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I have a question about the Fermi energy. The Fermi energy given by the VASP is not correct. Could anyone let me know how to estimate the real fermi energy from OUTCAR or elsewhere? Is there any correction I should use to get the correct value? Thanks.

What do you mean by "the Fermi energy is not correct"? While the Fermi energy obviously depends on the smearing you use, it is defined such that the sum over all occupied states times the corresponding weight equals to the number of electrons.

You know, the Fermi energy calculated by VASP is positive (the number given by DOSCAR), but the correct value should be negative at 0K. So, I wanna know if there is any way to estimate the correct Fermi energy.

Absolute eigenvalues of DFT are not really meaningful and by extension that is also true for the absolute value of the Fermi energy. The more interesting quantities for almost all applications is the relative value of the eigenvalues. For which application would you even need the absolute value of the Fermi energy?