[Pw_forum] Methods of analyzing chemical bonds

[Axel Kohlmeyer]

On Wed, 25 Jun 2008, Clark Lee wrote:

clark,

a number of comments on your mail.

my observeration on open source software projects
are: if something is not documented, it usually
is not working well or well maintained. if that doesn't
scare you, you'd have to search the source code.
if you want something bad, you'll have to implement
it yourself or make a good case that that people will
do it for you. 'i want it', or 'i think it is useful'
is not very convincing to most... if they wouldn't want
it or thought it was useful they would not be working
on what they are working on right now. so you'd have
to come up with something that will make somebody drop
what he or she is doing and do something else instead.
just think of what would make you do that?

please keep in mind that the ratio of what you get from this 
package to what you paid for it is infinitely large. in some
cases people has offered a "bounty" to programmers to implement
certain features into their code of choice...

a couple more details, AIM can be done with outside packages,
all you have to do is to create an _all-electron_ density.
this is of course a problems for pseudopotential calculations
and you'd need to see if the PAW reconstruction can write this
out for you or you'd have to fudge it somehow.

you'll also have to keep in mind that all methods derived
for local basis sets first require a projection from the
plane wave basis on local orbitals, which can be a big
problem, as the projection is not complete due to the 
diffuseness of the plane wave basis and the lack thereof
of the corresponding local basis sets. this in turn can
reduce the accuracy of the methods you describe significantly
and make them less useful than density differences. they
don't have to, but they can.
... and again you are missing the core orbitals which may
(or may not) be important.

i hope this puts a few things into perspective...

cheers,
   axel.


-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
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If you make something idiot-proof, the universe creates a better idiot.