Nonzero Fermi-contact hyperfine field in insulators

[imazin2]

I set LHYPERFINE to true, and, to my surprise, I got a huge (~40 T) hyperfine Fermi-contact field despite my material being a semiconductor with a 1 eV gap. I am using tetrahedrons, so no "leaking" due to finite temperature.
I think this is because VASP places the Fermi level exactly at the top of the valence band, so the calculation is picking some spurious electron density from the valence band. A simple solution would be to add another parameter like SHYPERFINE = shift of the Fermi energy to apply before the hyperfine field calculations. Adding SHYPERFINE = 0.5 would likely solve the problem.

[zahedzx]

Hi,

Can you provide a minimal reproducing example? (check below link for more details)
https://www.vasp.at/wiki/index.php/Mini ... le_example

For an insulating system with fixed occupations, shifting the Fermi level within the gap would not normally be expected to change occupied-state quantities, so it would be useful to verify whether the large contact field originates from the electronic structure itself or from the hyperfine implementation.

Best regards,
Zahed

[imazin2]

Thank you. Let me collect more information and get back to you with a clean question.