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Fermi energy and work function

Posted: Sat Apr 14, 2007 4:52 pm
by user
Dear All,

Work function is defined as: \Phi=E(vacuum)-E(Fermi); in VASP calculations, E(Fermi) is set at the top of the valence band, which can be found in OUTCAR.

For metals, it is straightforward to calculate \Phi using E(Fermi) from OUTCAR.

My question is: in semiconductors, how do we define E(Fermi) for the work function? should we instead take it at the middle of the band gap?

Thanks.

Fermi energy and work function

Posted: Mon Apr 16, 2007 12:42 pm
by admin
experimentalists usually define it as the middle of the band gap. However, by standard DFT calculations the band gap usually is under-estimated, therefore E-fermi is usually calculated from the hightest occupied eigenvalue in DFT calculations.

Fermi energy and work function

Posted: Wed Apr 25, 2007 7:17 am
by lcyin
How can we obtain the E(vacuum), does the E(vacuum) equal to zero?

Fermi energy and work function

Posted: Wed Apr 25, 2007 4:59 pm
by user
Nope. You have to get E(vacuum) from the averaged electrostatic potential, see Hand-ons III: http://cms.mpi.univie.ac.at/vasp-worksh ... tation.htm

Fermi energy and work function

Posted: Thu Apr 26, 2007 1:52 am
by lcyin
Thanks!

Fermi energy and work function

Posted: Thu Apr 26, 2007 7:11 am
by lcyin
But I have not the vtotav utility in hand
Can Admin. or other vasp user send it to me?
Thank you.