The performance of the IMOMO and IMOHC integrated methods in predicting geometry, frequency and energy of reaction and activation in hydrogen abstraction reactions

Abstract

This paper compares how accurately two integrated methods (IMOMO and IMOHC) predict geometry, harmonic vibrational frequency and energy and enthalpy (0 K) changes (reaction and activation). These integrated methods split the “complete” system into two parts or layers, and apply different levels of theory to each, which is especially interesting for the treatment of large molecules. We located reactant, product and saddle point stationary points for seven hydrogen abstraction reactions, our test set, considering electronic and steric effects. In general, the two integrated methods behave similarly, reproduce the values of a benchmark calculation, correct the deficiencies of the low-level method description, and represent a substantial saving in computational cost. Their success is related to the higher-level description of the “model” system or inner layer, with the effect of the lower-level description of the outer layer being smaller.