Ab initio, DFT calculation and vibrational analysis of 2,4,6-trinitrotoluene

Raman intensities and frequencies of 2,4,6-trinitrotoluene have been calculated using B3LYP/6-31+G**, 6-311+G** and Sadlej’s medium-sized polarized basis sets (Sadlej pVTZ). Transitions in the 700–3400cm−1 region were assigned. These assignments were facilitated by performing a normal mode analysis using a combination of localized and delocalized coordinates. Comparisons of the uniform scaled frequencies with the experimentally available results showed an average absolute deviation of 14cm−1. The relative Raman intensities calculated using 6-311+G** and Sadlej pVTZ polarized basis sets were found to be in very good agreement with the experimentally measured Raman intensities. One of the major advantages of using these basis sets is the removal of degeneracies found for the C–H stretching, C–H in-plane bending, ring breathing and methyl deformation modes, when 6-31+G** and 6-311+G** basis are used. The removal of these degeneracies clearly shows an improvement in the agreement between calculated and experimental frequencies. The geometry of 2,4,6-trinitrotoluene was calculated at B3LYP/6-31+G**, 6-311+G**, Sadlej pVTZ and MP2/6-31G* methods. Two lower energy structures A and B were computed and the global minimum structure was found to be the structure A in both methods.