Post-Hartree-Fock
In computational chemistry, Post-Hartree-Fock methods are the set of methods developed to improve on the Hartree-Fock (HF), or self-consistent field (SCF) method. In general, the SCF procedure makes several assumptions about the nature of the multi-body Schroedinger Equation and its set of solutions:
- The Born-Oppenheimer approximation is inherently assumed. The true wavefunction should also be a function of the coordinates of each of the nuclei.
- Typically, relativistic effects are completely neglected. The momentum operator is assumed to be completely classical.
- The basis set is composed of a finite number of orthogonal functions. The true wavefunction is a linear combination of functions from a complete (infinite) basis set.
- The energy eigenfunctions are assumed to be products of one-electron wavefunctions. The effects of electron correlation, beyond that of exchange energy resulting from the anti-symmetrization of the wavefunction, are completely neglected.
For the great majority of systems under study, in particular for excited states and processes such as molecular dissociation reactions, the fourth item is by far the most important. As a result, the term post-Hartree-Fock method is typically used for methods of approximating the electron correlation of a system.
Usually, post-Hartree-Fock methods give more accurate results than Hartree-Fock calculations, although the added accuracy comes with the price of added computational cost, of course.
List of post-Hartree-Fock methods
Moller-Plesset perturbation theory (MP2, MP3, MP4, etc.)
Multi-configurational self-consistent field (MCSCF)
Coupled cluster (CC)
Quadratic configuration interaction (QCI)
Configuration interaction (CI)