Optimized valence configuration method

The Hartree-Fock method is modified by mixing some important valence electron configurations with the ground-state one 20>. This is called the OVC optimized valence configurations) method. 

The Cl procedure just described uses a fixed set of orbitals in the functions An alternative approach is to vary the forms of the MOs in each determinantal function O, in (1.300), in addition to varying the coefficients c,. One uses an iterative process (which resembles the Hartree-Fock procedure) to find the optimum orbitals in the Cl determinants. This form of Cl is called the multiconfiguration SCF (MCSCF) method. Because the orbitals are optimized, the MCSCF method requires far fewer configurations than ordinary Cl to get an accurate wave function. A particular form of the MCSCF approach developed for calculations on diatomic molecules is the optimized valence configuration (OVC) method. 

A. C. Wahl, PJ. Bertoncini, G. Das, T.L. Gilbert, Recent progress beyond the Hartree-Fock method for diatomic molecules The method of optimized valence configurations, Int. J. Quantum Chem. S1 (1967) 123. 

Curves that go beyond the Flartree-Fock method have been calculated for certain systems, and the list grows monthly. Of special interest is the series on ground [62-64] and excited states [63, 64] of CO, on NaLi and NaLi+ using an extended Flartree-Fock method with optimized double-valence configurations [65], HeLi by a valence-bond method [66], and so on. A quite complete listing of all nonempirical potential-energy curves calculated through 1967 is included in the NBS report [33]. 

Hartree -Fock or Self-Consistent Field (SCF) Method Spin Optimized Self-Consistent Field Method Configuration Interaction Iterative Natural Orbital Method Multi-Configuration SCF Many Body Perturbation Theory Valence-Bond Method Pair-Function or Geminal Method... 

Further comparative calculations by both VB and MO methods on BeEfe have been reported, using a minimal STO basis, with exponents optimized for various r zsz With choice of particular VB configurations, it is shown that a model based on the resonance valence state, including ionic configurations, is particularly useful. Both methods show a localized-pair bond description to be useful. 

---