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Dear VASP users,

I have a question regarding the different electronic smearing options in VASP:
when using Fermi smearing (ISMEAR = -1), to what quantity is the smearing (SIGMA) applied?
To be more specific: the Methfessel Paxton prescribes a smearing corresponding to the approximation of delta functions in energy delta(E-E_k) by functions with finite smearing widths. This induces a smearing of features in the electronic DOS.

What I wonder, regarding the Fermi smearing option in VASP, is whether the energy levels are similarly broadened in energy (as in a MP scheme of order zero), or wether it is just the _occupation numbers_ that follow the Fermi distribution?
The section of the manual on ISMEAR did not answer my question precisely, hence the post.

Since I get smoother electronic DOS curves with VASP upon increasing SIGMA (when using Fermi smearing, ISMEAR=-1) for a fixed CHGCAR, it seems to me that the energy levels are indeed broadened (by the derivative of the Fermi function?). Is this correct?

Thanks for your help.

Olivier

you are right, the smearing (SIGMA) is applied to broaden the energy levels (KS-eigenvalues) themselves.

To clarify this further: what is the functional form of the Broadening for the KS-eigenvalues in this case (ISMEAR = -1) ?
Is it the energy derivative of the Fermi function?

Thanks in advance.

Also, in the case of ISMEAR=-1, is SIGMA the value of k*Tel,
or is it defining some other measure of the width of the derivative of the Fermi-Dirac function?