[Pw_forum] A question about PSP Ti.pbe-mt_fhi.UPF and a general question about DFT+U in QE

[Hanghui Chen]

To whom it may concern,
    I noticed an anomaly with the psp Ti.pbe-mt_fhi.UPF in the library. Its
valence configuration reads as:

    nl pn  l   occ       Rcut    Rcut US       E pseu
    4s  4  0  2.00      0.000      0.000     0.000000
    4p  4  1  2.00      0.000      0.000     0.000000
    3d  3  2  0.00      0.000      0.000     0.000000
    4f  4  3  0.00      0.000      0.000     0.000000

 I personally think the occupancy for 4p and 3d are incorrect. The
correct occupancy might be 4p: 0.00 and 3d: 2.00. I am not sure
whether this is indeed the correct psp or a bug in the psp. I want to
double check with the community, since it is a psp converted from the
Abinit web site.

   A related question to this problem is that in the current
implementation of DFT+U in QE, the occupancy for the 'correlated
orbital' must have an occupancy larger than 0. Therefore for this psp
of Ti, I can not turn on U on its d orbital. I am just curious, is
"occupancy of the correlated orbital > 0" a strict condition? Can we
make it "occupancy of the correlated orbital >= 0"? I manually changed
the source code and it seems that there is no major difference as I
have observed.

  Thank you very much for your time.
  Best regards.

Hanghui Chen
Assistant Professor of Physics
New York University Shanghai
Email: hanghui.chen at nyu.edu
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