[Wien] follow up - *warning* ENE:

[Jorissen Kevin]

If you don't want to compile wien yourself, you could do
grep :RKM case.scf
to find out what your actual rkmax is (and see how much lower it is than what you put in case.in1(c)).  From that value on, you could do a few calculations with lower rkmax to see how bad convergence is.
 
As for your second point : For a given accuracy, the number of k-points needed (in the full brillouin zone) is roughly proportional to the inverse of the volume of the unit cell.
 
A last point :
* rkmax determines the size of the hamiltonian matrix which has to be diagonalized
* the number of k-points determines how many of these matrices have to be diagonalized
 
So increasing the k-mesh only increases the computation time, but not the memory requirements.  The maximal rkmax you are able to get, does not depend on your k-mesh.
 
 
 
Oh no, this is the last point :
for vacancy studies, optimization of the structure may be more important than a few k-points extra (alas, it will also be more time consuming ...)
 
 
 
Kevin Jorissen
 
EMAT - Electron Microscopy for Materials Science   (http://webhost.ua.ac.be/emat/)
Dept. of Physics
 
UA - Universiteit Antwerpen
Groenenborgerlaan 171
B-2020 Antwerpen
Belgium
 
tel  +32 3 2653249
fax + 32 3 2653257
e-mail kevin.jorissen at ua.ac.be
 

________________________________

Van: wien-admin at zeus.theochem.tuwien.ac.at namens fabella
Verzonden: do 28-10-2004 3:34
Aan: Wien2k FAQ FAQ
Onderwerp: [Wien] follow up - *warning* ENE:



Hello Stefaan,

You were right about the change in RKMAX, i guess my cell was too large
for the value of NMATMAX.  I'm running on pre-compiled Wien2k so i
don't think the situation is going to get any better.

However, the data does show physical signs of a "vacancy"
calculation...i don't feel i can rely on the total energy if there is a
"*warning*" next to ENE:.

So, I've found a smaller supercell for the vacancy: P, 2x2x2, 32 atom
cell (which reduces to 26) that may give results without warning
messages for ENE.

----------------

In the same token i want a pretty good k-mesh for the vacancy
calculation so i guess i have to sacrifice size of the supercell to do
this....otherwise RKMAX becomes large for NMATMAX.  Is this correct?

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