[Pw_forum] Question about induced dipole moment

[lan haiping]

Thank you very much , Prof Marzari .
Why can we safely treat metallic nanotubes with wfs' centers change  ?
Just because of its feature DOS pattern at Fermi level ？

With Regards，
Hai-Ping


On 9/19/07, Nicola Marzari <marzari at mit.edu> wrote:
>
> lan haiping wrote:
> > Dear Stefano,
> > i notice such problem, but in Prof Marzari's work on cnt, the transverse
> > polarizabilities of metallic nanotubes are given.  My confusion may be
> > due to this example.
> > Thank you
> >
> > Regards
> > Hai-Ping
>
>
> Dear Hai-Ping,
>
> 1) the transverse polarizabilities are finite for both metallic
> and insulating nanotubes. It's the longitudinal one that is
> infinite in metallic tubes. Note that 3n,0 tubes at small diameters
> are semiconducting with small gaps.
>
> 2) as mentioned, we did calculate them in real space from the integral
> of the charge density. This is an appropriate operation for a finite,
> isolated system - in the transverse direction this is what they are.
>
> 3) re. electric enthalpy - not sure what the status of that is.
> I'll try to discuss it when Paolo Umari visits later in October.
>
> 4) you could use WFs - both for truly semiconducting nanotubes,
> and even for the worse case scenario of (n,n) armchair (metallic)
> ones. Treat the system as insulating, and you should
> find a solution with WFs that corresponds to covalent bonds,
> and 1 p_z-like WF every 2  carbons. The center displacement as a
> function of field gives you the polarizaton.
>
> Best,
>
>                         nicola
>
>
> ---------------------------------------------------------------------
> 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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