The ABINIT Users Mailing List ( CLOSED )

[Natalie Holzwarth <natalie@wfu.edu>]

Dear abinit users,

      I am very glad to help with the atompaw program and to try to help
generate basis and projector functions for any particular project when I
have time.  (In the past I have some times promised to help and then could
not find the time.)  Nick Dellaripa is working with me for a few months
(before he goes to graduate school) to up date the web pages
http://www.wfu.edu/~natalie/papers/pwpaw/man.html and we will
be happy to test and include basis functions generated by other users.

Unfortunately, there is no full-proof recipe that works every time, and it
can be very time consuming to find and test good functions.  For what it
is worth, here are some guidelines that I use:

1.  Find the maximum rc for each atom for the particular set of materials
you will study so as not to have overlapping augmentation spheres.  (Some
overlap is OK, but not too much.)   Your rc values should be that value or
less.
2.  Decide which electrons should be valence and which should be core.
If you are studying an elemental material, the outer valence electrons
should be fine.   If you are studying a material which has positive ions,
it may be necessary to use the upper core states as well as valence states
in your basis set.  If you want to work with excited states , it would be
good to include some additional positive energy states for each l value as
well.
3.  Check the logderivative plots.  If there is a ghost state in the
middle of the range of interest, you will need to choose a different rc or
choose different basis functions.  (The worst example we found was P in
which case we had to use a 2s3s2p3p basis set in order to get rid of the
ghost resonance.)  I think that Ga and As may also have this problem.
4.  Find a simple example of the materials you are interested in and try to
test the converence and accuracy of the function you generated on that.
Ideally, I like to compare our results with an independent program such as
wien2k.

Marc Torrent has written a very nice manual about all of this which he
will put on the abinit web page if it is not there already.  I should
mention that we recently discovered that while most basis sets give nearly
identical results for pwpaw and abinit, some are slightly off in the
+-0.001 Ry range.  It would be nice to understand this descrepancy ...


Thanks for your interest in the atompaw program.  Your feedback is always
welcome.

                            Thanks, Natalie Holzwarth

PS.  Did you mean Cr?   A small rc would be needed for CrN perhaps.


On Fri, 13 Apr 2007, paul fons wrote:

> I would also second this request.  The documentation for atompaw has
> not kept pace with it development.  While some parameters are obvious
> (loggrid, scalarrelativistic), others are not.  In particular
> guidelines/advice on how to pick projector energies is lacking.
> There is also a dichotomy in the examples on the example potentials
> on Nancy Holzwarth's periodic table (http://www.wfu.edu/%7Enatalie/
> papers/pwpaw/periodictable/periodictable.html).  Here you can see
> example input files for atompaw as well as equation of state data for
> calculations in which the PAW potentials have been used.  The table
> has two classes of entries the older (labled unmodified in the table)
> entries all use the Vanderbilt scheme but do not enter any additional
> projectors/energies while the (newer, recent) entries labled modified
> entries do introduce such levels.   How to decide on these levels?
> It would be great to have a tutorial on this subject (it would answer
> a lot of people's question).  As of the moment it is a hard resource
> to use and it shouldn't be as it looks to be very useful.  In my
> limited tests, it seems to work fairly well, but I feel like I am
> working a little in the dark.  For example, in the examples folder
> for the latest version of atompaw there is a Cd example, however the
> core radius for this PS is set for 2.0 Angstroms.  Why such a small
> cutoff?  What was the logic behind it?  The answers to how to choose
> energy levels (I know it is a try and error process) as well as some
> educated comments about appropriate core radii would go a long way
> toward the generation and verification of PAW PS.
>
> Another idea would be to try and generate more elements of the period
> table as a group and then verifying them by calculating known
> materials EOS.  Doing this process as a group might lead to a useful
> table of elements that all can use.
>
> Just my thoughts,
>
>                                       Paul Fons
>
>
> Paul Fons
> Team Leader
> Nano-Optics Research Team
> paul-fons@aist.go.jp
>
> Center for Applied Near-Field Optics
> National Institute of Advanced Industrial Technology
> Tsukuba Central 4, Higashi 1-1-1
> Tsukuba, Ibaraki Japan 305-8562
>
> tel. +81-298-61-5635
> fax. +81-298-61-2939
>
> The following lines are in a Japanese font
> ???305-8562 ??????????????????????????????????????? 1-1-1
> ???????????????????????????
> ??????????????????????????????????????????
> ????????????????????????????????????????????????
> ????????????????????????
>
>
> On Apr 13, 2007, at 7:53 AM, snow9@llnl.gov wrote:
>
> >
> >
> > Guillaume, and others:
> >
> > I am interested in developing a Ga PAW set with atompaw, but have
> > only just begun using atompaw.  Would you mind sharing what you
> > have for Ga, that I can use as a guideline for my set?  Thanks a
> > million.
> >
> > -- Ryan
> >
> >
> > Quoting Guillaume Dumont <dumont.guillaume@gmail.com>:
> >
> >> Dear Paul,
> >>
> >> We actually had some trouble generating PAW datasets for Ga with
> >> the USPP
> >> package. As you suggest we figured out that the partial core
> >> corrections had
> >> a great impact on the physical properties one obtains with datasets
> >> generated with this package. On the other hand, AtomPAW has
> >> improved a lot
> >> since the first time I tried it. Personnaly, I find it easier to
> >> use than
> >> USPP. There is also a great manual written by M. Torrent that
> >> should be
> >> available on the web (is it?).
> >>
> >> At the last developper workshop, everyone agreed that a complete
> >> table of
> >> PAW should be generated by some of the developpers. So the fact
> >> that the
> >> list of elements is more complete with USPP should not be a
> >> problem anymore
> >> in the near future.
> >>
> >> Guillaume
> >>
> >> On 4/10/07, Paul Fons <paul-fons@aist.go.jp> wrote:
> >>>
> >>>  I have tried both methods of generating ultrasoft
> >>> pseudopotentials and
> >>> was under the impression that Nancy Holzwarth's system generated
> >>> more
> >>> reasonable pseudopotentials, but perhaps it was the non-linear core
> >>> corrections that were the problem.  Has anyone systematically
> >>> compared the
> >>> two methods?   The USPP pseudopotentials have the advantage that
> >>> there are a
> >>> lot of different input files for the elements already available I
> >>> have
> >>> noted.  On the other hand Nancy Holzwarth's pages have a periodic
> >>> table
> >>> linked with several tens of elements included as well.  On thing
> >>> that has
> >>> bothered me about this table is that none of the input files
> >>> create new
> >>> generalized basis functions (whereas the input file on the abinit
> >>> PAW page
> >>> for O does).    I have generated a PAW potential for Sb and it
> >>> seemed to
> >>> give reasonable results, but I am curious about others experiences.
> >>>
> >>>
> >>> Dr. Paul Fons
> >>>
> >>> Nano-Optics Reseach Team
> >>>
> >>> Team Leader
> >>>
> >>> National Institute for Advanced Industrial Science & Technology
> >>>
> >>> METI
> >>>
> >>> Center for Applied Near-Field Optics Research (CANFOR)
> >>>
> >>> AIST Central 4, Higashi 1-1-1
> >>>
> >>> Tsukuba, Ibaraki JAPAN 305-8568
> >>>
> >>>
> >>> tel. +81-298-61-5636
> >>>
> >>> fax. +81-298-61-2939
> >>>
> >>>
> >>> email: *paul-fons@aist.go.jp*
> >>>
> >>>
> >>> The following lines are in a Japanese font
> >>>
> >>> ??305-8562 ?????????????????????????? 1-1-1
> >>> ??????????????????
> >>> ????????????????????????????
> >>> ?????????????????????? ????????
> >>> ????????????????
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >> --
> >> Guillaume Dumont
> >> =========================
> >> guillaume.dumont.1@umontreal.ca
> >> dumont.guillaume@gmail.com
> >> (514) 341 5298
> >> (514) 343 6111 ext. 13279
> >
> >
> >
>
>
>
>
>

N. A. W. Holzwarth                      email: natalie@wfu.edu
Department of Physics                   www: http://www.wfu.edu/~natalie
Wake Forest University                  voice: 336-758-5510
Winston-Salem, NC 27109-7507            fax: 336-758-6142
U. S. A.