Wave function optimization

T.H. Fischer and J. AlmlOf, General methods for geometry and wave function optimization, J. Phys. 

There exists today an alternative approach which has made MCSCF calculations on excited states feasible, also for rather large systems. A method has been developed which makes it easy to obtain orthogonal wave functions and transition densities from CASSCF wave functions optimized independently for a number of excited states of different or the same symmetry as the ground state. The method has been called the CAS State Interaction (CASSI) method. It will be briefly described below. 

The projection operator A produces an antisymmetrized wave function. Optimizing the linear coefficients C so as to minimize the energy yields a secular determinant whose eigenvalues are upper bounds to the energies of the N lowest states of the system and whose eigenvectors are approximations to the corresponding wave functions. The nonlinear parameters at are usually optimized by some search procedure. 

Figure 13-2. A figure presenting the procedure of the CC/MM wave function optimization...

MCSCF wave function optimizations afe the energy to second order in the variational parameters (orbital and configurational coefficients), analogously to the second-order SCF procedure described in Section 3.8.1, using Newton-Raphson based motbods descrihed in Chapter 14 tO force -convergence to a minimum. ... 

Shepard, R., Discussion of some multiconfiguration wave function optimization methods , 183rd ACS National Meeting, March 1982. 

Snajdr and Rothstein compared a number of properties including the average interelectronic distances and multipole moments of wave functions optimized by variance minimization to those optimized by energy minimization [155]. They... 

Wave function optimization Variance minimization, energy minimization, and their combination with fixed sample points. 

R. Shepard, I. Shavitt, and J. Simons, Comparison of Convergence Characteristics of Some Iterative Wave Function Optimization Methods, J. Chem. Phys. 76, 543-557 (1982). 

T. H. Fischer, J. Ahnlof. General Methods for Geometry and Wave Function Optimization. J. Phys. Chem., 96 (1992) 9768-9774. 

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