[Pw_forum] Negative starting charge for Zr USPP

[Mostafa Youssef]

Dear all,

When I use an USPP for Zr that contains nonlinear core corrections to study ZrO2, I always get negative starting charge. For example, I see the following 3 lines:

Check: negative/imaginary core charge=   -0.000004    0.000000
Check: negative starting charge=   -0.238895
 negative rho (up, down):  2.389E-01 0.000E+00

I tried to increase the energy cutoff to 85 Ry and charge density cutoff to 850 Ry but this has no effect at all.

However, if I use an USPP for Zr that does not have nonlinear core corrections, this negative charge does not show up in the output file.

In the FAQ, it says that one should worry if this negative charge is 0.001x no. of electrons, in the case of Zr it is about 0.002 x no. of electrons.

Any suggestions on how to avoid this negative charge while retaining nonlinear core corrections.

Thank you
Mostafa Youssef
Postdoctoral Associate
MIT
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