Crude Born-Oppenheimer approximation equation

Our problem now is to see how this shape arises from the electronic structure of the atoms involved and to find out what we can about wave functions, energies, charge distributions and so on, all of which will be needed for an understanding of the interactions of these molecules in the liquid and solid states. Even using the Born-Oppenheimer approximation, which allows us first to solve the electronic problem with the nuclei fixed and then to use this result to determine the effective potential in which the nuclei move, exact solution of the Schrodinger equation is out of the question. It is possible, however, with relatively little labour, to see how the particular structure of the water molecule comes about and then, by refining this crude model, to calculate relevant quantities quite accurately. 

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