Theoretical comparative study on two C20H16 and three C28H20 isomers in which the hexaprismane cages are parallel or perpendicular

Quantum-chemical calculations on two C20H16 isomers and three C28H20 isomers in which the hexaprismane cages are parallel or perpendicular have been performed using density functional theory (DFT) method. The geometric structures, energies, vibrational frequencies, and vertical ionization energy as well as vertical electron affinity of various isomers have been obtained at the B3LYP/6-31G∗∗ level of theory. Meanwhile, the present paper has also computed the enthalpies of formation for different isomers so as to evaluate their stability from a thermodynamic point of view. It has been concluded that the isomer in which the hexaprismane cages are perpendicular is more stable and has smaller heat of formation.