[Wien] berryphase

[Shahrbano Raheme]

Dear Prof. Rubel, and Sheikh, 
 >it's good to hear that everything worked with the fresh install. I am 
also interested to trace the origin of your previous problems, but I 
cannot reproduce the error. If you still have an access to the previous 
installation and can reproduce both correct and incorrect results, try 
to switch packages one-by-one, e.g. replace only BerryPI and see whether 
it makes a difference. Then do the same with W2W, WIEN2K. This way you 
can narrow down the reason.

In order to trace the problem, we tried to reproduce the error. To this 
end, we installed different versions of WIEN2WANNIER and BERRYPI. 
Eventually, we could find the source of the problem.  It originated from WIEN2WANNIER. As Sheikh said, I changed the w2w script. It worked and 
we could get good result. But, we still do not know what is the role of 
"*" in tmp="$(grep "lapw1 *-c" "$SEEDNAME.dayfile")". As far as I know –c flag is necessary when inversion symmetry is break 
down and complex calculations are needed to be performed by the WIEN2k 
code. I am not aware about "*-c" flag.  
>As far as I know, there is an internal relaxation in GaN wurtzite, which 
leads to slightly different Ga-N bond lengths (in c-direction and 
off-axis). Maybe the spontaneous polarization (Ps) is referred to a 
difference in polarization between two structures with relaxed and 
unrelaxed internal degrees of freedom? But I do not know for sure. How 
big is the value of Ps reported in the literature?

We are also not sure whether it is referred to the relaxed and unrelaxed 
structures. Thus, we tried to check it out. To do this, we selected the 
unrelaxed structure for lambda1and the relaxed one for lambda0. Our 
result is as follows:
3.16596720935 - 3.17586420101 = -0.00989699166   

But, this result is far from reported value in the literature, i.e., SP was 
reported to be -0.02 [PRB86, 081302(R) and PRB56, R10024].
  
> In any case, I would think what is the *measurable* quantity related to 
change of polarization in GaN and try to calculate that.

Does this mean that one has to try by changing the displacement reproduce 
the experimental value? In this case our result depends on the 
displacement. Can it be (in this case) an ab initio prediction?
 
Any comments or idea will be appreciated. 
> We suspected that BerryPI may not be compatible with earlier versions of 
numpy (before 1.6.2), but I don't think we actually tested it against 
numpy 1.4.1. The is the reason why init.sh is so picky. If you confirm that 
it works for you with numpy 1.4.1, we can loosen this requirement.

Yes, NUMPY 1.4.1 works as fine as NUMPY 1.6.2.

> Also regarding the Numpy version, We actually haven't tested BerryPI any 
Numpy older than v1.6.2. This is why the init.sh tries to ignore the 
older versions.

NUMPY 1.4.1 is not an old version of NUMPY. Indeed,  NUMPY 1.1.4 is the 
latest version of NUMPY that Fedora Core 14 automatically due to its 
repository install by yum command. NUMPY 1.6.2 is installed by yum in 
Fedora 17.

>>Another source of error could be from the older version of BerryPI which was 
using a different phase wrapping method. That was causing some issues to bring the phases between 0 to 2*pi or -pi to +pi range when some of the phases were close to 0 (may be positive or negative). The method  was 
completely ignoring those smaller values instead of unwarpping all the 
phases to same range. As a result, you would have phase values like 
1.999*pi 1.99996*pi 1.9994*pi -0.0001*pi instead of 1.999*pi 1.99996*pi 1.9994*pi 1.9999*pi. This would have messed up your average phase value and polarization.

We are still working on the above comment, but we are not sure whether we 
understand it completely. Clarification will help to do it. 

Thank for your cooperation.
SH. Rahimi
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20131201/9a7acb03/attachment-0001.htm>