I am completely new to material modelling. I am trying to calculate phonon frequency at X point for Aluminium fcc.

I picked an fcc lattice and displaced the atoms at x=0 by (+0.1) and those in x=0.5 by (-0.1) along the z direction. I calculate energy for different values and try to fit a quadratic curve on it. This allows to measure $k$ so that: $$\omega = \sqrt{\frac{k}{2m}}$$ Because I have two atoms. The results I find are completely wrong.

Here is my code:

    tstress = .false.
    tprnfor = .false.
   ibrav = 2
   celldm(1) = 7.631664 
   nat = 2
   ntyp = 1
   ecutwfc = 40
   ecutrho = 160

    conv_thr = 1.0e-10
  Al   26.98100  Al.pbe-n-kjpaw_psl.1.0.0.UPF
Al   0.000000000000000   0.000000000000000   0.0100000000000
Al   0.500000000000000   0.500000000000000   -0.0100000000000

Thank you very much for you help


1 Answer 1


ibrav=2 means that your lattice is fcc, i.e. if you put an Al atom at (0,0,0) , then three Al atoms are put at (1/2,1/2,0), (1/2,0,1/2), (0,1/2,1/2) automatically. Thus your input means that Al1 is at (1/2,1/2,0.01) and Al2 is at (1/2,1/2,-0.01). It may cause CRASH.

For your purpose I recommend to see UserGuide and to perform ph.x with single k-point mode.

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