[Pw_forum] Question about induced dipole moment

[lan haiping]

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> 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 http://quasiamore.mit.edu
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-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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