SA-CASSCF

The OH applications discussed here involve transitions between valence states. The application of the SA-CASSCF/MRCI approach to valence-Rydberg transitions poses additional problems. The requirement of adding diffuse orbitals to the one-particle basis set to describe the Rydberg character is well known, so we focus on the requirements for the n-particle treatment. An excellent system for such a calibration is the AlH molecule, which can be treated very well as a four-electron system, simile L-M intershell correlation introduces only a small bond contraction. The FCI study of AlH included the and A H valence states and the Rydberg state (see... 

Fig. 2). A relatively small basis set was used, but one that was capable of describing the Rydberg character of the C state. The AMfl-X E transition moment is well described by an SA-CASSCF procedure that includes the A13s and 3p and H Is orbitals in the CASSCF active space. As the C E" state is derived from the S(3s 4s ) state of Al, the active space must be expanded beyond the valence orbitals. When the 4s is added to the active space, all MRCI properties except the dipole moment of the C state are in good agreement with the FCI. Since the C E state is very diffuse, small...

Fig. 7 Two-dimensional spectrochemical series for Cr-X (X = F, Cl, Br, I) tetrahedral and octahedral complexes from ATT /FT results based on SA-CASSCF calculations. Values reported from AOM interpretations of d-d absorption spectra of Cr(NH3)5X2+ complexes are given by starts (adopted from D. W. Smith, Structure and Bonding, 35, 87-118 (1978), p. 92, Table 1)...

Fig. 17 NEVPT2-based AILFT d-orbital levels schemes in comparison with those from SA-CASSCF for Ni(dtc)2 and Ni(acac)2 reflecting the Orgel effect with dyz > dxz for out-of-phase (dtc-) and the dxz > dyz in-phase (acac ) the energy of dz2 was taken as the energy reference...

Not unexpectedly, orbital energies from SA-CASSCF calculations are very close to ones obtained using AILFT and AOM parameters adjusted to CASSCF results. 

Fig. 4 Potential energy curves of 1,2 LiF relative to the minimum of the lowest curve. The (2 Z+) curves of FCI, SA-CASSCF, SS-MRPT2 and SDS-MS-MRPT2 are in solid (dashed) black, blue, olive and violet, respectively. Inset shows magnified view of the region near avoided crossing...

Fig. 5 Deviations of SA-CASSCF (black), SS-MRPT2 (red) and SDS-MS-MRPT2 (blue) from FCI for the energy gap between and I Z ofLlF...

For an optimized SA-CASSCF wavefunction, E = 0 but only the weighted average of the anti-symmetric... 

Using an optimized SA-CASSCF wavefunction to calculate the Hessian for the time-dependent vector is a rough approximation again, we show in Sect. 4.2 that the numerical fitting of the hypersurface along the trajectory corrects most of the error. 

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. 

Table 3.3 SA-CASSCF and XMCQDPT2 vertical excitation energies, calcuiated using the two active spaces described in Sect. 3.2, compared with values from previous high-ievel ab initio calcu-iations and experimentai vaiues...

Table 7.1 SA-CASSCF, ZO-QDPT and MRCI polarizabilities in atomic units at the ground state equilibrium geometry...

Brown et al. have performed state-average complete active space self-consistent field (SA-CASSCF) calculations of the polarizability and first hyperpolarizability of novel alkyl-substituted 4-quinopyran twisted 7i-system chromophore (Fig. 1, 2). In the gas phase, the ground electronic... 

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