THE VIBRATIONAL FREQUENCIES OF FULLERENES FROM AN UPDATED QCFF PI HAMILTONIAN/

The vibrational force fields of the two most abundant fullerenes, C-60 and C-70), are computed with a version of the quantum consistent forc e field for pi electrons (QCFF/PI) Hamiltonian in which the parameter used to mimic the a-electron potential due to CCC bond angles of conju gated carbon frameworks is modified. It is shown that the single param eter change leads to CCC force constants close to the scaled ab initio force held values and reduces considerably the discrepancies between computed and observed vibrational frequencies of unsaturated hydrocarb ons. Applied to buckminsterfullerene, it reduces the average deviation of computed vibrational frequencies from 55 cm(-1) to 31 cm(-1) and b rings the accuracy of QCFF/PI close to the best first principles calcu lations available to date for C-60,C- at a fraction of the cost. The n ew set of computed C-70 vibrational frequencies is presented and an up dated assignment of the experimentally available vibrational data is p roposed.