Donor-acceptor interactions of the model water molecule

Donor-acceptor interactions of the model water molecule 

To start with, we assume that the HO with m = 1 will be used for the dative bond. For it we use the estimates eq. (4.10) for the density ESVs. This may be termed as a harmonic approximation in terms of the ESV x. The energy of the dative bond is then given by 

With these definitions we get a correction for the one-center energy of the water oxygen atom due to partial electron density transfer to the acceptor orbital  

The limiting values of s2 correspond either to the pure p-character of the dative bond HO (s2 = 0) pointing normally to the water molecular plane or to approximately sp2 HO directed along the 6 2 axis of the water molecule. The hybridization manifold structure allows for the determination of the direction of the HO lend for the dative bonding for each specific value of si. According to eq. (3.61) we have  

With the fixed value of s this defines the projection of the dative bonding HO (m = 1) on the C-2 axis (x) the rest of the p-weight comes from the z-component of the HO  

---