The ABINIT Users Mailing List ( CLOSED )

[Aloysius Soon Sze Lok <a.soon@auckland.ac.nz>]

Dear Prof. Finocchi,
I'm also interested in the paper "Computer simulations of polar oxide 
surfaces". May I please have a copy of this paper?
Thank you in advance.


Best wishes,
Aloysius



On Friday May 28 2004 11:37 pm, Alexander Bagatur'yants wrote:
> Dear Prof. Finocchi,
> I am very interested in receiving the text of your article F. Finocchi, F.
> Bottin and C. Noguera, "Computer simulations of polar oxide surfaces"
> published in Computational Materials Science, edited by C.R.A. Catlow and
> E. Kotomin (NATO-ASI Series E, IOS Press, 2003), pages 196-217. Of course,
> an electronic form (pdf) would be much preferable.
> Many thanks in advance for your kind cooperation,
> Best regards
>
> Prof. Alexander Bagatur'yants
> Photochemistry Center, Russian Academy of Sciences
> ul. Novatorov 7a, Moscow, 119421 Russia
> Phone: (007-095)-936-2588
> Fax: (007-095)-936-1255
> E-mail: sasha@photonics.ru
>
> > -----Original Message-----
> > From: Fabio Finocchi [mailto:finocchi@gps.jussieu.fr]
> > Sent: Thursday, May 27, 2004 9:12 PM
> > To: forum@abinit.org
> > Subject: Re: [abinit-forum] Polar slabs and geometry optimization
> >
> > Dear Conor,
> > I read your email just now (!!!!). I hope you succeded in managing polar
> > slabs...
> > In any case, there are few hints below.
> > I have some experience in dealing with polar slabs. See, e.g. Bottin et
> > al, PRB 68 (2003) 035418, and references therein. I can also give
> > you, on request, the text of an article that recently appeared in the
> > proceedings of a NATO-ASI school [F.Finocchi, F. Bottin and C.
> > Noguera, "Computer simulations of polar oxide surfaces", in Computational
> > Materials Science, edited by C.R.A. Catlow and E. Kotomin
> > (NATO-ASI Series E, IOS Press, 2003), pages 196-217], where a detailed
> > analysis of the numerical problem is carried out.
> > First of all, the physics: if your slab does not fulfill the electron
> > counting rule, it is likely metallic (but not necessarily, since some
> > symmetry can be broken, which may open a small gap around EFermi).
> > Therefore, I would suggest you to use some smearing of the Fermi surface,
> > eventually using different values for tsmear (two are generally enough to
> > extract the T=0 total energy). Also, start a test calculation from
> > a slightly perturbed configuration with a low symmetry.
> > Second, the Broyden method is not very stable and can diverge whenever
> > the electronic structure is very sensitive to atomic relaxations. A
> > quasi-continuum damped dynamics (ionmov=7, with equal atomic masses
> > amu~4, vis~10, and dtion~50) is better suited when atomic forces are
> > less than, let's say, some mHa/bohr.
> > Third, we have a home-made version of the code in which a compensating
> > dipole in the vacuum region is used. However, due to the lack of
> > human time, nobody included it in a abinit version so far, to my
> > knowledge.
> > Nevertheless, some quantities, such as the total energy, are not
> > extremely sensitive to the use of a compensating dipole, provided that a
> > reasonable vacuum region is added in the supercell. This is because the
> > electrostatic potential is mostly biased in the slab outer regions,
> > where the electron density is small.
> > Others, like the work function, do actually depend on the use of a
> > dipole.
> >
> > Buona fortuna,
> > Fabio
> >
> > cdhogan@roma2.infn.it a écrit :
> > > Dear Abinites,
> > >
> > > Apologies in advance for the long post:  this will perhaps concern
> >
> > people with
> >
> > > experience in using slab geometries or with the internal workings of
> > > the code.
> > >
> > > I'm trying to optimize the geometry of a polar slab: GaAs(001) [back
> >
> > surface
> >
> > > passivated by pseudohydrogens, Z=1.25], and I'm quickly running out of
> > > options, as the calculation refuses to converge, at least with the
> >
> > Broyden
> >
> > > scheme.
> > > The slab is ~11 layers thick, and I've tried
> > > 7 and 11 layers of vacuum (the latter =15 Angs!). I'm using geometries
> > > converged with another code to start, and the same pseudopotentials
> > > (Hamann type from FHI code).
> > > For odd reasons, Im using Abinit 4.0.3, compiled with IFCv7.1, on a
> > > Dell
> >
> > Xeon.
> >
> > > Typical input parameters I've tried are:
> > > ionmov 3 or 2
> > > iscf 5 or 3
> > > diemac 12 or 8
> > > diemix 0.5 or 0.2
> > > iprcell 45 or undefined
> > > tolmxf 5e-4, toldff 5e-5 or lower
> > > k-points: Gamma pt, 1/2/4 points in IBZ (1/4 SBZ)
> > > The convergence of the SCF part is usually without problem, converging
> > > in 10-20 steps.
> > >
> > > However, the total energy and forces, while initially decreasing,
> > > jump to high values after a few steps
> > > and oscillate; the atomic positions overshoot, and the system never
> > > really seems to be relaxing smoothly - and even after this system has
> >
> > returned
> >
> > > to the original atomic coordinates the same instability occurs.
> > >
> > > I noticed that these jumps coincide with the one-dimensional
> >
> > electrostatic
> >
> > > potential showing a constant gradient in the vacuum (perp to surface),
> >
> > not to a
> >
> > > constant value. This I recognise as being associated with a macroscopic
> > > electric field in the cell appearing due to the periodic boundary
> > > conditions, which people have solved with dipole layers in the vacuum.
> > > In the absence of such a correction, I would expect to see such a
> >
> > constant
> >
> > > gradient at all times, even for fixed geometry, but this does not
> > > occur.
> > >
> > > So my questions are:
> > > 1) Can Abinit handle polar slabs?
> > > 2) Does Abinit have, or plan to, incorporate such a dipole layer in the
> >
> > vacuum?
> >
> > > (or do I have to tackle it myself...?!)
> > > 3) Has anyone managed to converge geometry for polar slabs, without
> > > just
> >
> > making the slab symmetric? (this would make my slabs too large)
> >
> > > 4) Has anyone any further suggestions or tricks for converging such
> > > structures,
> > > other than whats in the FAQ, etc.? Am I simply missing something?
> > > It was suggested to me that it might be a problem with the pseudo...
> > > 5) Where does the "sensitivity to the vacuum thickness" come from?
> > > Would a molecular dynamics calculation help?
> > >
> > > Any comments, criticisms or full solutions (!) are most welcome.
> > > All the best,
> > > Conor
> > >
> > > ---
> > > Dr. Conor Hogan
> > > Dipartimento di Fisica
> > > Universita' di Roma "Tor Vergata"
> > > Tel: +39 06 72594548
> > > Fax: +39 06 2023507
> > >
> > > What is it that makes a complete stranger dive into an icy river to
> > > save
> >
> > a
> >
> > > solid gold baby? Maybe we'll never know.  - Jack Handey
> > >
> > > To me, it's always a good idea to always carry two sacks of something
> >
> > when
> >
> > > you walk around. That way, if anybody says, "Hey, can you give me a
> > > hand?," you can say, "Sorry, got these sacks." - Jack Handey
> >
> > --
> >
> >       Fabio Finocchi
> >
> >        Groupe de Physique des Solides  (UMR CNRS 7588)
> >   Campus de Boucicaut, 140 rue de Lourmel, 75015 Paris (France)
> >   tel: (33) 1 44275116    fax: (33) 1 43542878    bureau: 2.1.5

-- 
Aloysius Soon SL
Postgraduate Student
Structural & Computational Chemistry
Chemistry Department
The University Of Auckland, New Zealand
Phone: +64 9 373 7599 ext 88291
Email: a.soon@auckland.ac.nz