Vibrational spectra of difluorosilane from a hybrid ab-initio and DFT quartic force field

cited By 12International audienceFundamental frequencies of SiH2F2 and their isotopic shifts are computed using a hybrid quartic potential in which CCSD(T)/cc-pVTZ equilibrium values and harmonic wave-numbers are coupled to B3LYP/6-31+G** anharmonic terms in the framework of a variational treatment working in several spectral ranges. The mean-square deviation between our computed values and the most reliable experimental data are only 0.8% (SiH2F2) and 0.6% (SiD2F2). Calculation of both overtones and combination bands in the medium infrared region suggests a new assignment of some observed bands. © 2005 Elsevier B.V. All rights reserved

Performance of ab-initio and DFT PCM methods in calculating vibrational spectra in solution: formaldehyde in acetonitrile as a test case

cited By 31International audienceWe report the anharmonic spectra calculated for formaldehyde in acetonitrile solution using quartic force fields obtained at different levels of theory in connection with the SCI-PCM continuum solvent model. The fair agreement observed with the experimental data and with the observed shifts relative to the gas phase shows that the CCSD(T)/cc-pVQZ/SCIPCM and the hybrid CCSD(T)/cc-pVTZ//B3LYP/6-31+G(d,p)/SCIPCM approaches can be recommended to calculate reliable vibrational spectra in solution for medium size systems. © 2005 Elsevier B.V. All rights reserved

Vibrational computations beyond the harmonic approximation: performances of the B3LYP functional for semirigid molecules

The performances of the B3LYP density functional in the computation of harmonic and anharmonic frequencies were tested using 14 standard basis sets of double and triple zeta quality for a set of semirigid molecules containing from 4 to 12 atoms. The quality of the results is assessed by comparison with the most reliable computations available in the literature. The study reveals that the relatively cheap 6-31 +G(d,p) basis set performs a very good job for harmonic frequency calculations and that B3LYP anharmonicities are in close agreement with the reference values irrespective of the basis set used. On these grounds "hybrid force fields" are proposed to achieve the best compromise between computer time and quality of the results

Fast and accurate hybrid QM//MM approach for computing anharmonic corrections to vibrational frequencies

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