[CPMD-list] BO-MD starting problem after successful WFO

[Axel Kohlmeyer]

On Wed, 6 Jun 2007, Vladimir Stegailov wrote:

VS> Dear colleagues,

dear vladimir,

VS> I am trying to do BO-MD of 32 atom system (non-perfect fcc aluminum
VS> crystal in 3D pbc). First I make a wave function optimization. Then
VS> I use the resulting restart file to begin MD. The WFO goes fine.
VS> However at the very beginning of the BO-MD stage the diagonalization
VS> fails. Program stops after a lot of "FRIESNER_C| EIGENVECTOR ...  
VS> IS VERY BAD!" messages.

it is not fully clear to me from your description, whether 
the problem happens right during initialization or after 
the first MD step.

however, there are a number of things with your input 
that may have some impact.

using compressed write will cut off some accuracy from your
wavefunction (it is a lossy compression!), so you are not
starting from the exactly same wavefunction.

using point group symmetry during MD is usually not a good idea.
the MD may break the detected symmetry and then all of your 
arrays are too small. i remember we had a problem because of
that a long time ago in geometry optimization, not sure whether
this is the same here.

VS> It seems strange to me. I expected that starting from a previously
VS> optimized w.f. there should be no diagonalization problems at least

the compression modifies the wavefunction...

VS> during several MD steps.  Please could you give any advice.

this can depend a _lot_ on how your system moves, how large
the velocities are and what happens during the steps. also
the fiddling with the lanczos parameters is almost always required
to get a stable MD with diagonalization.

it might also help to start from a random wavefunction instead
of an atomic guess. sometimes the guess leads the optimization
to a wrong state and some additional randomization then leads
to conversion problems.

finally, please try looking at the occupations and eigenvalues.
with 90 states you should be fine, but the error you see sometimes
also indicates, that for one of the k-points you don't have enough 
empty states.

cheers,
  axel.

VS> 
VS> My WFO and BO-MD scripts are below.
VS> 
VS> Thank you.
VS> 
VS> Vladimir
VS> 

-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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