Characterization of the Temporary Anion States on Perfluoroalkanes via Stabilized Koopmans' Theorem in Long-Range Corrected Density Functional Theory

The stabilized Koopmans' theorem (SKT) in long-range corrected density functional theory is used to characterize the temporary anion states of perfluoro-n-alkanes (n-PFAs) from C-2 to C-5, and perfluorocycloalkanes (c-PFAs) from C-3 to C-4. In this approach, stabilization is accomplished by varying the exponents of appropriate diffuse functions. The energies of temporary anion states are then identified by investigating the relationship between the resultant eigenvalues and scale parameter. The characteristics of resonance orbitals are also examined. For the lowest unfilled orbitals of perfluoroalkanes, results indicate that they are mainly from the pi-bonding interactions between all neighboring C atoms. In addition, their energies decrease as the sizes of the perfluoroalkanes increase. Moreover, the energies of the c-C3F6/c-C4F8 are lower than those of the corresponding n-C3F8/n-C4F10. When compared with experimental data, our SKT calculations can yield conformable results. Thus, this SKT approach can provide more information on the resonance states of perfluoroalkanes.