Dear Wien2k users,
I have calculated NMR chemical shifts for several crystals and I have
not had any problem but in the case of graphite something is going
wrong. The chemical shift it is not converging with the number of k
points. The value of the chemical shift goes up and down and in some
cases it just explode. For example: with 33 x 33 x 10 k points the
values is 4896 ppm while with 26 x 26 x 8 k points the value is 44 ppm
what it is closer to the expected value.
I had used 120000 (72 x 72 x 22) k points and it still not converge.
I had notice that depending in the number of k points some times it
converge to a insulator configuration and sometimes to a metallic one.
When it converge to an insulator configuration the chemical shift is
closer to the experimental value.
I am using PBE functional but I have also try PBEsol and TPSS without
success.
Any idea in what could be the problem?
Thanks
kind regards
Jose
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