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Basis set and correlation energy dependence of geometry and harmonic frequencies of difluoroethane, CHF 2 CH 3
Author(s) -
Speis Martin,
Buss Volker
Publication year - 1992
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540130204
Subject(s) - anharmonicity , basis set , basis (linear algebra) , valence (chemistry) , harmonic , range (aeronautics) , normal coordinates , atomic physics , symmetry (geometry) , mathematics , geometry , physics , chemistry , computational chemistry , mathematical analysis , quantum mechanics , materials science , density functional theory , molecule , composite material
Optimum geometries and harmonic frequencies calculated at the Hartree–Fock and the MP2 level are reported for the fluorohydrocarbon CHF 2 CH 3 ; basis sets employed range from STO‐3G to 6‐311G**. The significantly shortened CC distance of 1.50 Å is reproduced already with the simplest split‐valence basis set; the CF distance of 1.36 Å on the other hand needs MP2 correction at least at the double‐ζ or 6‐311G* level. Symmetry coordinates defined in terms of internal coordinates are in qualitative agreement with available experimental evidence. Even the best basis set yields frequencies that differ from experimental (anharmonic) values by up to 200 cm −1 indicating the well‐known necessity of including higher‐order force constants if quantitative agreement with experiment is to be achieved.