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# Dirac interface and symmetry groups

2 years 4 months ago #1015 by Anna Z
Hello,

I'm trying to use Dirac and MRCC combination with help of dirac_mointegral_export utilite from MRCC package. I'm setting the symmetry in the Dirac .mol file. In the MINP file I usually set symm=off though it does not seem to affect the problem I'm explaining below.
If I use C2v symmetry for computations in Dirac then the computation in MRCC works perfectly.
However if I choose Cs symmetry (even for the same molecule), the reference determinant energy in MRCC is different from the total SCF energy in Dirac, and CC computation either converges badly or does not converge at all.
If I try to do the computations setting C1 symmetry in Dirac, MRCC fails immediately with the error "Check the inputfile for the no. g/u orbitals".
I suspect that the problem is that the reference determinant is transfered from Dirac to MRCC incorrectly. On the other hand, my colleague pointed out that two-electron integrals in Cs and C1 symmetry can be complex whereas MRCC assumes that they are real.
Is it possible to fix this problem by the appropriate change of MINP and fort.55 files? Or is it true that Dirac+MRCC combination can handle only molecular symmetries with real fermion irreps (i.e. D2h, D2, C2v)?

I attach Dirac out files and MRCC input and output files for Cs and C1 symmetries.