At the HSE/6-31G level of theory, the C1 configuration is energetically preferable with relative energies of C2 and C3 configurations equal to 1.104 and 13.969 kcal/mol, respectively (Table 3). The energy difference value is found much higher the temperature factor for C2 (7029.5K) and proportional for C3 (555.5K), which limits rotation of iron porphyrin on top of AGNR without external optical excitation.