Molecular structure and vibrational spectra of ibuprofen using density function theory calculations

The molecular geometry and the theoretical harmonic frequencies and infrared intensities of ibuprofen were calculated for all the molecules using five different density functional methods (mPW1PW91, B3PW91, B3LYP, HCTH and LSDA) with five basic sets, including 6-311G, 6-311++G, 6-311+G (d, p), 6-311++G (d, p) and 6-311++G (2d, 2p). The purpose of this research was to compare the performance of different DFT methods at different basis sets in predicting geometry and vibration spectrum of ibuprofen. The optimized geometric band lengths and bond angles obtained by using mPW1PW91 at 6-311++G (d, p) and 6-311++G (2d, 2p) basic sets show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of ibuprofen with calculated results indicates that the B3PW91/6-311++G (2d, 2p) level is superior to all the remaining levels for predicting all the vibration spectra on average for ibuprofen.

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► We investigated the molecular structure and vibrational spectra of ibuprofen by DFT.
► MPW1PW91 at 6-311++G (d, p) and 6-311++G (2d, 2p) afford the best quality to predict the structure of ibuprofen.
► B3PW91/6-311++G (2d, 2p) show better performance to predict the vibration spectra of ibuprofen.