MOLVIB vs VEDA. Revealing the best program to generate safe and reliable vibrational analysis

In this investigation, complete assignments performed with the MOLVIB program for the two Cis and Trans conformers of 4-Chloro-3-fluorobenzaldehyde optimized at the B3LYP/6–311+G(3df,p) level of theory, the two 4-Amino-3-(4- hydroxybenzyl)-1H-1,2,4-triazole-5(4H)-thione and thiol tautomers by using B3LYP/6–31+G(d,p), Phomarin by using B3LYP/6–311++G(d,p) and finally, Rabeprazole by using B3LYP/6–31G(d,p) have been compared with the reported for the same compounds with the VEDA program at the same levels of theory. The results evidence that both programs are suitable to perform very good harmonic force fields, however, the atoms numbering, the knowledge of all expected vibration modes for the compound and the correct definitions of the normal internal coordinates are necessary requirements to obtain correct and reliable assignments of the normal vibration modes of species. Hence, only a researcher with expertise in vibrational analysis can generate reliable and secure assignments suitable for identifying a species using the infrared and Raman spectra. Important errors and serious omissions reported in the previous assignments for those compounds with VEDA have been here corrected and supplemented with the more exact harmonic force fields obtained with MOLVIB. Furthermore, the scaled harmonic force constants of studied species have been updated for all compounds for the first time.