TZVP basis set

All electron calculations were carried out with the DFT program suite Turbomole (152,153). The clusters were treated as open-shell systems in the unrestricted Kohn-Sham framework. For the calculations we used the Becke-Perdew exchange-correlation functional dubbed BP86 (154,155) and the hybrid B3LYP functional (156,157). For BP86 we invoked the resolution-of-the-iden-tity (RI) approximation as implemented in Turbomole. For all atoms included in our models we employed Ahlrichs valence triple-C TZVP basis set with polarization functions on all atoms (158). If not noted otherwise, initial guess orbitals were obtained by extended Hiickel theory. Local spin analyses were performed with our local Turbomole version, where either Lowdin (131) or Mulliken (132) pseudo-projection operators were employed. Broken-symmetry determinants were obtained with our restrained optimization tool (136). Pictures of molecular structures were created with Pymol (159). 

Cyclic voltammetry, kinetic studies, and DFT calculations using a BP functional and the TZVP basis set showed that the major pathway of the non-regiospeciflc zinc-reduced titanocene-mediated ring opening of epoxides was initiated by a titanium dimer-epoxide compound that reacted in a rate-determining electron transfer mechanism 25 The calculations showed that the transition state is early so the stereoselectivity is determined by steric effects rather than by the stability of intermediate radicals. This was confirmed by studies with more sterically crowded catalysts. 

On the basis of these results and in the absence of experimental data the choice of the best basis set is not an easy task. Therefore, as a compromise between reliability and reasonable computational cost we have employed mainly the 6-31G and TZVP basis sets in the hybrid and gradient-corrected computations, respectively. 

Fig. 4. Curve of rotation of trares-diazene coordinated in complex 1(N2H2) using the BP86/RI (left) and B3LYP (right) methods (TZVP basis set). The zero point of rotational energy is fixed arbitrarily. Note that the hydrogen atoms are not aligned with the S-Fe-S axes since they always point into the direction of the sulfurs lone pairs.

The results from the nonlocal and hybrid DFT calculations show trends similar to those observed for the MO calculations. The computed geometries are very similar to each other the calculated bond lengths for the breaking bond range from 2.14 A, calculated by the hybrid adiabatic connection method (ACM) [24], to 2.16 A, calculated by the nonlocal BLYP [25, 26] functional. A comparison of the results from the nonlocal Becke-Perdew [27] calculations using DZVP and a TZVP basis sets shows that the geometries are influenced to a very small extent by basis set effects [12]. The activation energies calculated by the different nonlocal methods are too low by 1-3 kcal/mol, whereas the hybrid DFT methods overestimate Ea by approximately the same amount. Both the nonlocal and the hybrid DFT methods tend to overestimate the heat of reaction by up to 7 kcal/mol, calculated by the ACM/6-31G method. 

Similar performance tests have been carried out using the GAPW method for both the pseudo potential and the all electrons implementation. For these methods, the TZV2P and the TZVP basis sets have been employed respectively. The smaller basis set used for the all electron calculations is due to memory constraints. We ran single point energy calculations on an IBM Regatta node (32 CPUs) with a plane wave cutoff of 200 Ry and the BLYP functional. As expected, also in this case by increasing the size of the box from 32 up to 1024 (512 for the all electron case) water molecules, the cpu... 

In order to assess several levels of theory, the first smdy was performed on the prototypical system SiH4 + C2H4, using T1H2 as catalyst (46). These calculations were performed using the TZVP basis set, at the Hartree-Fock, MP2, and CCSD(T) levels of theory. It is very clear from a detailed analysis of the reaction path that correlation corrections are essential to obtain a reliable prediction of... 

Calculations of the full manifold of the electronic states spanned by these configurations have been done on structures obtained from DFT geometry optimizations using the Perdew-Becke-Ernzerhof (PBE) functional [119, 120], empirical van der Waals corrections [121] for the DFT energy, the scalar relativistic zero-order regular approximation (ZORA) [122], and the scalar relativistically recontracted (SARC) [123] version of the def2-TZVP basis set [124]. 

The benchmark indicates that the PA of ammonia is very well reproduced employing the 6-311-m-G or the TZVP basis sets coupled with B3LYP, PWP and BP exchange-correlation potentials. For this reason, the PA and GPB of other further compounds reported in Tables 3-5 are calculated at these levels of theory. 

If the TZVP basis set is u.sed in connection with hybrid potentials, the value... 

Considering that the experimental uncertainty is of 2 kcal/mol, almost all our results seem to be reliable as well as those obtained with GVB 1104 and G2 116 procedures. A good convergence is reached already with the TZVP basis set. The importance of this result lies in the possibility to compute GPA for larger system with acceptable computer efforts. 

The calculations performed for acetic and propanoic acids (see Table 8) confirm the opportunity to use the medium-sized TZVP basis set to obtain good results. On the other hand the lack of other theoretical data regarding the propanoic acid reflects the difficulty to treat, with expensive procedures, such a kind of system. 

For the polyad studies described below the hybrid type DFT calculations with the Becke 3 term and the Lee, Yang and Parr exchange functional and also the BLYP method have been used. In addition to the standard gaussian-type basis sets such as 6-31G(d) or 6-311G(d,p) die DZVP and TZVP basis sets optimized for DFT calculations have also been applied. Finally, for polyad complexes with metal ions pseudo potentials have been adopted. ... 

The selected conformations are subjected to full geometry optimization at RI-DFT level of theory [40-42], using the Becke-Perdew combination of functionals [43 4] and Ahlrichs s TZVP basis sets [45]. Solvent effects are estimated using COSMO [46] with dielectric constants of 4.0, simulating the interior of an enzyme. 

Ab initio calculations of S nuclear quadrupole coupling constants have been carried out on a variety of sulfur compounds using a TZVP basis set <92ZN(A)203>. The equilibrium geometric parameters calculated by this method follows the trend of the other ab initio methods and the values are within the acceptable limits. 

DFT calculations for the [(P)Fe]2( -N202) model complex using B3LYP functional with TZVP basis set was employed to confirm the structure of [(0EP)Fe]2(/M-N202) (254). We note that the calculations predicted an energy gap of 2 kcal moP between the trans-N2O2 product and the ris-N202 product, an indication that both isomers may form. 

In order to elucidate the bonding situation for molecular SiS and GeS ab initio calculations have been performed in which electron correlation has been involved (MP2 and DFT) [3, 4], The results (energy, atomic distances) of the MP2 calculations are summarized in Table 2. Afterwards population analysis and frequency calculations have been performed. Comparing the latter with the experimental data demonstrates that MP2 calculations with TZVP basis sets give the best fit. Therefore only these theoretical results are listed in Table 1. 

The geometry file is the input information for the following quantum chemical calculation, as shown in Figure 9.6. The software Turbomole [15, 16] is used for the density functional theory (DFT) calculation with COSMO boundary condition (i.e., the dielectric constant e = oo). The software needs some additional input information. The exchange functional from Becke [17-19], the correlation functional from Perdew et al. [20, 21], and the TZVP basis set [22, 23] are specified. The COSMOtherm-optimized atomic radii are used [24]. The result of the COSMO... 

For large molecules where the use of diffuse augmentation is prohibitive, an alternative is to use triple-zeta valence (TZV) basis sets. The TZVP (def-2-TZVP ° ) basis set corresponds to [Ssipldlf] on C and [3slp] on FI. It also includes a second set of polarization functions on nonhydrogen atoms and provides a description of the valence electrons that is... 

By adding a s p d f] set of diffuse functions to TZVP, we obtain the aug-TZVP basis set. The aug-TZVP excitation energies of all states of naphthalene, except the 1 Rydberg state, are within 0.01 eV of the reference aug-QZVP results and can be considered essentially converged. A similar observation can be made for the oscillator strengths in Table 3. 

As an illustration of the performance of TDDFT, we compare various density functionals and wave function methods for the first singlet excited states of naphthalene in Tables 4, 5, and 6. All calculations were performed using the aug-TZVP basis set, while the complete active space self-consistent field (SCF) with second-order perturbation theory (CASPT2) results from Ref. 200 were obtained in a smaller double-zeta valence basis set with some diffuse augmentation. The experimental results correspond to band maxima from gas-phase experiments however, the position of the band maximum does not necessarily coincide with the vertical excitation energy, especially if... 

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