[Pw_forum] finite electric fields

[li niu]

Dear Paolo U,
   
  Thanks for your reply. I'm very interested for your finite electric field method.
The dielectric polarizability tensor can be calculated by taking dinite differences of  atomic forces.
I have several questions to ask you.
   
  1. We obtained the diagonal terms, by considering values for the electric field of
-2h,-h, 0, h and 2h in the cp.x code [tefield=.true. 
                                                        tcg = .true.,
                                                      epol = 1 or 2 or 3
                                                     efield = -2h,-h, 0, h or 2h],
and by using the five-point formular . Is it right?
   
  2. For the calculation of the off-diagonal terms, two different electric fields 
are required. This need apply electric fields of intensity -2h/1.414,-h/1.414, 
0, h/1.414 and 2h/1.414 along the three different couples of cartesian directions, and apply eauation.
But how can I apply simultaneously finite fields along two different Cartesian directions
in cp.x code?[ESSPRESSO-3.2]
 
3. In this way, we could obtain all the dielectric polarizability tensor. Then the
Raman susceptibilities associated to the normal mode n can be obtianed according to the equation. 
How to implement it ? By a small code?
   
  Best!
   
  I'm counting on the new version.
   
  Niu Li

       
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