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

[Mostafa Youssef]

Thank you very much for addressing my questions, Prof. Giannozzi ! I will keep 
the mailing list updated if I succeed in reasonably getting smearing work with 
finite electric fields.


Mostafa Youssef
MIT


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

[Paolo Giannozzi]

On Fri, May 22, 2015 at 9:51 AM, Mostafa Youssef  wrote:

 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?
>

the latter you said. Unfortunately there are many pieces of code on Berry
phases, electric fields, orbital magnetization, that have been written
having in mind spinless insulators with all bands filled only, and never
generalized. However, it seems to me, at a quick glance to
PW/src/bp_c_phase.f90, that you can compute Berry phases with smearing, as
long as the final result is insulating.

>
> (2) I recall Prof. Giannozzi in this mailing list mentioned that DFT+U is
> not tested with Berry phase calculations.
>

I don't remember anything about DFT+U and Berry phases, but I don't see any
obvious reasons why these two options shouldn't work together.

 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 field)) is the what PWscf
> prints as the total energy. I think it would be nice to designate this
> output  as the electric enthalpy especially that this will be consistent
> with what PWscf prints out for calculations under pressure.


I'll leave this point to people interested in calculations under electric
field

Paolo
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[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:

(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:

(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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