Stable points and transition states on the potential energy surface (PES) for sym-triazine (C3N3H3) have been calculated by using nonlocal density functional (NDFT) methods. Two decomposition mechanisms for sym-triazine are investigated. The first is a concerted triple dissociation of the sym-triazine ring to form the HCN products. Three-fold symmetry is maintained along the reaction path for this mechanism. The second is a stepwise decomposition mechanism involving the formation of an intermediate dimer species. The NDFT results, including structures, relative energies, harmonic vibrational frequencies, and corresponding eigenvectors, are compared with previously reported nb initio calculations. These results include critical points located and characterized through normal mode analyses at the MP2 level. QCISD(T) energy refinements of the MP2 critical points are used for the comparison of DFT predictions. Basis set size dependence is also examined. The nonlocal density functionals used are the exchange functional of Becke and the correlation energy functional of Perdew (BP86), Becke’s exchange and the correlation energy functional of Lee, Yang, and Parr (BLYP), Becke’s three-parameter hybrid exchange functional with the LYP correltation energy functional (B3LYP), and the Becke exchange with Perdew and Wang’s 1991 gradient-corrected correlation functional (BPW91). Basis sets used are 6-31G**, 6-311++G**, and cc-pVTZ. The reaction endothermicity predicted by B3LYP and BPW91 are in closer agreement with experiment than the QCISD(T) and MP2 predictions using the largest basis set. B3LYP predictions are within 1.1 kcal/mol of experiment. BPW91, BPSG, and BLYP frequencies agree most closely with experimental values for sym-triazine and HCN. DFT eigenvectors corresponding to vibrational modes for critical points on the PES compare well with MP2 predictions for most modes, indicating similarity in force fields and, therefore, atomic motion for the vibrations. Geometries predicted by all methods are in excellent agreement with experimental values for sym-triazine and HCN. All methods predict that the concerted triple-dissociation mechanism is the low-energy decomposition pathway for sym-triazine. DFT predictions of energies along the reaction path for the concerted triple-dissociation reaction are in qualitative agreement with MP2. All DFT methods predict structures of species along the reaction path that are in quantitative agreement with MP2 predictions.