Improved interpolated correction schemes for dual-level direct dynamics calculation

A set of new correction schemes for dual-level variational transition-state theory calculation has been developed. In the new schemes, an intermediate level of theory is employed to better estimate the width of the reaction e nergy barrier. Then, adjustable parameters are set in the final calculation to reproduce the estimated high-level barrier width in addition to the hig h-level energy of reaction and barrier height. The new schemes have been te sted in the rate constant calculation of H + H2S -> HS + H-2 and OH + CH4 - > H2O + CH3 reactions with potential energy surface information obtained fr om several low- and high-level ab initio theories. Compared to the previous correction schemes, the dual-level calculation based on the new schemes pr oduced results, in most cases, in significantly better agreement with the r eference high-level calculation. The new schemes are expected to predict mo re accurate rate constants for those reactions in which tunneling effects a re important.