Hartree-Fock approximation energy eigenvalue

The correlation energy for a certain state with respect to a specified Hamiltonian is the difference between the exact eigenvalue of the Hamiltonian and its expectation value in the Hartree-Fock approximation for the state under consideration. 

A measure of the extent to which any particular ab initio calculation does not deal perfectly with electron correlation is the correlation energy. In a canonical exposition [79] Lowdin defined correlation energy thus The correlation energy for a certain state with respect to a specified Hamiltonian is the difference between the exact eigenvalue of the Hamiltonian and its expectation value in the Hartree-Fock approximation for the state under consideration. This is usually taken to be the energy from a nonrelativistic but otherwise perfect quantum mechanical procedure, minus the energy calculated by the Hartree-Fock method with the same nonrelativistic Hamiltonian and a huge ( infinite ) basis set ... 

The best energy attainable within this approximation is the so-called Hartree-Fock (HF) energy. The difference between this energy and the exact eigenvalue for the electronic hamiltonian operator is denoted as correlation energy. Several schemes have been proposed in order to improve this situation. For the systems... 

Fig. 3. A comparison of the eigenvalues of the outermost valence electrons for Pu using relativistic, semi-relativistic and non-relativistic kinematics and the local density approximation (LSD). Dirac-Fock eigenvalues after Desclaux are also shown. The total energies of the atoms (minus sign omitted), calculated with relativistic and non-relativistic kinematics are also shown. HF means Hartree Fock...

The wave eigenfunctions and energy eigenvalues were obtained by real space electronic state calculations, which were performed by the use of the program code SCAT of the DV-Xx molecular orbital (MO) cluster method with the Hartree-Fock-Slater approximation [8,9]. In the method, the exchange-correlation term Vxc in the one-electron Hamiltonian was expressed in terms of the statistical local potential (1),... 

These are known as the Roothaan equations. They represent an algebraic equivalent to the Hartree-Fock equations. The approximate eigenvalues represent orbital energies. By Koopmans theorem, — approximates the ionization energy for an electron occupying orbital a. The orbital energies can be determined directly Ifom the n roots of the secular equation... 

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