Automatic k-point generation

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Joined: Fri Feb 01, 2019 7:53 am

Automatic k-point generation

Post by AntonF » Fri Feb 01, 2019 8:18 am

Dear all,
I am new to Abinit and just try to perform some GS-calculations for different systems, but get stuck with k-point grid symmetry.
Suppose I'm taking the AlAs system from the RF2 tutorial. When I run the code with the following option

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ngkpt   6  6  6          
nshiftk   4              # Use one copy of grid only (default)
shiftk   0.0 0.0 0.5    # This gives the usual fcc Monkhorst-Pack grid
 0.0 0.5 0.0
 0.5 0.0 0.0
0.5 0.5 0.5

everything is OK, but when I try to remove the shifting options, i.e. leave just

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ngkpt   6  6  6   

the code complains that

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Chksymbreak=1 . It has been observed that the k point grid is not symmetric :
    for the symmetry number    2
    with symrec=  0  0  1 -1 -1 -1  1  0  0
    the symmetric of the k point number    512 with components   -6.250000E-02   -6.250000E-02   -6.250000E-02
    does not belong to the k point grid.
    Read the description of the input variable chksymbreak,
    You might switch it to zero, or change your k point grid to one that is symmetric.

I don't quite get this as e.g. in Elk code we have a similar parameter ngridk, which can be set to any value without need to set the shifts (or may be Elk does it automatically?). In other words, what should I do in a general case if I have some structure and I don't know how to set the shift options correctly and I just want to control the number of grid points for K points generation? Can Abinit solve out these symmetry issues automatically?

Thank you in advance,
Anton F.

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