[Pw_forum] Negative phonon frequency for 2D material of Sn (stanene)

[Yuma Nakamura]

Dear  Paolo



Thank you for your advice!

> -18 cm^-1 without Acoustic Sum Rule? it seems to me in an acceptable range
of values, not that big.

For matdyn.x run, I imposed asr = crystal (I also tried [asr = simple] but, result seems almost same).





>for instance:20 20 1 for k-points, 5 5 1 for phonon wavevectors

I tried this this suggestion.
 As you expect, I got much better result at Gamma point. 
However I got another negative frequency at another q-point. Is this still in an acceptable range even not in Gamma point especially for  calculating electron-phonon calculation?



     q = (    0.000000000   0.000000000   0.000000000 )

 **************************************************************************
     freq (    1) =      -0.171567 [THz] =      -5.722871 [cm-1]
     freq (    2) =      -0.171567 [THz] =      -5.722871 [cm-1]
     freq (    3) =       0.278781 [THz] =       9.299146 [cm-1]
     freq (    4) =       3.507583 [THz] =     117.000379 [cm-1]
     freq (    5) =       5.465255 [THz] =     182.301285 [cm-1]
     freq (    6) =       5.465255 [THz] =     182.301285 [cm-1]
 **************************************************************************


    q = (    0.200000000   0.346410162   0.000000000 )

 **************************************************************************
     freq (    1) =      -0.237381 [THz] =      -7.918166 [cm-1]
     freq (    2) =       1.182943 [THz] =      39.458728 [cm-1]
     freq (    3) =       1.276759 [THz] =      42.588083 [cm-1]
     freq (    4) =       3.284295 [THz] =     109.552288 [cm-1]
     freq (    5) =       4.845127 [THz] =     161.616026 [cm-1]
     freq (    6) =       5.169150 [THz] =     172.424283 [cm-1]
 **************************************************************************



=======q2r.x=======
&input
   fildyn='stanene.dyn', zasr='crystal', flfrc='stanene.551.fc'
 /


=======matdyn.x=======
 &input
    asr='simple',  amass(1)=118.710,
    flfrc='stanene.551.fc', flfrq='stanene.freq',la2F=.false., dos=.false., asr='crystal'
 /
151
   0 0 0 50
   

Yuma