The LCFC Approach to Geminal Interactions

We shall now illustrate how this approach, designated the Linear Combination of Fragment Configurations (LCFC) approach, can be applied to diverse chemical problems. 

The LCFC approach provides the basis for the development of an overview of the shapes of AXj and AX3 molecules. In order to maximize simplicity, we have developed a model which restricts the number of basis set conHgurations in such a manner that only the key electronic changes accompanying the bending of a linear tri-atomic molecule or the pyramidalization of a flat tetraatomic molecule are considered. Hie various features of our model are the following  

We first consider the case of OX2 as an example. The configuration of the central atom is shown below. Note that two electrons are placed in a 2 py orbital to reproduce the 2py lone pair of linear OX2 and one electron is placed in each of the 2px and 2 s AO s which constitute the two valence AO s of 0 utilized in bonding in 

Note that single occupancy is assigned to AO s which are principally utilized in forming the sigma bonds in linear OX2- 

Let us now identify the MO interaction which is turned on upon bending in the case of H2O. By reference to Fig. 40, we can isolate this interaction as being the one between the 2py AO and symmetric MO, spannii the two hydrogens. The 

---