Performance of Density Functional Theory on the Potential-Energy Surface of the H + OCS System

Abstract

The H + OCS potential-energy surface (PES) was used to evaluate the performance of density functional theory by comparing the results to ab initio calculations at the QCISD(T)//UMP2 and UMP2 levels using the aug-cc-pVTZ and 6-311+G(2df, 2p) basis sets. The two major reaction paths on this PES involve formation of OH(2Π) + CS(1Σ) (reaction I) and SH(2Π) + CO(1Σ) (reaction II). Experimental and QCISD(T)//UMP2/aug-cc-pVTZ activation barriers for (II) and reaction enthalpies for (I) and (II) were compared to values calculated by several density functionals (BLYP, B3LYP, B3PW91, BPW91, BP86, and B3P86) using the aug-cc-pVTZ basis set. All DFT/aug-cc-pVTZ predictions, except for the B3LYP prediction of the enthalpy of reaction I, were outside the range of experimental uncertainty. B3LYP predictions were in closest agreement with the experimental values and QCISD(T) predictions. B3LYP, BPW91, and B3PW91 predictions of the rate-limiting barrier to reaction II are within 3.5 kcal/mol of the QCISD(T) prediction, an...