Semi-empirical quantum chemistry method
| Electronic structure methods |
|---|
| Valence bond theory |
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Coulson–Fischer theory Generalized valence bond Modern valence bond theory |
| Molecular orbital theory |
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Hartree–Fock method Møller–Plesset perturbation theory Configuration interaction Coupled cluster Multi-configurational self-consistent field Quantum chemistry composite methods Quantum Monte Carlo |
| Density functional theory |
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Time-dependent density functional theory Thomas–Fermi model Orbital-free density functional theory Adiabatic connection fluctuation dissipation theorem Görling-Levy pertubation theory Optimized effective potential method Linearized augmented-plane-wave method Projector augmented wave method |
| Electronic band structure |
|
Nearly free electron model Tight binding Muffin-tin approximation k·p perturbation theory Empty lattice approximation GW approximation Korringa–Kohn–Rostoker method |
Semi-empirical quantum chemistry methods are based on the Hartree–Fock formalism, but make many approximations and obtain some parameters from empirical data. They are very important in computational chemistry for treating large molecules where the full Hartree–Fock method without the approximations is too expensive. The use of empirical parameters appears to allow some inclusion of electron correlation effects into the methods.
Within the framework of Hartree–Fock calculations, some pieces of information (such as two-electron integrals) are sometimes approximated or completely omitted. In order to correct for this loss, semi-empirical methods are parametrized, that is their results are fitted by a set of parameters, normally in such a way as to produce results that best agree with experimental data, but sometimes to agree with ab initio results.