[CP2K-user] OT produces negative gap for 1eV gapped semiconductor?

[Nicholas Winner]

Hello everyone. I have a semiconductor, BeSiP2, which has a band gap 
slightly above 1eV in the GGA approximation 
(https://materialsproject.org/materials/mp-1009085/).

I calculate a vacancy, V_{P}^{+3}, first using diagonalization. Which 
produces a band gap around 1eV, indicating that the charge does not 
delocalize, and so OT should still be appropriate. When I switch to OT, 
however, there is a negative homo/lumo gap and I can see it in the 
eigenvalues:

0.17131297      0.17154145      0.18362819      0.18519005

 Fermi Energy [eV] :    5.039278

  Lowest Eigenvalues of the unoccupied subspace spin            1

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

  Reached convergence in            1  iterations

       0.18499549      0.22295666      0.23850766      0.25228060


This is bizarre to me. OT is usually very reliable for me. So this is a 
strange inconsistency, and maybe its due to how I'm running the 
calculation. For OT I use the full_all preconditioner, and the rest 
defaults. For diagonalization I the section at the bottom. Anyone have any 
guesses as to why there is this discrepancy? 

-Nick

&SCF

    MAX_SCF 200

    added_mos 100

    eps_scf 1e-6

    max_diis 15

    &diagonalization

    &end

    &mixing

    &end

    &smear

        elec_temp 300

        method fermi_dirac 

    &end

&end
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