[QE-developers] Problem of the momentum matrix element at the Gamma point

[Paolo Giannozzi]

The nonlocal contribution involves derivatives of j_l(kr). I vaguely
remember that the limit k=0 is tricky, but I was convinced that it had been
properly implemented many years ago

Paolo

On Sat, May 16, 2020 at 8:12 AM L Y <xifntx at gmail.com> wrote:

> Dear Quantum ESPRESSO developers,
>
> My question was posted initially to the user mail list, and I already
> obtained help from Dr. Iurii. It is abit technical, so I formulate it here
> again to see if anyone has ideas or suggestions. I think it could be a bug.
>
> I calculated the the momentum matrix element between the valence and
> conduction bands in MgO, along a k-path going through the Gamma point. At
> the Gamma point, there is a clear discontinuity, see attachment
> "p_with_nonlocal.png" (Gamma point at ik=31), while the band energies are
> all continuous. I tried many different types of pseudopotentials (norm
> conserving, ultrasoft, PAW) and functionals (LDA, PBE), all showing this
> discontinuity, (although the SG15 ONCV pseudopotentials seem to be better).
>
> When I commented out the part in "compute_ppsi.f90" involving the
> non-local pseudopotential, the discontinuity is gone, see attached
> "p_without_nonlocal.png". This leads me to believe that there is
> potentially a bug in the calculation of the commutator i [r, V_nl] for the
> Gamma point. I was wondering whether anyone has ideas or suggestions on why
> this occurs and where in the code I should look at to try to find the
> potential "bug".
>
> Sorry for the long mail.
> Best regards,
> Lun Yue
> Louisiana State University
> _______________________________________________
> developers mailing list
> developers at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/developers
>


-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/developers/attachments/20200516/53b03f21/attachment.html>