[Pw_forum] Potential plot for SnSe

[Vahid Askarpour]

Let me share what I have found so far. I hope someone can at least verify if the following is correct:

1. in plot_1d routine of chdens.f90, the plotted x-axis is deltax*dble(i-1).
2. deltax = m1 / (nx - 1)
3. and m1 = sqrt (e1 (1)**2 + e1 (2)**2 + e1 (3)**2)

So in my case, m1, which is the modulus of e1=0.333 in alat units. That’s why the x-axis runs from 0 to ~0.33. However, the origin of the plot is (0,0,0) and not x0.

Thank you,

Vahid


On Jun 20, 2017, at 4:12 PM, Vahid Askarpour <vh261281 at dal.ca<mailto:vh261281 at dal.ca>> wrote:

Just a correction to my pp.x input file:

I actually used cartesian coordinates for the e1 and x0. So

0.3571863   0.2721583   0.1838386 for x0 and
0.1171583   0.2721583   0.1535005  for e1.

Vahid




        Feedback<http://aka.ms/SafetyTipsFeedback>
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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