New efficient multi-level electronic structure methods (MLSEn) for atomization energies and reaction energy barriers

We have developed a new set of multi-level methods with scaled energies (MLSEn) for calculating the atomization energies and reaction energy barriers. The MP2 and QCISD(T) theories with correlation-consistent basis sets were used to obtained various energy components, and simple scaling schemes were used to optimize the scaling factors against a database of 109 atomization energies. The resulting methods were also tested on 21 energies of reactions, and 42 barrier heights. The most accurate methods give mean unsigned errors of 0.78 kcal/mol for atomization energies (MLSE4) and 0.61 kcal/mol for barrier heights (MLSE1).