The ABINIT Users Mailing List ( CLOSED )

[Natalie Holzwarth <natalie@wfu.edu>]

Dear Paul,
     Some comments are listed below:

On Mon, 16 Apr 2007, Paul Fons wrote:

   I was attempting to go through the examples on the Lake
> Forest page (http://www.wfu.edu/%7Enatalie/papers/pwpaw/periodictable/
> periodictable.html).  On the Lake Forest page, the downloadable
> potentials seem to be of two flavours as reinforced by the somewhat
> cryptic label "Modified Elements" and "Unmodified Elements".  I
> didn't find a reference anywhere as to what these terms meant (pardon
> me if it was just my oversight).     We are trying to update the webpage
which was created in 2005 by a summer student, using the more recent
version of the programs.   The "modified elements" are the ones we have
worked on so far.      Of course, even if we have worked on an element, it
still needs to be tested by the user....

>
> I was curious to follow up on the mail by Natalie Holzwarth. First,
> the general guidelines in her email appear to be useful and provided
> some new information to me that I hadn't considered (e.g. the
> inclusion of positive energy states).  I wanted to take this
> opportunity to ask a couple of (what I hope aren't too) simple
> questions.
>
> 1. On the Lake Forest periodic table of PAW potentials, most of the
> potentials (the "unmodified" ones?) seem to use PS of the Trouiller-
> Martin norm conserving form using the Blochl scheme.  This would
> appear to have the advantage that there are fewer parameters to tweak
> (I am assume this is also its disadvantage!).  The new entries seem
> to use T-M PS, but with the Vanderbilt scheme.
>
> I was hoping that Natalie (or another person from her research group)
> would be so kind as to comment on the advantages/disadvantages of the
> two techniques.

In my own experience, the Bloechl scheme gives projector and basis
functions that "look" better when you plot them in real space, but often
the Vanderbilt scheme generated functions seem to converge faster in
Fourier space (smaller ecut or gcut).  I have no idea why this is.
Usually I just use one value of rc for everything, but Marc Torrent has
shown that you can get much better agreement of the logarithmic
derivatives if you adjust the matching radii for each wave function...

>
> 2.  On the Lake Forest page, there is the comment  "In addition to
> the manual prepared by Marc Torrent, notes on the method are
> available. (" The link pointing to the manual is dead while the page
> I can find on the abinit site would seem to be (http://www.abinit.org/
> PAW/AtomPAW2Abinit-Manual-html/HolzwarthPAW.htm) which appears to be
> a one page summary of how to compile the program and a couple of
> input files are included with a one line of explanation of what the
> input lines mean in a particular file, but there is not comment that
> I could find as to the logic of how to choose parameters or even what
> the naming scheme is for the different output files are. These two
> examples also both use the VNCT keyword (Blochl scheme Trouiller
> Martin PS).
>
>    Thanks for some advice in advance!
>

For constructing the local pseudopotential, the default (no extra key
word but specify l e) is to use the traditional Troulliers-Martins scheme
at angular momentum l and energy e.   I recommend that you choose l to be
one larger l-value than that of your basis and projector functions and the
energy can be 0.   Mark Torrent has introduced some additional key words
to fine tune the local potential.    For the projectors and basis
functions the key word BLOECHL is the same as the old VNCT and VANDERBILT
is the same as the old VNCTV.   Mark Torrent has also introduced some new
options here in such as way to be backward compatible.    In trying to
explain all this, it is clear that we should try to make this easier for
the users...    some day when we find some time....   In the mean time,
thanks for your patience and we always appreciate your feedback.

                                              Natalie
>
>

>
>
> 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
>

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.