CC3 oscillator strength

Dear MRCC Developers,

I am trying to calculate CC3 oscillator strength.My input file is as following
________________________________________________________________________
# LR-CC(3)transition moment calculation
basis=TZVP
calc=cc3
mem=10000MB
nsing=2
dens=6
cctol=6
symm=B2

geom=xyz
7

H 0.912650 0.000000 1.457504
H -0.912650 0.000000 1.457504
H 0.000000 -1.585659 -1.038624
H 0.000000 1.585659 -1.038624
C 0.000000 0.000000 0.859492
C 0.000000 -0.651229 -0.499559
C 0.000000 0.651229 -0.499559
_______________________________________________________________
But is giving the following error
##################################################
Executing mrcc...
Approximate CC methods are not implemented for excited states!

Fatal error in mrcc.
Program will stop.
######################################################
Is it the case that oscillator strength is not available for CC3?
Any suggestion will be of great help

Best regards,
Achintya

Dear Achintya,
Yes, it is. Perturbative CC methods, such as CC3, are not implemented for excited states. Please see Sect. 6.6 in the manual for the methods which are available for excited states.

Dear Prof. Kallay,

Thank you for the kind reply.

With best regards,
achintya

Dear Mihály,
I have always been confused by this convention in MRCC. CC(n)-1a, CC(n)-1b, CCn, and CC(n)-3 methods are not perturbative, but are iterative approximations to the full CC(n) algorithm.

Is MRCC really setting up the CC3 diagrams to be computed perturbatively rather than iteratively?

Thanks!
Nate

Dear Nate,
For the perturbative CC methods, such as CC3, the diagrams including the highest-level excitations are evaluated pertubatively. But these methods are only available for ground states, excitation energy and oscillator strength calculations are no possible.

Mihály,
Sorry, I am not such an expert in coupled cluster implementations. For clarification, you are writing that even though convergence of, for example, CC3 amplitudes/energies are iterative, the method that the MRCC code uses to generate diagrams for partial excitation CC methods involves perturbation theory. This excludes them from being used with ROHF references. Correct?