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Posted: **Thu Sep 21, 2023 1:26 am**

Dear VASP admin,

When I used KPOINTS mesh:

Automatic
 0
Gamma
 1  3  3
 0. 0. 0.

The output IBZKPT file shows with vasp5:

Code: Select all

Automatically generated mesh
       4
Reciprocal lattice
    0.00000000000000    0.00000000000000    0.00000000000000             1
    0.00000000000000    0.33333333333333    0.00000000000000             2
    0.00000000000000    0.00000000000000    0.33333333333333             2
    0.00000000000000    0.33333333333333    0.33333333333333             4

But with VASP6:

Code: Select all

Automatically generated mesh
       4
Reciprocal lattice
    0.00000000000000    0.00000000000000    0.00000000000000             1
    0.00000000000000    0.33333333333334    0.00000000000000             2
    0.00000000000000    0.00000000000000    0.33333333333333             2
    0.00000000000000    0.33333333333334    0.33333333333333             4

and on another server with VASP6:

Code: Select all

Automatically generated mesh
       4
Reciprocal lattice
    0.00000000000000    0.00000000000000    0.00000000000000             1
    0.00000000000000    0.33333333333334    0.00000000000000             2
    0.00000000000000    0.00000000000000    0.33333333333334             2
    0.00000000000000    0.33333333333334    0.33333333333334             4

Why such numerical changes at the last digit, I suppose it should be the same as vasp5? Should I worry about that?

Thanks

Posted: **Thu Sep 21, 2023 6:58 am**

Dear Ibrahim,

the changes in the last digit are numerical noise which always occur in floating point calculations.
There is no need to worry about that.
In fact, vasp uses SELECTED_REAL_KIND(p=10) for most calculations, which essentially means the code runs the calculations with a decimal precision of 10 digits.

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IBZKPT file

IBZKPT file

Re: IBZKPT file