[Pw_forum] Question about induced dipole moment

[degironc]

the static dielectric constant of a metal is infinit.... 
what are you trying to calculate ?
stefano

lan haiping wrote:
> Thank you, Prof Marzari.
>
> As far as i know, the changes of the WFs' centers can be applied to 
> insulating systems.
> While for metallic or semi-metallic systems, Is such scheme still 
> useful ?  in fact, i still  donot know how to define the wfs' centers 
> for metallic systems.
>  
> i found it is hard to achieve convergence when i applied  
> electric-enthalpy approache to
> metallic systems no matter which direction of the uniform electric 
> field involves.
> i do notice the difficulties of scf convergence  of systems under 
> electric field.  i tried to
> reduce mixing parameter , or increase the smearing width, but no 
> success.   Are there
> any other parameters i should pay attention to ?
>
> With Regards,
> Hai-Ping
>
>
> On 9/19/07, *Nicola Marzari* <marzari at mit.edu 
> <mailto:marzari at mit.edu>> wrote:
>
>
>
>     Dear Hai-Ping,
>
>     it was done directly with real space integration - i.e. in the
>     transferse direction, the dipole is given by the integral of r rho(r).
>
>     It could also be done by looking at the change in position of the
>     sum of the centers of the Wannier functions - this is less accurate,
>     since the reciprocal-space expression for the position operator is
>     based on a finite-differences discretization.
>
>
>                                     nicols
>
>
>     lan haiping wrote:
>     > Hi,   All.
>     >     I have read a work of  Prof Marzari  performed by QE package to
>     > compute static dielectric properties of nanotube systems : PRL
>     96, 166801.
>     >      To extract dielectric quantities, there are 2 methods
>     mentioned in
>     > this work. I have a question about the method adopted by the
>     sawtooth
>     > potential . In order to obtain transverse polarizability , we
>     need know
>     > the  dipole moment induced by external sawtooth potential .  I
>     have done
>     > several tests on similar systems carbon nanotube (6,0), but i
>     have not
>     > found how to extract such induced dipole moment .
>     >  Would anyone please give me a hand on this subject  ?    Any
>     tips or
>     > references  are appreciated !
>     >
>     >    Best wishes
>     >     Hai-Ping
>     >
>
>     --
>     ---------------------------------------------------------------------
>     Prof Nicola Marzari   Department of Materials Science and Engineering
>     13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
>     tel 617.4522758 fax 2586534 marzari at mit.edu
>     <mailto:marzari at mit.edu> http://quasiamore.mit.edu
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>
>
> -- 
> Hai-Ping Lan
> Department of Electronics ,
> Peking University , Bejing, 100871
> lanhaiping at gmail.com <mailto:lanhaiping at gmail.com>, hplan at pku.edu.cn 
> <mailto:hplan at pku.edu.cn>
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