# [Pw_forum] k point value

mohnish pandey mohnish.iitk at gmail.com
Fri Nov 18 07:32:36 CET 2011

```Dear Padmaja,

These k-values are the k-points in high symmetry direction which you choose
to plot the band structure. Automatic grid generated for "scf" calculation
if often not suitable for band-structure plot so we choose a high symmetry
direction and discretize the reciprocal space in that direction. These are
called special k-points for band structure plot. You can write a small code
to generate a mesh with given high symmetry special k-points. And regarding
the answer to your second question the unit of the total energy is always
in Ryd. Its not a very big issue to figure out. Generally the fermi energy
and in few more cases the energy could be in eV. Hope this helps.

On Thu, Nov 17, 2011 at 11:17 PM, Padmaja Patnaik <

> Dear all
> I am using QE since last few yeras but still could not answer few
> questions a new student in my lab asked me. When we are doing band plot its
> a curve between k~E.  In the input file we give ka values as,
>
>    0.0  0.0  0.0
>    0.0  0.0  0.1
>    0.0  0.0  0.2
>    0.0  0.0  0.3
>    0.0  0.0  0.4
>
> then what how are we getting the k values to plot the band structure. The
> values in the data file looks different from these values.
>
> Another question is, which unit is followed in QE?
> a.u. (hbar = e^2 = m_e = 1, energy  in Hartree)  or Rydberg unit ( hbar=1,
> e^2=2, m_e=1/2, energy in rydberg).
>
> Sometimes the output energy is given in eV and sometimes in Rydberg. This
> is confusing that which unit is followed in QE.
>
> please suggest on these two points.
> Regards
>
> Research Scholar
> Dept of Physics
> IIT Bombay
> Mumbai, India
>
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>
>

--
Regards,
MOHNISH,
-----------------------------------------------------------------
Mohnish Pandey
BTech-Mtech, IIT Kanpur
Senior Project Associate,
Department of Chemical Engineering,
IIT KANPUR, UP, INDIA
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