...到场点的距离； o ––真空中的电容率 r ˆ ––单位矢量（如图，由场源指向场点）； （2） 点电荷系(point charge group) 2 1 1 1 2 4 ˆ 4 ˆ r r q r r q E o i o i i + 2 2 2 2 4 ˆ r r q o +……
They belong to C_ (2v) localsymmetry. From the point of view of point-chargemodeltheligandfieldsemi-quantitativecalculation is applied to molecules with C_ (2v) point groupsymmetry.