Estimating the carbonyl anharmonic vibrational frequency from affordable harmonic frequency calculations

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 -