Dear Cherry:
The potential in the .VT (or equivalent)
file is in Rydbergs.
In the Macroave code, they are automatically translated
to eV.
Javier
-----Mensaje original-----
De: Cherry Y. Yates [mailto:[EMAIL PROTECTED]
Enviado el: vie 08/08/2008 2:17
Para: Junquera Quintana, Francisco Javier
Asunto: Re: [SIESTA-L] Work function of Si
By the way, I wonder the unit in .VT files (total potential) is Hartree, or
Rydberg?
Thanks!
Cherry
--- On Tue, 7/29/08, Javier Junquera <[EMAIL PROTECTED]> wrote:
> From: Javier Junquera <[EMAIL PROTECTED]>
> Subject: Re: [SIESTA-L] Work function of Si
> To: SIESTA-L@listserv.uam.es
> Date: Tuesday, July 29, 2008, 6:05 AM
> Dear Zubaer:
>
> Here you are a step by step recipe to compute the work
> functions with Siesta (is the same as for the band offset,
> or Schottky barriers).
>
> Some of the steps will be automatized in the near
> future,
> but I will assume for the time being that you are using
> version 2.0.1.
>
> 1. Edit the file dhscf.F, and add the following lines
> (here, we will write the value of the neutral atom
> potential,
> see page 2753 of the technical paper of Siesta,
> at the points of the 3D grid.
> The new output file is called Interface.VNA,
> but you can chose the name you want).
>
> C Find neutral-atom potential
> call NeutralAtomOnMesh( na, isa, ntpl, Vna, indxua,
> dvol,
> . volume, DRho, Fal, stressl,
> . .false., .false. )
>
> C START OF NEW LINES
> C
> ----------------------------------------------------------------------
> C Print the Neutral Atom Potential at the points of the
> grid
> C
> ----------------------------------------------------------------------
>
> call reord( Vna, Vna, nml, nsm, +1)
> call write_rho( 'Interface.VNA', cell, ntm,
> nsm, ntpl, 1, Vna)
> call reord( Vna, Vna, nml, nsm, -1)
> C END OF NEW LINES
>
> 2. Recompile the code.
> I suggest to include the flag "-DGRID_DP" after
> DEFS
> (it means that all the variables in the grid will be
> stored with
> double precision).
>
> DEFS=-DGRID_DP
>
> 3. You must perform a simulation for the surface (or
> interface)
> you are interested in.
>
> Be sure that the thicknesses (number of layers
> of the different materials) are large enough,
> and that all the atoms are properly relaxed.
>
> For a more detailed recipe, look at Section V of the
> review
> J. Junquera et al., J. Phys.: Condens. Matter 19, 213203
> (2008).
>
> Also, remember to switch on the flag:
> SaveElectrostaticPotential .true. # Write the total
> elect. pot. at
> the mesh
>
> 4. After a successful run of the code, you will have a
> file called
> SystemLabel.VH, and another called Interface.VNA (or
> whatever name
> you have chosen before).
>
> 5. Perform the macroscopic average of these two quantities,
> using
> the code MACROAVE, included in the Util directory.
> For more instructions about how to run and compile the
> code,
> read the User Guide in the Src/Util/Macroave/Docs
> directory.
> (You can also have a look at talk number 7 in
> http://personales.unican.es/junqueraj/talks.html).
>
> Save the different averaged potentials (.MAV files) in
> files with
> different names
> (for instance SystemLabel.VH.MAV, and SystemLabel.VNA.MAV).
>
> 6. Take the difference between the averaged
> electrostatic potential and the averaged neutral atom
> potential.
> This difference is the profile of the deformation potential
> (\delta V^H)
> across the interface.
>
> Plot this last profile, and identify the plateau values at
> the center
> of each material (for the case of an interface), or between
> the center
> of the vacuum region and the center of the slab (in the
> case of a
> surface slab
> simulation).
>
> The difference between the plateau values at the center
> of the materials is the Delta V term in Section V of the
> paper
> Phys. Rev. B 67, 155327 (2003).
>
> 7. Perform a bulk calculation for each material under the
> same
> strain conditions as in the interface or surface.
> Localize both the top of the valence (TVB) band and the
> bottom of the
> conduction band (BCB).
>
> 8. The difference between the TVB and BCB of the two
> materials
> is the term referred to as the band structure term
> in Section V of the previous paper.
>
> 9. Add the band structure term to the Delta V term.
> This is the final bandoffset or work function you are
> searching.
>
> Hope this helps,
>
> Javier
>
> > Hi Eduardo,
> >
> > Thanks for your reply.
> >
> > I read the papers referred in the links. But I could
> not understand
> > which step I am missing in my calculation. For a
> surface surface
> > calculation there should not be any potential shift.
> Average
> > electrostatic potential in the bulk is not coming into
> the picture of
> > calculating WF, I guess. Only thing that is needed to
> be considered is
> > the energy difference between vacuum level and Fermi
> level.
> >
> > I made sure that I was choosing correct options
> (surface, potential,
> > filter function length etc.) in macroave.in
> <http://macroave.in> file.
> > Plotting the *.PAV gives me the vacuum level. As I
> said I checked the
> > convergence of the WF (E_c - E_f) as function of slab
> and vacuum
> > thicknesses. So, the only place that I can make
> mistakes is probably
> > E_f, which lies in between Ec_min and Ev_max for
> semiconductors. I
> > dont know if shifting of E_f is necessary or if
> that's what I need to do.
> >
> > I appreciate any suggestions.
> >
> > Thanks,
> > Zubaer
> >
> > On Wed, Jul 23, 2008 at 7:45 AM, Eduardo Anglada
> > <[EMAIL PROTECTED]
> <mailto:[EMAIL PROTECTED]>> wrote:
> >
> > Hi,
> > Please take a look at this previous posting by
> Javier Junquera. He
> > has written
> > a nice review about the subject
> >
> >
> http://www.mail-archive.com/siesta-l@listserv.uam.es/msg00627.html
> >
> > Best regards,
> > Eduardo
> >
> >
> >
> > On 18/07/2008, at 20:34, zubaer wrote:
> >
> > Hi,
> >
> > I wanted to calculate the workfunction of a Si
> (001) surface
> > using SaveTotalPotential and
> SaveElectrostaticPotential and
> > then macroave.x utility.
> >
> > I checked the convergence in terms of slab
> layer and vacuum
> > thicknesses. Finding the vacuum level and
> subtracting the
> > fermi energy obtained from scf file, I got the
> value 5.51eV,
> > which is way higher compared to the
> experimental value of 4.85eV.
> >
> > Could you suggest what things I need to check
> to make a better
> > estimate.
> >
> > I appreciate any helps.
> >
> > Thanks,
> > Zubaer
> >
> >
> >
>
>
> --
> -------------------------------------------------------------------------
> Javier Junquera
>
> Ciencias de la Tierra y Fisica de la Materia Condensada
> (CITIMAC)
> Avenida de Los Castros s/n
> Facultad de Ciencias
> Universidad de Cantabria
> E-39005 Santander, Cantabria
> Spain
>
> web-page: http://personales.unican.es/junqueraj
> e-mail: [EMAIL PROTECTED]
> Tel: (+34) 942 20 15 16
> Fax: (+34) 942 20 14 02
