[Pw_forum] IFCs and Difference between unit cell and supercell
karan deep
karandeepster at gmail.com
Sat Oct 20 12:59:07 CEST 2012
> When I use supercell: simple cubic with 8 atoms to build silicon
> structure, the omega is different at gamma point with the omega from
> the structure with FCC.
This is same kind of question i asked about AFM material. sc is giving
8x3=24 modes of vibrations.
fcc gives 2x3=6 modes and these are different.
>in order to get exactly the same number, you have to use either
>a converged grid of k-points, or exactly the same k-points.
i try the example 2 of silicon which has 10 k-points mentioned in it for
both sc and fcc.
still vibrational modes are different. for sc it gives
Mode symmetry, T_d (-43m) point group:
omega( 1 - 3) = 9.5 [cm-1] --> T_2 G_15 P_4 I+R
omega( 4 - 6) = 140.4 [cm-1] --> T_1 G_25 P_5
omega( 7 - 9) = 140.7 [cm-1] --> T_2 G_15 P_4 I+R
omega( 10 - 12) = 408.2 [cm-1] --> A_1 G_1 P_1 R
omega( 10 - 12) = 408.2 [cm-1] --> E G_12 P_3 R
omega( 13 - 15) = 408.3 [cm-1] --> T_2 G_15 P_4 I+R
omega( 16 - 18) = 458.4 [cm-1] --> T_1 G_25 P_5
omega( 19 - 21) = 458.5 [cm-1] --> T_2 G_15 P_4 I+R
omega( 22 - 24) = 510.2 [cm-1] --> T_2 G_15 P_4 I+R
for fcc it gives
Mode symmetry, O_h (m-3m) point group:
omega( 1 - 3) = 3.2 [cm-1] --> T_1u G_15 G_4- I
omega( 4 - 6) = 510.2 [cm-1] --> T_2g G_25' G_5+ R
any suggestions please
Karandeep
Research Scholar
Physics Department,
IIT, Delhi
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20121020/d865ed81/attachment.html>
More information about the users
mailing list