[DFTB-Plus-User] Applying an electric field with periodic boundaries

[Ashwin Ramasubramaniam]

Thanks, Ben. This is exactly what I need.

best regards,
-Ashwin.


Message: 2
> Date: Fri, 06 Aug 2010 15:48:51 +0100
> From: Ben Hourahine <benjamin.hourahine at strath.ac.uk>
> Subject: Re: [DFTB-Plus-User] Applying an electric field with   periodic
>        boundaries
> To: User list for DFTB+ related questions
>        <dftb-plus-user at dftb-plus.info>
> Message-ID: <4C5C20D3.7030708 at strath.ac.uk>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hello Ashwin,
>
> you need to use something like:
>
> Hamiltonian = DFTB {
>  SCC = Yes
>  ElectricField = {
>    PointCharges = {
>      CoordsAndCharges [AA] = {
>        0.0 0.0  100.0  1.0 # Charge +1 at 100AA above layer
>        0.0 0.0 -100.0 -1.0 # Charge -1 at 100AA below
>      }
>    }
>  }
>
> with the z direction of the supercell being large and the layer at z=0.
>
> However, in the special case of a 2D graphene layer perpendicular to the
> field the all of the atoms are at the same height, so experience the
> same potential. The contribution added to the Hamiltonian in this form
> of tight binding is proportional to the difference in potential between
> atomic sites, so depending on which gauge is used the band structure
> will shift up and down but not change. Similarly the gauge independent
> energy won't change.
>
> Regards
>
> Ben
>
> Ashwin Ramasubramaniam wrote:
> > Hello Ben,
> >
> > Thanks for your reply. I have a sheet of graphene which is periodic in x
> > and y (and a large periodic distance in z) and I want to apply a uniform
> > field across it in the z direction. The example in the autotest
> > directory is not particularly clear to me. At any rate, is the idea that
> > I model the electric field by inserting sheets of positive and negative
> > charges (so that I basically have a parallel plate capacitor with
> > graphene between the plates)?
> >
> > thanks,
> > -Ashwin.
> >
> >
> >
> >
> >     On Wed, Aug 4, 2010 at 6:00 AM,
> >     <dftb-plus-user-request at dftb-plus.info
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> >           1. Re: Applying an electric field with periodic      boundaries
> >              (Ben Hourahine)
> >
> >
> >
> ----------------------------------------------------------------------
> >
> >         Message: 1
> >         Date: Wed, 04 Aug 2010 10:05:44 +0100
> >         From: Ben Hourahine <benjamin.hourahine at strath.ac.uk
> >         <mailto:benjamin.hourahine at strath.ac.uk>>
> >         Subject: Re: [DFTB-Plus-User] Applying an electric field with
> >         periodic
> >                boundaries
> >         To: User list for DFTB+ related questions
> >                <dftb-plus-user at dftb-plus.info
> >         <mailto:dftb-plus-user at dftb-plus.info>>
> >         Message-ID: <4C592D68.7000904 at strath.ac.uk
> >         <mailto:4C592D68.7000904 at strath.ac.uk>>
> >         Content-Type: text/plain; charset=ISO-8859-1
> >
> >         Hello Ashwin,
> >
> >         what type of electric field do you need to apply? Currently the
> code
> >         can only include point charges when using periodic boundary
> >         conditions.
> >         The syntax is described in the  ElectricField section in the
> >         dftb+ v1.1
> >         manual, and there is an example in the autotest directory at:
> >         scc/H2O-extchrg-periodic
> >
> >         This is not equivalent to the recent methods to calculate
> properties
> >         with constant values of E, D or P based on the modern theory of
> >         polarization.
> >
> >         Regards
> >
> >         Ben
> >
> >         Ashwin Ramasubramaniam wrote:
> >         > Hello DFTB+ users,
> >         >
> >         > I see from the manual that an external field can only be
> >         applied for
> >         > non-periodic systems. Presumably a periodic system requires
> >         the use of
> >         > point charges. Is there an example available (or would any of
> >         the users
> >         > be kind enough to share one) for how to go about applying an
> >         external
> >         > field using point charges in the periodic case?
> >         >
> >         > thanks,
> >         > -Ashwin.
> >         >
> >
> >         --
> >             Dr. B. Hourahine, SUPA, Department of Physics,
> >           University of Strathclyde, John Anderson Building,
> >                  107 Rottenrow, Glasgow G4 0NG, UK.
> >            +44 141 548 2325, benjamin.hourahine at strath.ac.uk
> >         <mailto:benjamin.hourahine at strath.ac.uk>
> >           The University of Strathclyde is a charitable body,
> >         registered in Scotland, with registration number SC015263
> >
> >
> >
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> >         End of DFTB-Plus-User Digest, Vol 32, Issue 3
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