This question goes in tandem with my previous questions on MCSCF/RASSCF (viewtopic.php?f=9&t=1074) on this forum.
I am trying to run calculation for simple diatomics using RASSCF aiming to get polarizability. Tests with basis sets have shown slow change in alpha values and augQZ looks feasible. However, convergence of alpha values over number of e- in RAS3 and the size of RAS3 has been slow. This accompanies the slow convergence of MCSCF calculations.
N2 (File is attached)
Code: Select all
*CONFIGURATION INPUT .SYMMETRY 1 .SPIN MULTIPLICITY 1 .RAS1 SPACE 1 0 0 0 1 0 0 0 .RAS2 SPACE 1 1 1 0 1 1 1 0 .RAS3 SPACE 4 2 2 1 3 2 2 1 .INACTIVE ORBITALS 1 0 0 0 1 0 0 0 .ELECTRONS 10 .RAS1 HOLES 0 2 .RAS3 ELECTRONS 0 2
alpha_zz: 14.54827311 in atomic units
These values are lower than CCSDT results at the same internuclear distance (10.2351 and 14.8425 a.u.). More tests showed that running with a larger basis, including Rydberg orbitals and also all 14e- as active does not account for this difference in the values of alpha.
Increasing, number of e- to RAS3 increases alpha (10.08330, 14.6112) while increasing size of RAS3 decreases the values (9.9500, 14.36988). (symmetry is broken in the large RAS3 case, with RAS3 set to 63315331)
By performing similar sized CASSCF calculation on MolPro, it is found that there are several low lying states, which are not included when opting for RASSCF with a small RAS3. This is a reason for increasing the size of RAS3. But, then large RAS3 is slow to optimize, which has been explained earlier on my questions.
So, this question on a different approach. Can I do this.
1. Run CASSCF and keep the SIRIUS.RST file
2. Setup my RASSCF calculation as : Keeping RAS2 same as previous CASSCF, 2e- in RAS3 and rest all orbitals to virtual, and simulate something like MRCI. Pass SIRIUS.RST as orbital input.
3. On a side note, can we just do CI calculation and not to orbital optimization ( I way I think is to set the Macro iterations in *OPTIMIZATION to 0).