Vibrational frequencies calculations, methods

All of the theoretical methods that allow for geometry optimization predict the bowl-shaped conformation of 8 to predominate over the planar alternative. However, the calculated energy differences between the two conformations differ drastically and span the range of 0.8 to 84 kcal/mol. Moreover, the calculated energy difference between the plants and bowl-shaped conformers is quite important since it represents the barrier for bowl-to-bowl inversion if (a) planar corannulene represents the transition state (TS) for the process, and (b) the entropic term in AG is negligible. Condition (a) seems to be fulfilled, since vibrational frequency calculations give one and only one imaginary frequency for the planar structure... 

Calculated interaction energies (corrected for the basis set superposition error and ZPE) are relatively large and amount to 9.8 kcal mol-1 by B3LYP and 8.9 kcal mol-1 by CCSD(T) methods. Harmonic vibration frequencies calculated for monomers and the complex are in reasonable agreement with experimental data241. Agreement is good for IR band shifts due to complexation and isotopic substitution. 

Table 4.10. The Si-O bond lengths (R(Si-O)] and vibrational frequencies calculated" using Hartree-Fock-Roothaan (SCF) molecular-orbital methods with different basis sets and compared with experimental properties of Si(OH)4 in Dj, symmetry...

Note that a vibrational-frequency calculation must be preceded by a geometry optimization using the same method and basis set as used for the frequency calcula-... 

Harmonic vibrational frequencies calculated by the Hartree-Fock method are... 

K. Wiberg et al., J. Phys. Chem., 99,9072 (1995)], but other workers recommend other values [C.-G. Zhan and D. M. Chipman, J. Chem. Phys, 109,10543 (1998)]. Since the solute s electronic wave function changes in each SCRF iteration, the size of the molecular cavity changes in each IPCM iteration. In the IPCM method, is calculated from apparent surface charges. The self-consistmt isodensity PCM (SCIPCM) method is a refinement of the IPCM method Foresman and Frisch, Chapter 10), which allows geometry optimization and vibrational-frequency calculations to be done for the solute molecule in solution. 

To understand the stereoselectivity of this reaction, DFT [5, 6] studies have been performed with GAUSS1AN03 program [7] using B3LYP [8, 9] method. For C, H, O, 6-311+G basis set was used for Zr, Lanl2DZ basis set with ECP [10] was used. Harmonic vibration frequency calculation was carried out and the optimized structures are all shown to be transition states with one imaginaiy frequency. In the calculation models, = Me, and R = Ph. The results are shown in Fig. 3. 

Biczysko M, Panek P, Scalmani G, Bloino J, Barone V (2010) Harmonic and anharmonic vibrational frequency calculations with the double-hybrid b2plyp method analytic second derivatives and benchmark studies. J Chem Theory Comput 6 2115-2125. doi 10.1021/ctl00212p... 

It is well known that the harmonic vibrational frequencies calculated by DFT methods are usually systematically overestimated with respect to experimental fundamentals, which was the case for most of our results, too. This systematic overestimation used to be corrected by rescahng the spectrum using scaling factors that are well tuned to specific functionals and basis sets. Such factors are available, e.g., for B3LYP/6-311G [56]. For our schemes with... 

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