[Pw_forum] Charge Density

[Paolo Giannozzi]

On May 11, 2008, at 5:12 , Paul M. Grant wrote:

> I’ve been assuming the units of charge density as stored in *.save  
> and used in plotrho and accessed by xcrysden are scaled as (number  
> of electrons/angstroms^3)
>

number of electrons/(a.u.)^3 is a better assumption (no warranty).  
PWscf uses atomic
(Rydberg) units everywhere, unless explicitly specified. In order to  
preserve genetic
diversity, guess what? CP uses Hartree atomic units.

> Also, some time ago (about three months!), I switched from  
> espresso-3.2.3 to o-sesame
>

you mean: the development version in the cvs repository, that for
historical reasons has 'o-sesame' as root directory?

> and noticed that the charge density files in *.save are in a *.dat  
> binary format rather than *.xml. What’s going to be the future  
> standard?
>

it was done to fix some inconsistencies in the naming convention:
   http://www.democritos.it:8888/O-sesame/chngview?cn=5687
See also the following for recent changes of the file format:
   http://www.democritos.it:8888/O-sesame/chngview?cn=5744
   http://www.democritos.it:8888/O-sesame/chngview?cn=5795
It is unfortunate that the file format had to be changed (once again)
at this stage, but these should hopefully be the last major changes
that can affect other people's software reading those files, if any
exists (Q-E will keep reading old files).

> Finally, and I think I asked about this before, is there a  
> developers guide to the bowels of pw.x?  The makefile links an  
> enormous number of object files and I suppose one could figure this  
> all out.
>

the closest thing to a developer's guide is, well, the "developer  
manual"
linked in the main page of the wiki:
   http://www.quantum-espresso.org/wiki/index.php/Developer_Manual
It used to be available as a latex file in previous versions. I wrote  
it as
a template some time ago and from time to time I add to it some piece
of information that I deem suitable. One can find there a few important
things like the specifications of the file format, but what is  
missing vastly
exceeds what is present.

Documentation of what a single *.f90 does is not supposed to be
written in the guide, though, but in each file. Sometimes there is
something useful (although in an unstructured way), sometimes
there is nothing useful, depending on the mood of the developer.

There are no flow charts of anything. If anybody knows any simple
automated way (e.g. by transforming code into linkable html) to
locate calls, variables in modules, etc, it would be very useful.

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222