Configuration interaction method, energy

The difference between the Hartree-Fock energy and the exact solution of the Schrodinger equation (Figure 60), the so-called correlation energy, can be calculated approximately within the Hartree-Fock theory by the configuration interaction method (Cl) or by a perturbation theoretical approach (Mpller-Plesset perturbation calculation wth order, MPn). Within a Cl calculation the wave function is composed of a linear combination of different Slater determinants. Excited-state Slater determinants are then generated by exciting electrons from the filled SCF orbitals to the virtual ones ... 

If we choose only one determinant built from the lowest /2 SCF-orbitals, the "configuration interaction method will naturally give us Wq = Ao with the energy eigenvalue q as the best groimd-state description. This is clearly identical with the SCF result of the last section. 

Figure 10.69. Potential energy curves for the five lowest energy electronic states of CH, calculated by Lie, Hinze and Liu [188] using an extended configuration interaction method.

Other theoretical studies of ozone and its excited states have been previously reported and also indicate a relatively low lying state corresponding to a six jr-electron cyclic structure. In particular, recent ab initio calculations using the generalized valence bond and configuration interaction methods with a double zeta basis set, predict that trioxirane lies about 35 kcal/mol higher in energy than ozone but that it is a potential minimum. 

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