[Pw_forum] Finite electric field calculation

[alan chen]

Dear PWSCF users,
     I have two questions about finite electric field calculation based on
Berry phase.
     First, I have found in the source code that the formula to calcuate the
polarization in the presence of finite electric field is different in
Version 4.0 from in Version 3.2. A couple of factors like sqrt(2) and alat
are added in the new version. I just want to make sure that if I use
ultrasoft psedupotential and turn on finite electric field, does the latest
version (4.0) of PWSCF calculate the polarization and atomic force
correctly? No offense intended.
     Second, is there a range of electric field in which the Berry phase
method works? In the example31 the electric field is 0.001 a.u. I want to
calculate some properties under the electric field as large as 0.01 a.u. In
principle I think the method works for any value of electric field but in
practice any restriction on the maximum of electric field?
     Thank you very much.

Hanghui Chen
Department of Physics
Yale University
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