add alpha+bet to get absolut eigen values (Band offset)

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jdasilva · #1 Post by **jdasilva** » Sat Nov 04, 2006 4:33 am

After the Fermi energy in OUTCAR there is the sentence
"add alpha+bet to get absolute eigenvalues".

Did you someone calculate absolute eigenvalues using this procedure and from that obtained the band offset between two semiconductors??

Bye
Juarez

#2 Post by **admin** » Tue Nov 14, 2006 2:34 pm

please be aware that it is an approximation to use alpha+bet as the energy offset. If possible (for slab systems or any other system which contains a vacuum region), please use the LVTOT=True option, and plot the panar average of the potential (file LOCPOT). If the vacuum region is large enough, the potential will reach its constant value in the vacuum, which is a better estimate of the
E-zero of the system.

jdasilva · #3 Post by **jdasilva** » Tue Nov 14, 2006 7:23 pm

Thanks for the comment:
(1) How do you calculate ALPHA+BET?
(2) What approximation is used to obtain ALPHA+BET?

We calculated BAND OFFSET for semiconductors using 3 approaches and we know the difference between the wrong the correct results.

In one of the approaches, we used alpha+bet. The results are not bad, however, What does ALPHA+BET mean? How does VASP calculate it??

Thanks in advance
Juarez