[Wien] I2/a to b2/b space group

[E.A.Moore]

LDA is known to underestimate band gaps. However have you checked that the internuclear distances are the same for your two structures? The a value for b2/b is a lot larger than the c value for the I2/a structure. 
You could try using P1 and entering all the atoms in the unit cell and see what symmetry WIEN2k picks up.
Or put the space group number which is the same for I2/a and C2/c.
 
You don't get exactly the same results for the same unit cell described by different space groups but I doubt if it makes a difference of 0.7 eV in the band gap.
 
 
Dr. E. A. Moore
Reader in Theoretical Chemistry
Department of Chemistry and Analytical Sciences
The Open University
 
 

________________________________

From: wien-bounces at zeus.theochem.tuwien.ac.at on behalf of ali hamidani
Sent: Tue 24/03/2009 17:00
To: wien at zeus.theochem.tuwien.ac.at
Subject: [Wien] I2/a to b2/b space group



Dir all 

I have used an external program to convert the I2/a to b2/b space group for monoclinic compound (I think I2/a space group no yet implemented in wien2k).

My question is: are the both structures gave the same properties; because I have found the lattice parameter is changed and I think the electronic properties affected by this parameter. In another hand I have found the band gap is 0 eV, in contrast with the experimental 0.7 eV. Is this due to the change of structure or from the approximation used (LDA) 

Initial unit cell: (I2/a)


6.2070 5.8570 5.8740 90.000 111.800 90.000

Final unit cell: (b2/b)


6.7787 6.2070 5.8570 90.000 90.000 126.430

   

Ali Hamidani

Physics Laboratory at Guelma

University 08 Mai 1945

P.O. 401Guelma 24000

Algeria

---------------------------------
The Open University is incorporated by Royal Charter (RC 000391), an exempt charity in England & Wales and a charity registered in Scotland (SC 038302).
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/ms-tnef
Size: 5424 bytes
Desc: not available
Url : http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20090324/b5682345/attachment.bin