The ABINIT Users Mailing List ( CLOSED )

[paul.boulanger@umontreal.ca]

Hi,

this is the result of the band gap underestimation of the LDA (or GGA) 
approximation to the exchange-correlation energy. It is well documented and 
is a recognized flaw of the Kohn-Sham formalism. After all, the Kohn-Sham 
band structure is not really the physical one particle band structure. To 
correct the band gap, one needs to apply GW corrections (which can be done 
with Abinit, see tutorial: 
http://www.abinit.org/Infos_v5.2/tutorial/lesson_gw.html).

If you want to further your comprehension of the different formalisms used in 
modern Ab Initio calculations, I strongly recommend Richard Martin's book: 

Electronic Structure: Basic Theory and Practical Methods
Cambridge University Press, New York, 2004
ISBN 0 521 78285 6

A final note, you should always compare the results of youre calculation to 
0K experimental results since all calculations (maybe not if your use some 
electronic temperature) are done at this temperature. In your case, you 
should compare to a band gap of 1.17 eV for Si, not 1.12 eV.

Paul