Quantum-chemical calculations of physicochemical properties of high enthalpy 1,2,3,4- and 1,2,4,5-tetrazines annelated with polynitroderivatives of pyrrole and pyrazole. Comparison of different calculation methods

•Physicochemical properties of 1,2,3,4- and 1,2,4,5-tetrazines have been calculated.•Quantum-chemical methods of various levels have been comparatively assessed.•Different approaches for calculating the enthalpy of formation have been used.•Compounds under study can be effective components of energy-intensive compositions.