Anharmonic force fields of perchloric acid, HClO4, and perchloric anhydride, Cl2O7. An extreme case of inner polarization

DFT (density functional theory) anharmonic force fields with basis sets near the Kohn–Sham limit have been obtained for perchloric acid, HClO4, and perchloric anhydride, Cl2O7. Calculated fundamental frequencies are in very good agreement with available experimental data. Some reassignments in the vibrational spectra of Cl2O7 are proposed based on our calculations. HClO4 and Cl2O7 are particularly severe examples of the ‘inner polarization’ phenomenon. The polarization consistent basis sets pc-1 and pc-2 (as well as their augmented counterparts) should be supplemented with two (preferably three) and one (preferably two) high-exponent d functions, respectively, on second-row atoms. Complete anharmonic force fields are available as electronic supporting information [1].