CCSD on triplet excited state

[garix]

Dear all,

I would like to run a CCSD calculation for the triplet excited state, however, the output file provides me with the following error, just after the optimization of the GS state amplitude:

  ----------------------------------------------------------------------------

    Check for potential start vectors for CCSD eigenvalue problem:

     type  irrep  state  model     file
    ------------------------------------------------------------------------
 Illegal state input for CCSD     excitation energies:
 irrep, column:                     1                     1
 multiplicity :                     3
 charge diff. to GS:                     0

========================
 internal module stack:
------------------------
    ccsdf12
    ccsdrspim
========================

 Illegal state input in ccsdrspim!
 ccsdf12 ended abnormally

I ran the same calculation for the singlet and I did not go through any problem.
The part of the control file regarding the excited state calculation is the following:

$ricc2
  ccsd
$excitations
   irrep=a multiplicity=3 nexc=1

Thanks for your help.

Gaetano

[mas]

Do you run open shell or closed shell calculation?

[garix]

I tried both RHF and UHF reference. The former provided me with that error. The latter stopped just after the calculation of the CCS excitation energies, without showing any error:

======== LINEAR CC RESPONSE SOLVER ========

    threshold for convergence: 1.00E-06
    maximum number of simultaneous Jacobi matrix transformations:  1

     summary of start vectors generation:
     -------------------------------------------
     type of solution vectors      : RE0
     symmetry                      : a
     number of vectors requested   :     1
     number of vectors generated   :     1
     -------------------------------------------


    Iter  #Vectors  time (min)    max. residual

[mas]

I guess you cannot calculate triplet excited states with RHF reference.  For the UHF reference, did you get any error message in the log file?

[garix]

No, no error. I tried to rerun the UHF reference calculation increasing the memory. So far, the only error is ccsdf12 step seems to have been in serious trouble but the calculation keeps running. Let's see.

Thank you

[Arnim]

Hello,

at this time (version 7.5) the implementation is currently restricted to closed–shell singlet excited states.

And indeed tripet excitations can (in principle) be calculated from RHF wave functions.

Best
Arnim

[garix]

Thank you very much for your help guys.

Best,

Gaetano