basis functions plus a polarization function. In a second step Re has also been computed using double zeta functions of quality II for F and ions. 

For most molecules studied, modest Hartree-Fock calculations yield remarkably accurate barriers that allow confident prediction of the lowest energy conformer in the S0 and D0 states. The simplest level of theory that predicts barriers in good agreement with experiment is HF/6-31G for the closed-shell S0 state (Hartree-Fock theory) and UHF/6-31G for the open-shell D0 state (unrestricted Hartree-Fock theory). The 6-31G basis set has double-zeta quality, with split valence plus d-type polarization on heavy atoms. This is quite modest by current standards. Nevertheless, such calculations reproduce experimental barrier heights within 10%. 

X =-16.82, Xaa = 20.91, Xbb = 17.50, and Xcc = 12.06 were calculated [28] by solving the coupled Hartree-Fock equations in terms of localized MOs, each with an optimum gauge origin (see [29, 30]). The diamagnetic susceptibilities from an ab initio calculation with a contracted Gaussian basis set of double zeta quality plus polarization functions, Xaa = 43.53, Xbb = 119-40, x c = 136.90, agree quite well with the values tabulated above [2]. 

Taking the opposite view, Szalewicz et al. examined the water dimer with still larger basis sets involving 212 (s,p,d,f) functions. They found that the SCF interaction energy could be satisfactorily reproduced with a small double-zeta quality basis plus properly chosen polarization functions, when used in conjunction with the counterpoise method. The correlation contribution to the interaaion energy was computed to be -1.0 0.3 kcal/mol. Alberts et al. have also recently advocated the use of the full counterpoise method for weakly bound complexes of HF and CO, CO2 and N2CO. 

To illustrate how well DFT or ab initio methods predict the dipole moments. Table 1 illustrates the comparison between theory and experiment for eight small molecules. The error statistics are summarized in Table 2. In general, the quality of the basis set plays an important role in the prediction of dipole moments. We see that the 6-3IG basis set provides poor predictions, even when applied with a QCISD level of theory. The performances of the double-zeta basis set plus polarization functions (6-3IG, DZVPD (double-zeta valence orbitals plus polarization and diffuse functions on heavy atoms), and cc-pVDZ (correlation-consistent polarized valence double-zeta)) are poorer than those from the polarized triple-zeta basis sets. The only exception is B-P/DZVPD (B-P = Becke-Perdew), from which we obtained an average absolute deviation of 0.040 debye, lower than that (0.053 debye) from B-P/TZVPD (triple-zeta valence orbitals plus polarization and diffuse functions on heavy atoms). It can be seen that the inclusion of correlation effects through either ab initio or DFT approaches significantly improves the agreement. 

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