1. The individual fragments (in complex geometry) first form a promolecule state of the entire system, whose occupied orbitals simply correspond to union of occupied fragment orbitals, and wavefunction of the promolecule state can be viewed as Hartree product of the fragment wavefunctions. The variation of electrostatic energy, exchange energy, correlation energy and dispersion correction in this stage directly defines ∆Eels, ∆Ex, ∆EDFTc and ∆Edc terms of sobEDA method, respectively. Note that in this stage kinetic part of system energy keeps unchanged, because KS-DFT framework evaluates kinetic energy of non-interacting electrons as sum of expectation values of kinetic operator for occupied orbitals, which are completely unperturbed in this stage. 3. In the last stage, by allowing occurrence of intrafragment electron polarization and charge transfer between fragments, frozen state relaxes to final state. The corresponding total energy variation corresponds to orbital interaction term (∆Eorb) in sobEDA.