[Pw_forum] Single q-point calculation

Eyvaz Isaev eyvaz_isaev at yahoo.com
Sun Aug 15 11:37:10 CEST 2010


You can use options in ph.in file: start_q=5, last_q=5 to calculate phonons for 
particular q-point(s) from the mesh.
The result should not depend on the way how you got these dyn-files (supposing 
all parameters are the same and correct). 

The way you used is more convenient for a general q-point not presented in 

Prof. Eyvaz Isaev, 
Department of Physics, Chemistry, and Biology (IFM), Linkoping University, 

Theoretical Physics Department, Moscow State Institute of Steel & Alloys, 

isaev at ifm.liu.se, eyvaz_isaev at yahoo.com

From: Bipul Rakshit <bipulrr at gmail.com>

    Dynamical matrices for ( 6, 6, 1,)  uniform grid of q-points
     (   7q-points):
       N         xq(1)         xq(2)         xq(3)
       1   0.000000000   0.000000000   0.000000000
       2   0.000000000   0.192450090   0.000000000
       3   0.000000000   0.384900179   0.000000000
       4   0.000000000  -0.577350269   0.000000000
       5   0.166666667   0.288675135   0.000000000
       6   0.166666667   0.481125224   0.000000000
       7   0.333333333   0.577350269   0.000000000

in my output file.
I just want to ask, that is it wise to run the calculation usingldisp =true 
(graph.ph.in), which calculate the phonon frequencies one by one or 

Seven different calculations, using the above seven different q-points, using 
single q-point calculation (graph-singleq.ph.in)

Is both the ways gives final result same?

Because the latter method takes less time, than previous.


Bipul Rakshit
Research Fellow,
S N Bose Centre for Basic Sciences,
Salt Lake,
Kolkata 700 098

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