[Pw_forum] RE: Pw_forum digest, Vol 1 #668 - 2 msgs

[Eyvaz Isaev]

**************************************************************************
> omega( 1) =   1.154106 [THz] =   38.497100 [cm-1]
> omega( 2) =   1.154106 [THz] =   38.497100 [cm-1]
> omega( 3) =   1.154106 [THz] =   38.497100 [cm-1]
> omega( 4) =  33.423461 [THz] = 1114.894068 [cm-1]
> omega( 5) =  33.423461 [THz] = 1114.894068 [cm-1]
> omega( 6) =  33.423461 [THz] = 1114.894068 [cm-1]
>
**************************************************************************
> but as we know, the exact frequencies should at
> about 1055 and 1305 cm-1
> 
> I'm not sure whether pw.x+ph.x can get the LO/TO
> splitting, and the whether 
> this 38.497 cm-1 is TO mode?
> 
> I have change the cut of energy and the k-point
> sampling to 5*5*5, but the result is not change
much!

Hi, 

In order to get LO/TO splitting for the Gamma point
you should calculate the phonon spectrum for \Gamma-A
(or \Gamma-M) direction, in your particular case,
using matdyn.x. This means that you have to calculate
force constatns for a given q-points mesh, including
the \Gamma-point. 

By the way, this is explained in example6. See your
pw_examples directory.

Bests,
Eyvaz.



	
		
__________________________________ 
Do you Yahoo!? 
Yahoo! Mail - You care about security. So do we. 
http://promotions.yahoo.com/new_mail