I have to calculate the S1 - T1 energy gap using coupled cluster (STEOM-DLPNO-CCSD) in ORCA. The output file contains only singlet energies. IROOT=... (no notation singlet or triplet). I tried adding "DoTriplet true", but it didn't work. I would like to know how to do it with an example of an input file.

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    $\begingroup$ What version of ORCA are you using? $\endgroup$
    – wzkchem5
    Commented Mar 23, 2022 at 18:21
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    $\begingroup$ Darya can you please post your input and output files here? $\endgroup$ Commented Mar 25, 2022 at 11:15
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    $\begingroup$ @SRMaiti Can you let us know if the question gets answered there? I think users of the ORCA forum should be encouraged to come here, rather than the other way around. Darya, you said you have some other problems when doing calculations on large systems, I think you should ask that as a separate question, with the input and output files shown in a code block. $\endgroup$ Commented Mar 25, 2022 at 20:45
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    $\begingroup$ @NikeDattani Yes I agree, but for very specific technical details, Orca forum is probably the best because the developers would know about the keywords (and the developers are not on this site so far). This question has not been asked there so far. $\endgroup$
    – S R Maiti
    Commented Mar 26, 2022 at 12:31
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    $\begingroup$ @SRMaiti MMSE only started recently, a few months into the pandemic. At that time, no developers of any software were on this site. What you're saying about ORCA, was also true about VASP, qESPRESSO, Gaussian, LAMMPS, etc. Now we have 300+ questions about VASP, 200+ questions about qESPRESSO, etc. The site wouldn't exist if we asked everything in existing forums. At the time that you wrote that comment, what about the answer that was written 1 day before, from an ORCA developer that was the first to implement the method in the question's title (at least for singlet states)? $\endgroup$ Commented Dec 10, 2022 at 14:16