Energy surfaces, model equations quadratic equation

Newton s method is based on a local quadratic model of the energy surface. The orbital rotations generated by this method therefore behave incorrectly for large rotations. In particular, the Newton equations are not periodic in the orbital-rotation parameters as we would expect fix)m a consideration of the global behaviour of the energy function (10.1.22). The one-electron approximation of the SCF method, by contrast, is correct only to zero order in the rotations, but - provided the effective Hamiltonian (i.e. the Fock operator) is a reasonable one - it exhibits the correct global behaviour. In particular, it is periodic in the orbital rotations. 

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