Molecular wave functions for lithium

The method of molecular orbitals has been applied to a discussion of the ground state of Li2. Both the simple product-type functions and the determinantal functions have been used. The final energy value has an error of about 1·3 %. The changes in screening constants in passing from atomic to molecular states is discussed, and empirical rules deduced from this and other work. Provided that all the molecular orbitals used are mutually orthogonal, there is not as much electron exchange between inner and valence electrons as has often been supposed. The importance of this orthogonality in discussion of exchange is emphasized.