[Q-e-developers] Strange problem in the calculation of monolayer InSe with QE

[Lorenzo Paulatto]

On Saturday, December 10, 2016 6:53:13 PM CET jinlong.ma.dr at szu.edu.cn wrote:
>    Then I try to find out the effect of polar part by removing the
> dielectric tensor, born charge and setting "T" to "F" in the IFCs.

Dear Jinlong,
I'm not sure that the procedure you used to remove the effective charges is the 
best one. Because if the EC are present in the dynamical matrix file at Gamma, 
they will be used to remove the long-range contribution from the dynamical 
matrices before transforming them to real-space force constants, if you then 
use these force constants to go back to G space, and the EC are missing, the 
phonon dispersion will miss it.

What you should do, is remove the effective charges (everything from 
"Dielectric constant") from the dyn mat file at Gamma (as I did in the attached 
file), then use these files to generate the real-space FCs with q2r.x and the 
resulting force constants with matdyn.x

BTW, in real 2D materials, long range interaction due to EC does not diverge, 
and EC should go to zero as you increase the inter-layer vacuum space. Hence 
it is perfectly safe to run ph.x with the option epsil=.false. to avoid 
computing the EC altogether.

HTH



-- 
Dr. Lorenzo Paulatto 
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
www:   http://www-int.impmc.upmc.fr/~paulatto/
mail:  23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05
-------------- next part --------------
Dynamical matrix file
                                                                           
  2    4  4  7.4242000  0.0000000  6.3635000  0.0000000  0.0000000  0.0000000
           1  'In  '    104650.204993143     
           2  'Se  '    71970.3716914906     
    1    1      0.5000000005      0.2886751343      3.5259887124
    2    1      0.5000000005      0.2886751343      2.8375112876
    3    2     -0.0000000005      0.5773502695      2.5131673962
    4    2     -0.0000000005      0.5773502695      3.8503326038

     Dynamical  Matrix in cartesian axes

     q = (    0.000000000   0.000000000   0.000000000 ) 

    1    1
  0.12342533  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.12342533  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000    0.26548255  0.00000000
    1    2
  0.00192207  0.00000000   -0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00192207  0.00000000    0.00000000  0.00000000
 -0.00000000  0.00000000   -0.00000000  0.00000000   -0.10739743  0.00000000
    1    3
 -0.00560449  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.00560449  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.00242423  0.00000000
    1    4
 -0.11978875  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.11978875  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.15616432  0.00000000
    2    1
  0.00192207  0.00000000   -0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00192207  0.00000000   -0.00000000  0.00000000
 -0.00000000  0.00000000   -0.00000000  0.00000000   -0.10739743  0.00000000
    2    2
  0.12342533  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.12342533  0.00000000   -0.00000000  0.00000000
  0.00000000  0.00000000   -0.00000000  0.00000000    0.26548255  0.00000000
    2    3
 -0.11978875  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.11978875  0.00000000   -0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.15616432  0.00000000
    2    4
 -0.00560449  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.00560449  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.00242423  0.00000000
    3    1
 -0.00560449  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.00560449  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.00242423  0.00000000
    3    2
 -0.11978875  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.11978875  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.15616432  0.00000000
    3    3
  0.12653201  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.12653201  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000    0.15876215  0.00000000
    3    4
 -0.00143905  0.00000000   -0.00000000  0.00000000    0.00000000  0.00000000
 -0.00000000  0.00000000   -0.00143905  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.00000000  0.00000000   -0.00023894  0.00000000
    4    1
 -0.11978875  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.11978875  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.15616432  0.00000000
    4    2
 -0.00560449  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000   -0.00560449  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000   -0.00242423  0.00000000
    4    3
 -0.00143905  0.00000000   -0.00000000  0.00000000    0.00000000  0.00000000
 -0.00000000  0.00000000   -0.00143905  0.00000000    0.00000000  0.00000000
 -0.00000000  0.00000000    0.00000000  0.00000000   -0.00023894  0.00000000
    4    4
  0.12653201  0.00000000    0.00000000  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.12653201  0.00000000    0.00000000  0.00000000
  0.00000000  0.00000000    0.00000000  0.00000000    0.15876215  0.00000000