The ABINIT Users Mailing List ( CLOSED )

[Nicola Marzari <marzari@mit.edu>]

Dear Aaron,


very interesting. Could it be that those bands are free electron like 
bands that live mostly in
the vacuum region, and are lowered in energy when they are less confined 
(more spacing
between the confining graphene layers) ? Interlayer bands in graphite 
have been discussed since
~30 years ago (I believe by Posternak and Baldereschi), and 2-3 years 
ago in relation with
superconductivity in intercalated graphite (Csanyi et al - I believe 
Nature Materials).

Why they do not appear in Vasp might be related to the DIIS algorithm ? 
I believe DIIS
is not guaranteed to converge to the sequence of lowest eigenstates, 
just to eigenstates. Can
you use a different algorithm ?

            nicola


> On Tue, Aug 18, 2009 at 11:53 PM, Aaron Zhou<fishzhou@gmail.com> wrote:
>   
> > Dear all,
> >
> > I have a question when calculating graphene band structure. I leave a
> > 10 angstrom vacuum in Z-direction. But I saw many extra bands which
> > don't exist when doing the same thing in VASP. So I did a series of
> > calculation only changing the vacuum size, from 3A to 15A. I saw some
> > excited bands are pushed down from higher energy. Even 8 angstrom
> > vacuum and 10 angstrom vacuum will make big difference. That is quite
> > unexpected! I think the vacuum is already big enough to see the
> > convergence in band structure.
> >
> > Could someone tell me why those conduction bands are pushed down when
> > changing the vacuum size (acell(3) in input file)?
> >     


--
---------------------------------------------------------------------
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@mit.edu http://quasiamore.mit.edu