CASSCF method state-averaged

C=C stretch 80 C-13 chemical shifts 22, 53 C60 31,32 C60O isomers 54 carbon dioxide 120, 182 carbon monoxide 175,191 carbonyl series 84 carbonyl stretch 84, 220 in solution 244 Carmichael 136 Carpenter 152, 196 Cartesian coordinates 52, 286, 287 CASSCF keyword 228 CASSCF method 228,229,230,231, 232,233, 234,235 state-averaged 233... 

In this last section we will take a short sidestep from the main subject of this chapter to look at another aspect of computational chemistry where multiconfig-urational methods, in particular CASSCF, come in very handy, i.e., the description of excited states. Indeed, one of the nice features of the CASSCF method is that it can generally be used for excited states as well as for the ground state. All it takes is to optimize a set of orbitals for the excited state in question (which is not always straightforward in cases where different roots are close in energy and may flip [10]) or, alternatively, for an average of a set of excited states. It is important to realize, however, that the calculation of excited states imposes additional demands on the active space, other than to include all near-degeneracy effects. The rule is simple and self-evident all orbitals that are either populated... 

With the exception of the 1 11 state the CASSCF results have been obtained by the state-average method. 

The electronic wavefunction was evaluated using the state averaged complete active space self-consistent field (SA-CASSCF) method [49, 50], as implemented in the Molpro [51] electronic structure package. We used the 6-31G basis set [52] and an active space of two electrons in two orbitals with equally weighted averaging over the lowest three singlet states, i.e., SA-3-CAS(2/2)/6-31G. ... 

Minima and transition states (TSs) were optimized using the state specific complete active-space self-consistent field (SS-CASSCF) method. MECIs were optimized using state-averaged CASSCF (SA-CASSCF) [71] with equal weighting given to the two states forming the Cl. 

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