Multi-configurational self-consistent fields wave functions

A modification of this scheme has been used for optimizing excited states of multi-configurational self-consistent field wave functions, see H. J. Aa. Jensen and H. Agren, Chem. Phys. 104, 229 (1986). 

Henne Hettema, Hans Jorgen Aa. Jensen, Poul Jorgensen, and Jeppe Olsen (1992). Quadratic response functions for a multi-configurational self-consistent-field wave-function. J. Chem. Phys. 97, 1174-1190. 

J. Olsen, P. Jprgensen, Time-dependent response theory with applications to self-consistent field and multi-configurational self-consistent field wave functions, in Modern Electronic Structure Theory, Part 11, D. R. Yarkony, Ed., World Scientific, Singapore, 1995, p. 857. 

The Multi-configuration Self-consistent Field (MCSCF) method can be considered as a Cl where not only the coefficients in front of the determinants are optimized by the variational principle, but also the MOs used for constructing the determinants are made optimum. The MCSCF optimization is iterative just like the SCF procedure (if the multi-configuration is only one, it is simply HF). Since the number of MCSCF iterations required for achieving convergence tends to increase with the number of configurations included, the size of MCSCF wave function that can be treated is somewhat smaller than for Cl methods. 

By calculating A.U (R) and Al/ (i ) separately, we can straightforwardly calculate the total adiabatic correction V (R) for any isotopes of A and B. The adiabatic corrections are calculated by numerical differentiation of the multi-configurational self-consistent field (MCSCF) wave functions calculated with Dalton [23]. The nurnerical differentiation was performed with the Westa program developed 1986 by Agren, Flores-Riveros and Jensen [22],... 

However, although, starting from this point, many sophisticated methods for wave function expansion, for example, the coupled cluster approach, multi-configuration self-consistent-field method or multi-reference Cl methods, have been developed, the correlation problem faced many computational limitation, some of them almost insurmountable, due to the immense number of integrals to be evaluated. 

Although the correlation consistent sets were developed to describe correlated wave functions, they also provide a very systematic description of Hartree-Fock as well as simple valence multi-configurational self-consistent field (MCSCF) wave functions for molecules. This should not be too surprising. The radial and angular space spanned by the HF and... 

They showed that the dimerized bond should be considered as a singlet diradical. Therefore, a qualitatively correct description of the dimer requires at least a generalized valence bond, GVB-PP132, or a two configuration self-consistent field (TCSCF)33 wave function. More recently, Paulus29 performed a more exhaustive multi-reference analysis of silicon clusters and reconfirmed this conclusion. 

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