[Pw_forum] Potential plot for SnSe

[Vahid Askarpour]

Dear QE Users,

In order to calculate the total potential along one of the SnSe bonds (Se2-Sn4), I first performed a self-consistent run with the following lattice parameters.

ibrav=8, celldm(1)=21.34350847, celldm(2)=0.3628777, celldm(3)=0.38586894

Sn       0.882841736   0.250000000   0.602195343
Sn       0.617158264   0.750000000   0.102195343
Sn       0.382841736   0.250000000   0.897804657
Sn       0.117158264   0.750000000   0.397804657
Se       0.142813748   0.250000000   0.976427467
Se       0.357186252   0.750000000   0.476427467
Se       0.642813748   0.250000000   0.523572533
Se       0.857186252   0.750000000   0.023572533

I then ran pp.x with the following input:

&inputpp
    prefix  = 'SnSe'
    filplot = 'potential.dat'
    plot_num= 1
/
&plot
  iflag=1
  output_format=0
  nfile = 1
  filepp(1) = 'potential.dat'
  e1(1)=0.117158264,  e1(2)=0.750000000,  e1(3)= 0.397804657,
  x0(1)=0.357186252,  x0(2)= 0.750000000,  x0(3)=0.476427467,
  nx=100,
  fileout= 'VSe2_Sn4.dat’
/

The bond length is 2.73A=5.16Bohr. Attached is the output of potential vs. distance. The x-axis runs from 0 to ~0.33. According to other links in the Forum, the x-axis is in atomic units. Two possibilities:

1. The distance is in Bohr. So is the pp.x code plotting from 0 to 0.33 Bohr even though the bond length is 5.16Bohr as defined by the vectors x0 and e1?
2. The distance is in alat. Then 0.33*alat=7.04Bohr. This is longer than the bond length.

So what is the unit of the x-axis?

Thank you,

Vahid

Vahid Askarpour
Department of Physics and Atmospheric Science
Dalhousie University,
Halifax, NS, Canada




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