| Restricted Open-shell Hartree-fock |
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As with restricted Hartree-Fock theory for closed shell molecules, it leads to a Roothaan Equations written in the form of a Generalized Eigenvalue Problem : Where F is the so-called Fock Matrix , C is a matrix of coefficients, S is the Overlap Matrix of the basis functions, and is the (diagonal, by convention) matrix of orbital energies. Unlike restricted Hartree-Fock theory for closed shell molecules, the form of the Fock matrix is not unique. Different so-called canonicalisations can be used leading to different orbitals and different orbital energies, but the same total wavefunction, total energy, and other observables. In contrast to Unrestricted Hartree-Fock (UHF), the ROHF wave function is a satisfactory eigenfunction of the total spin operator - . Developing Post Hartree-Fock methods from the ROHF wave function has proved to be more difficult than from the UHF wave function, but a restricted open shell version of Møller-Plesset Perturbation Theory to second order (ROMP2) has been developed. |
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