[Pw_forum] Finite electric field (smearing , DFT+U, and total energy)

[Mostafa Youssef]

Dear PWscf users and developers,

I have 2 questions and a comment on finite electric field calculations in PWscf and your help and thoughts are very appreciated.


Questions:
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(1)  PWscf refuses smearing in Berry phase calculations (lelfield=.true.). However, smearing could help in accelerating the convergence of some in-gap states for semiconductors that arise because of a defect or impurity. Is there a fundamental reason for why smearing should not be used with Berry phase calculations, or is it possible to modify PWscf to accept smearing?


(2) I recall Prof. Giannozzi in this mailing list mentioned that DFT+U is not tested with Berry phase calculations. The code does not complain about DFT+U with Berry phase and I have performed preliminary tests on metal oxides and found out that dielectric constant predicted using DFT+U and (lelfield=.true.) are reasonable compared to results obtained with other codes using DFTP(+U).  I wonder if somebody did more tests on DFT+U with Berry phase and would like to share their conclusion.


Comment:
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(3)  The total energies that PWscf outputs in finite electric field calculations are in fact electric enthalpies.  One could check that the ( Harris-Foulkes estimate   +  (total dipole x filed)) is the what PWscf prints as the total energy. I think it would be nice to designate this output as the electric enthalpy espeically that this will be consistent with what PWscf prints out for calculations under pressure. (Of course with the implicit warning that the enthalpy inherits the uncertainty in the polarization quantum).


Thank you,
Mostafa Youssef
MIT


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