Extrapolation of water and formaldehyde harmonic and anharmonic frequencies to the B3LYP/CBS limit using polarization consistent basis sets

Abstract

The harmonic and anharmonic frequencies of fundamental vibrations in formaldehyde and water were successfully estimated using the B3LYP Kohn-Sham limit. The results obtained with polarization- and correlation-consistent basis sets were fitted with a two-parameter formula. Anharmonic corrections were obtained by a second order perturbation treatment (PT2). We compared the performance of the PT2 scheme on the two title molecules using SCF, MP2 and DFT (BLYP, B3LYP, PBE and B3PW91 functionals) methods combined with polarization consistent pc-n (n = 0, 1, 2, 3, 4) basis sets, Dunning’s basis sets (aug)-cc-pVXZ where X = D, T, Q, 5, 6 and Pople’s basis sets up to 6-311++G(3df,2pd). The influence of SCF convergence level and density grid size on the root mean square of harmonic and anharmonic frequency deviations from experimental values was tested. The wavenumber of formaldehyde CH2 anharmonic asymmetric stretching mode is very sensitive to grid size for large basis sets; this effect is not observed for harmonic modes. BLYP-calculated anharmonic frequencies consistently underestimate observed wavenumbers. On the basis of formaldehyde anharmonic frequencies, we show that increasing the Pople basis set size does not always lead to improved agreement between anharmonic frequencies and experimental values.FigureSensitivity of water B3LYP calculated harmonic and anharmonic vs(OH) frequencies on selected Pople and polarization consistent basis sets size. The results for pc-n basis sets were fitted with two parameter formula and the CBS(2,3,4) estimatedElectronic supplementary materialThe online version of this article (doi:10.1007/s00894-010-0913-3) contains supplementary material, which is available to authorized users.

Estimating the carbonyl anharmonic vibrational frequency from affordable harmonic frequency calculations

“…On the other hand, it is necessary to point out that a simple harmonic frequency scaling (with the factor 0.9686 from [4]) leads to significantly better agreement with experimental frequencies than the result from VPT2 calculations (average deviation from experimental values of harmonic vs scaled harmonic is 59.0 and 4.8 cm −1 ). Similar better performance of simple harmonic frequency scaling than VPT2 predicted anharmonicity corrections in the analysis of experimental IR/Raman spectra was also noted in our recent studies [30,31]. However, the drawback of using scaling factors is their limited availability, which is restricted to a narrow range of methods and basis sets, and the lack of a rigorous theoretical background.…”

“…The results of our recent studies on anharmonicity of vibration modes in water, formaldehyde [30] and formamide [31] prompted us to compare our harmonic and anharmonic frequencies with experimental values and led to an evaluation of the performance of both types of calculations. In addition, some dependencies between these individual types of frequencies were left without analysis.…”

Theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis-, and trans-1,2-difluoroethylenes

“…The BLYP was selected to check its feasibility of predicting harmonic frequencies involving C-F vibrations closer to experiment than other density functionals. 50,51 Selection of such large and flexible basis set, additionally augmented with diffuse functions, should produce results similar to obtained with Dunning's type aug-cc-pVDZ, and sometimes aug-cc-pVTZ basis sets. [43][44][45][46][47] On the other hand, this basis set is significantly smaller than aug-cc-pVTZ or pc-3.…”

“…42 On the other hand, B3LYP overestimates the harmonic frequencies by 3%-5% and the predicted values are often scaled before comparison with experiment. 48,49 To avoid this empirical approach we will use the BLYP density functional which provides significantly lower harmonic frequencies 42 (see also our earlier studies 50,51 ). Besides, we will use the second order vibrational perturbation theory [52][53][54] (VPT2) to obtain B3LYP anharmonic frequencies.…”

Theoretical prediction of structural, vibrational and NMR parameters of plastic optical fiber (POF) material precursors. Cis and trans perhydro- and perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolanes

“…The use of anharmonic model [44][45][46] is significantly more expensive computationally and the selection of a functional which is capable of producing wavenumbers closer to experiment (e. g. without resorting to anharmonic model) is another option. From our earlier vibrational studies on several small molecules we noticed that BLYP produces results significantly closer to experiment [47][48][49].…”