A comparison of DLPNO-CCSD(T) and CCSD(T) method for the determination of the energetics of hydrogen atom transfer reactions

Abstract

We have assessed the accuracy of the DLPNO-CCSD(T) method against the CCSD(T) method in determining the barrier heights and reaction energetics for a series of hydrogen atom transfer reactions. Our reaction list consists of both closed shell and open shell prototype systems. For closed shell systems, the difference in calculated barrier heights at DLPNO-CCSD(T)/aug-cc-pVnZ and CCSD(T)/aug-cc-pVnZ (n = D, T and Q) level of theory were found to be always less than ∼0.8 kcal mol−1 with a standard deviation of 0.23, 0.18 and 0.16 kcal mol−1 at aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets, respectively. The standard deviation of the same for the open shell systems were found to be 0.43, 0.79 and 0.91 kcal mol−1 at aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets, respectively. Furthermore, the study reveals that a modification is needed in the recommended value of the parameter “TcutPNO” while using the DLPNO-CCSD(T) method for reactions exhibiting multireference character.