Utilization of generalized energy-based fragmentation method on the study of hydrogen abstraction reactions of large methyl esters

Accurate reaction energies and barrier heights are essential for the construction of reliable combustion kinetics models of various fuels. Nevertheless, the computational cost for electronic energy calculations using high-level ab initio methods increases dramatically with the size of molecules. A solution to this problem is to utilize a generalized energy-based fragmentation (GEBF) approach, as it has been found to be effective in reducing the scaling of the computational cost in calculation of energetics and other molecular properties for many large molecules, clusters, and crystals with various quantum chemistry methods. This work attempts to apply this GEBF approach in the study of one important type of reactions of large methyl esters, i.e., the hydrogen abstraction reactions by hydrogen atoms. The energies of stationary points on the potential energy surfaces were examined using both conventional quantum chemistry methods and the GEBF method at the QCISD(T)/CBS// M06-2X/6-311 + + g(d,p) level for CnH2n+1COOCH3 (n = 4, 5) + H reactions. The results show that the unsigned energy deviation of the GEBF method from the conventional method is less than 0.1 kcal/mol, while the computational time is greatly reduced, e.g. up to 90% at the QCISD(T)/cc-pVTZ level. Based on the quantum chemistry calculations, rate constants of the hydrogen abstraction reactions of CnH2n+1COOCH3 (n = 4, 5, 8) by H atoms were computed.