TY - JOUR
T1 - Estimating the carbonyl anharmonic vibrational frequency from affordable harmonic frequency calculations
AU - Buczek, Aneta
AU - Kupka, Teobald
AU - Sauer, Stephan P. A.
AU - Broda, Malgorzata A.
PY - 2012/6
Y1 - 2012/6
N2 - A linear correlation between harmonic and anharmonic frequencies of water calculated at B3LYP level of theory was observed with a number of basis sets. Similar relationships were found in both the gas phase and solution for several small molecules. The best correlation was found for C=O stretch mode in formaldehyde, formamide and N-methylacetamide. The average difference between B3LYP harmonic and anharmonic v(C=O) frequencies calculated with several basis sets in these molecules was 30 cm-1. The ad hoc correction of -30 cm-1, added to harmonic frequencies of two different carbonyl groups present in a structure of a larger molecule was tested as a fast way of predicting anharmonic frequencies without elaborated calculations. The proposed approach was tested successfully on a larger molecule of E and Z isomers of N-acetyl-α,β-dehydrophenylalanine N',N'-dimethylamide [Ac-(E/Z)-ΔPhe-NMe2] and the estimated anharmonic v(C=O) frequencies were close to directly calculated results.
AB - A linear correlation between harmonic and anharmonic frequencies of water calculated at B3LYP level of theory was observed with a number of basis sets. Similar relationships were found in both the gas phase and solution for several small molecules. The best correlation was found for C=O stretch mode in formaldehyde, formamide and N-methylacetamide. The average difference between B3LYP harmonic and anharmonic v(C=O) frequencies calculated with several basis sets in these molecules was 30 cm-1. The ad hoc correction of -30 cm-1, added to harmonic frequencies of two different carbonyl groups present in a structure of a larger molecule was tested as a fast way of predicting anharmonic frequencies without elaborated calculations. The proposed approach was tested successfully on a larger molecule of E and Z isomers of N-acetyl-α,β-dehydrophenylalanine N',N'-dimethylamide [Ac-(E/Z)-ΔPhe-NMe2] and the estimated anharmonic v(C=O) frequencies were close to directly calculated results.
KW - Faculty of Science
KW - harmonic frequency
KW - anharmonic frequency
KW - Quantum Chemistry
KW - Computational Chemistry
KW - Vibrational Spectroscopy
U2 - 10.1007/s00894-011-1262-6
DO - 10.1007/s00894-011-1262-6
M3 - Journal article
SN - 1610-2940
VL - 18
SP - 2471
EP - 2478
JO - Journal of Molecular Modeling
JF - Journal of Molecular Modeling
IS - 6
ER -