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Re^5: Some questions about MCQDPT theory

Alex Granovsky

Dear Pavel,

sorry for the delayed feedback.

Yes you need to run this all as a single job,
once for singlets and second time for triplets.
Sure you can reuse converged orbitals as the input
for the MCSCF procedure using guess=moread to speed
things up.

Your first input file should contain at least:

 $contrl scftyp=mcscf mplevl=2 $end
 $det pures=.f. wstate(1)=... $end
 $mcscf cistep=aldet iforb=.t. $end
 $xmcqdpt iforb(1)=-1,1,1 mult=1 inorb=0 $end 

and second should contain at least:

 $contrl scftyp=mcscf mplevl=2 $end
 $det pures=.f. wstate(1)=... $end
 $mcscf cistep=aldet iforb=.t. $end
 $xmcqdpt iforb(1)=-1,1,1 mult=3 inorb=0 $end 

Hope this helps. Please let me know if you need some additional comments.

All the best,

On Tue Oct 16 '12 1:17am, Solntsev Pasha wrote
>Dear Alex.
>One more thing to clarify out talk.
>Should i run XMCQDPT with all function you mentioned or i need run XMCQDPT with  $mcscf iforb=.t. $end  $xmcqdpt iforb(1)=-1,1,1 $end and then use optimized orbitals (XMCQDPT) for XMCQDPT run for singlets and triplets?

>Thank you.

>On Wed Oct 10 '12 10:12pm, Alex Granovsky wrote
>>Dear Pavel,

>>sorry for large delay on my side.

>>>Q1. ok, it sounds very interesting. So, if an order of states from
>>CAS-CI part is 1,1,1,0,1 we can setup kstate(1)=1,1,1,0,1 and
>>basically remove "undesired" state from PT2 part.


>>> Does it make sense?

>>There are some situations when this for sure makes (some) sense.
>>For instance, assume one is dealing with diatomic molecule.
>>The full symmetry group is either Cinfv or Dinfh
>>which is a non-abelian symmetry group. The effective Hamiltonian
>>is thus block-diagonal and (provided one is interested in states of
>>some particular symmetry type) one can remove other states from PT treatment.

>>> Is this equivalent to setting of the AVECOE and WSTATE (XMCQDPT)
>>arrays to be AVECOE(1)=1,1,1,0,1 and WSTATE(1)=1,1,1,0,1. If not, what
>>is the best strategy, to use kstate or avecoe/wstate? Or, maybe, we
>>can just use nstate/wstate/avecoe combination and forget about kstate.

>>No you in general cannot. Both avecoe and wstate applies to renumbered
>>CI states i.e. to state numbers generated after renumbering procedure.

>>In general, kstate and avecoe/wstate are more or less independent.
>>As to NSTATE/kstate, kstate provides the finer control.
>>>Q2. What if those additional eigenvectors contribute to some low
>>lying states? Do we need repeat CASSCF part once again and include
>>those extra states?

>>The answer depends on the magnitude of contribution. If it is large
>>the answer can be "yes, it would be better to do that". As far
>>as I remember this self-consistent procedure of the selection of
>>the states in state-averaging was once discussed a year ago or so
>>on the forum, you may find my older comments on this.
>>>>>Q3: Is it good idea to do SA-CASSCF/XMCQDPT via singlets and triplets
>>>>simultaneously in case of high spin-orbit coupling. Actually, i am
>>>>going to check singlets only and singlets-triplets, but maybe it make
>>>>no sense.

>>>>I'd suggest you to use to use SA-CASSCF averaged over both singlet
>>>>and triplet states to generate the same set of MOs to be used in PT2
>>>>computations. Firefly v. 8.0.0 has some new features specifically
>>>>tailored for these types of jobs which I'll describe in my next post
>>>>to this thread.

>>>Yes, sure.

>>The couple of advises are:

>>1. Use aldet CASCI code with PURES=.f. to generate orbitals with SA-CASSCF.

>>2. Use

 $mcscf iforb=.t. $end
 $xmcqdpt iforb(1)=-1,1,1 $end 

>>to generate and reuse the generated common set of canonical MOs and their energies

>>3. Perform two sets of QDPT calculations, one for singlets:

 $xmcqdpt mult=1 $end 

>>and second for triplets:


 $xmcqdpt mult=3 $end 

>>Hope this helps.

>>All the best,

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