[CP2K-user] [CP2K:16818] OT Converges to excited state with IRAC?

Nicholas Winner nwinner at berkeley.edu
Wed Apr 6 18:02:09 UTC 2022

I ran a static calculation on a MoS2 monolayer using the following OT 

    algorithm irac
    rotation true
    preconditioner full_single_inverse
    energy_gap -1
    minimizer diis

I use these settings by default because, while full all and strict may 
result in faster convergence for some systems. Allowing for rotations in 
general is more robust in my experience. For the first time, however, an 
issue has come up when I ran the calculation it converged with a band gap 
of -1.66eV and a final energy of -3195.190101039151614 Ha.   On a hunch, I 
reran it using FULL_ALL and Algorithm strict and this gave a band gap of 
1.62eV and an energy of -3195.310508319606470 Ha. The energy difference is 
almost exactly two times the "correct" band gap so I looked at the MOs and 
found this 

   -0.05112749     -0.04139593     -0.04138555      0.02140865

 Fermi Energy [eV] :    0.582559

  Lowest Eigenvalues of the unoccupied subspace spin            1


 OT| Eigensolver reached convergence in 1 iterations

      -0.03958992      0.01966848      0.03075463      0.03075623

By the looks of it, the OT solver with IRAC converged to some kind of 
excited state. I have not seen this behavior before so I am wondering:

(1) Is this an expected consequence of not enforcing strict orthogonality?
(2) Is there something to do to fix the issue without giving up the ability 
to have Rotation True for fractional occupations?

I have attached the output file for the two calculations.


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