Ceilidh ... Re^7: CASSCF optimized orbitals are not orthogonal for XMCQDPT

Firefly and PC GAMESS-related discussion club

Re^7: CASSCF optimized orbitals are not orthogonal for XMCQDPT

Do you mean that all xmcqdpt calculations with restricted excitations don't make sense or just if they're perfomed with unorthogonal orbitals? Also, could you help me explaining
how to visualize xmcqdpt spectra in Chemcraft, because i can't do it myself?
On Sun Mar 27 '11 4:24pm, Vladimir A. Mironov wrote
---------------------------------------------------
>FORS-MCSCF and CASSCF are synonyms.
>I mean that your MCSCF calculation with restricted excitations is not a CASSCF. You would easily get an arbitrary result from the XMCQDPT2 run.

>On Sat Mar 26 '11 10:45pm, Gena wrote
>-------------------------------------
>>But won't it lead to a dramatical rise of CSFs? I understood from previous CASSCF calculations that CSFs with more than 4 excitations almost don't contribute to the excited states i'm interested in at all.
>>Also, the other system i mentioned doesn't cause such problems, and i also use (12,12) active space with only 4 excitations there.

>>On Sat Mar 26 '11 9:06pm, Vladimir A. Mironov wrote
>>---------------------------------------------------
>>>I guess, the problem arises from the IEXCIT=4 keyword in $DRT group. As far as I know, XMCQDPT calculation is only compatible with CASSCF reference wavefunction. Replace IEXCIT=4 with fors=.t.

>>>On Sat Mar 26 '11 4:56pm, Gena wrote
>>>------------------------------------
>>>>On Sat Mar 26 '11 4:37pm, sanya wrote
>>>>-------------------------------------
>>>>>Probably, you have included CASSCF natural orbitals instead of optimized. Both sets of orbitals are punched; OPTIMIZED are in the last $VEC group.

>>>>>An alternative is to set INORB=2 to ignore orthogonality check. But I'm not sure about the results with nonorthogonal orbitals.

>>>>>On Fri Mar 25 '11 7:31pm, Gena wrote
>>>>>------------------------------------
>>>>>>On Fri Mar 25 '11 5:58pm, Gena wrote
>>>>>>------------------------------------
>>>>>>>Hello!
>>>>>>>I try to calculate electronic absorption spectra using XMCQDPT. But after CASSCF calculation is successfully finished, XMCQDPT calculation with optimized MOs from CASSCF PUNCH-file fails in the very beginning listing unorthogonal to each other orbitals, and as i see it - they're all unorthogonal. Firefly also advises me to set INORB=0 to reorthogonalize them. But as XMCQDPT isn't parallel, it isn't convenient. Moreover, i don't understand the difference, i thought that would be the same CASSCF calculation, only in serial mode. Sorry for stupid question, i'm just studying multiconfigurational methods. What am i doing wrong?
>>>>Thank you, Sanya! No, of course i understand the difference between optimized and natural orbitals. Moreover, i tried to use natural orbitals to see what error would it cause. And i got immediately I/O error.
>>>>The interesting for me thing is that i tried another compound with the same algorithm of actions, and the xmcqdpt calculation started successfully, passing orthogonality check without problems! (Though it isn't over yet).
>>>>I too dislike to ignore unorthogonality as i really wanna get reliable results, because i need them in my experimental work.

Sun Mar 27 '11 7:29pm

This message read 964 times