In order to simplify discussion, it is suggested to merge ∆Ex and ∆Erep together as The time cost in steps ( ) and ( ) is negligible. The time consumed in (3) just corresponds to one SCF iteration and hence the cost is also trivial. Typically, the overall cost of sobEDA is merely about two times of regular single point calculation for the entire system. The low cost of sobEDA enabling it to be easily employed for systems consisting of hundreds of and even more than one thousand atoms with a 2-zeta basis set plus polarization functions.