7.8.2 SA-CASSCF and MRCI

The following calculation performs state-averaged CASSCF and subsequent MRCI calculations for the ground and first excited state of the OH radical. A full valence active space is used.

Input: oh_runmrci1.com

Output: oh_runmrci1.out

The following table is printed at the end of the output:

 RESULTS

 METHOD  STATE     S       ENERGY    DIPX  DIPY     DIPZ
 CASSCF    1.2   0.5   -75.41331789   0.0   0.0   0.67158730
 CASSCF    1.3   0.5   -75.41331789   0.0   0.0   0.67158730
 CASSCF    1.1   0.5   -75.24125256   0.0   0.0   0.69975340
 MRCI      1.2   0.5   -75.55518444   0.0   0.0   0.66457191
 MRCI+D    1.2   0.5   -75.56014871   0.0   0.0   0.66457191
 MRCI+P    1.2   0.5   -75.55853208   0.0   0.0   0.66457191
 MRCI      1.3   0.5   -75.55518444   0.0   0.0   0.66457191
 MRCI+D    1.3   0.5   -75.56014871   0.0   0.0   0.66457191
 MRCI+P    1.3   0.5   -75.55853208   0.0   0.0   0.66457191
 MRCI      1.1   0.5   -75.39442202   0.0   0.0   0.70484623
 MRCI+D    1.1   0.5   -75.40040680   0.0   0.0   0.70484623
 MRCI+P    1.1   0.5   -75.39846312   0.0   0.0   0.70484623

This calculation performs MRCI calculations for both $^2\Pi_x$ and $^2\Pi_y$. The procedure is not clever enough to recognize that they are degenerate. However, one can easily modify the input to eliminate this drawback.

Input: oh_runmrci2.com

Output: oh_runmrci2.out

This produces

 RESULTS

 METHOD  STATE     S       ENERGY    DIPX  DIPY     DIPZ
 CASSCF    1.2   0.5   -75.41331789   0.0   0.0   0.67158730
 CASSCF    1.3   0.5   -75.41331789   0.0   0.0   0.67158730
 CASSCF    1.1   0.5   -75.24125256   0.0   0.0   0.69975340
 MRCI      1.2   0.5   -75.55518444   0.0   0.0   0.66457191
 MRCI+D    1.2   0.5   -75.56014871   0.0   0.0   0.66457191
 MRCI+P    1.2   0.5   -75.55853208   0.0   0.0   0.66457191
 MRCI      1.1   0.5   -75.39442202   0.0   0.0   0.70484623
 MRCI+D    1.1   0.5   -75.40040680   0.0   0.0   0.70484623
 MRCI+P    1.1   0.5   -75.39846312   0.0   0.0   0.70484623

You may want to extend the active space to include the $2\pi$ orbitals. This can be achieved by setting the variable OCC.

Input: oh_runmrci3.com

Output: oh_runmrci3.out

For accurate calculations of the electronic transition moment, also the $1\delta$ orbitals contribute significantly. These are in symmetry 1 ( $\delta_{x^2-y^2}$) and 4 ($\delta_{xy}$). In order to force the $5a_1$ orbital to become the $\delta$, we must use the SYM directive in the SCF calculation. Since it is not possible to insert this into the procedure, we must write the SCF input explicitly.

Input: oh_runmrci4.com

Output: oh_runmrci4.out

Note that this calculation is quite expensive!