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### Ypp for 2D system

Posted: Fri Apr 27, 2018 3:43 pm
Dear all,
I need to generate the random q ponit using Ypp for the 2D system, after the ypp -k r, I have got the list of the q points as：
# c1 c2 c3
0.2410658 -0.1169918 0.0150385
-0.2986234 -0.2476754 0.0421619
0.2558869 0.4675771 0.0195998
-0.2407992 0.5680680 -0.0385039
0.4058249 0.1226135 -0.0255852
0.1039617 -0.0368117 -0.0503623
0.6114251 -0.0102372 -0.0135034
0.4017547 0.3906757 0.0053636
...
...
My questions is why the 2 demensional system has the q point in the c3 (vaccum in my system along z direction) ? If I use the output random points to calculate the electron-phonon interaction, are this generated points reasonable? (I think the c3 direction should be all zero)

Thanks!

Shudong

### Re: Ypp for 2D system

Posted: Wed May 02, 2018 8:52 am
Dear Wang,
by default ypp generates random k-points in 3D.
I think you just need to replace the numbers in the third column with a series of zeros.
However I suggest to plot the result, to be sure that the k-points are reasonably random also in 2D.

Best,
D.

### Re: Ypp for 2D system

Posted: Wed May 02, 2018 10:39 am
There exits an example about ypp executable http://www.yambo-code.org/input_file/ypp/ypp_kk.phpshown how to
generate the k point. The output are
.....
<---> User K-points : 1
<---> Reducing & Expanding the 12 k-points ...done
<---> Reduced K-grid points: 12
---------- Reduced K-grid ----------
0.0000000 0.0000000 0.0000000 0.0085470
0.3333333 0.0000000 0.0000000 0.0512821
0.3333333 0.3333333 0.0000000 0.0170940
-0.2333333 0.1999999 0.0000000 0.1025641
0.1000001 -0.4666667 0.0000000 0.1025641
0.4333333 -0.1333333 0.0000000 0.1025641
-0.5666667 0.2000001 0.0000000 0.1025641
0.0999999 -0.1333333 0.0000000 0.1025641
-0.2333333 0.5333334 0.0000000 0.1025641
-0.2333333 -0.1333335 0.0000000 0.1025641
0.4333334 -0.4666666 0.0000000 0.1025641
0.1000000 0.2000000 0.0000000 0.1025641 1

Does the zeros have been generated as your suggestion? (e.g. replace the c3 component with zeros)

Thanks!

Shudong

### Re: Ypp for 2D system

Posted: Thu May 03, 2018 12:40 am
That was generated with ypp -k k which properly detects the grid dimension, since it needs to create another regular grid.
Instead you want random k-points, i.e. ypp -k r, which is a different run.

Best,
D.