State-averaged CAS

Perform a series of state-averaged 4,4 CAS calculations on the ground state, using the active space you have selected. Normally, a CAS calculation optimizes the orbitals and hence the wavefimction for the state of interest (as specified by the NRoot option). However, in a state-averaged CAS, orbitals are optimi. ed to provide the best description of the specified group of states as a whole that is possible with a single set of orbitals... 

We will run a series of state-averaged CAS(4,4) calculations (the option is StateAverago) on the ground state structure, using this sequence of basis sets 3-21G, 4-31G, 6-31G(d) and 6-31+G(d,p). Begin the first computation using the wavefunction computed in the RHF calculation. 

The QMC calculations are done with Jastrow-Slater wave functions using a single determinant (JSD), or a state-average (SA) or state-specific (SS) complete-active-space multideterminant expansion (JCAS). The lists of parameters optimized by energy minimization in VMC are indicated within square brackets Jastrow (J), CSF coefficients (c), and orbitals (o). For comparison, the DMC results of Ref. [13] obtained with state-average CAS(6,5) wave functions and a Gaussian basis set are also shown... 

It remains to check whether these conclusions are generally true for other systems. It would be indeed desirable for calculations on large molecular systems if accurate DMC excitation energies could be obtained with state-specific or state-average CAS expansions without the need of an expensive reoptimization of the determinantal part of the wave functions in QMC. 

Run a final state-averaged calculation at the fuUy-optimized conical intersection using the 4-31G basis set and P to predict the energies of the two states and view the configuration coefficients. (This step will not be necessary if you chose to use P for the final conical intersection optimization job you ll find the relevant output in the CAS output for the final optimization step, preceding the table giving the stationary point geometry.)... 

CAS F calculations are not a universal solution to symmetry-breaking of the wave functions, and for such weak resonance problems it is far more reliable to start from state average solutions which treat on an equal footing the two configurations which interact weakly. 

Chemicals are stored in a laboratory with volume V (m ). As a consequence of poor laboratory practices, a hazardous species, A. enters the room air (from inside the room) at a constant rate mA(g A/h). The room is ventilated with clean air flowing at a constant rate V ai,(m- /h). The average concentration of A in the room air builds up until it reaches a steady-state value CA,r(g A/m"). 

Figure 8.10(b) Generalized isoconcentration contours for (mg/L) in atmospheric precipitation of the contiguous United States in 1995, based on the plotted average Ca- concentrations reported for stations in the National Atmospheric Deposition Program/ National Trends Network (1996). High mid-continent Ca values in precipitation are chiefly from windblow carbonate and sulfate salts. 

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. ... 

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