In the complexes with the water and ammonia molecules, the companion atom was placed in the direction of the lone electron pair. Finally, in the ethylene dimer, the molecules were placed parallel (stacked) to each other. Such a choice of complexes and geometries should be very demanding for S 2 approximation since the electron density near lone pairs of water and ammonia, as well as the density of π electrons of C 2 H 4 should be strongly diffused. Also, for atoms of Be and Mg, the electronic densities are diffused.