As the size of the molecules increased, inclusion of nonbonded steric effects became increasingly important. The steric interactions were described by the same linear relationship in Eq.12 with the negative bond orders. Unless otherwise stated, we elect to derive parameters for BEBOP for the geometry optimization obtained from UB3LYP/6-311G(2d,d,p) calculations. All ROCBS-QB3 and ROHF calculations were performed in GAUSSIAN16(Revision C.01).