[Pw_forum] vc-relax

[Axel Kohlmeyer]

On Sat, 24 Jan 2009, hania djani-ait aissa wrote:

HDA> 
HDA> Dear all,

HDA> i am doing calculation on orthorombic system containing 36 atoms 
HDA> (Bi2WO6). My computer is a workstation HP xw6400 quad-core Xeon, 
HDA> 2GB. Vc-relax on this system spent more than 01 mounth and still 

congratulations for your patience. i would have thought about 
alternate ways bring this to a result long ago.

HDA> not finish. the energy is converging but forces fluctuate. is there 
HDA> something wrong in my input in terms of umass or dt? or have i to 
HDA> capitulate to this very slow convergence?

one thing to consider is the fact, that your oxygen atoms
are over ten times lighter than your other atoms. that means
that the (much) heavier atoms can kick them around good, even
with little movement. for structural relaxation, mass doen't 
matter, so i would set all atoms to the same atomic mass.

HDA> here is the input file. Any suggestions will welcome. 

since you have constrained computational resources, have you
tried running a smaller version of this system first and finding
out the optimal parameters for the cutoffs and convergence thresholds?

also, it looks like you have imbalanced k-point sampling.

cheers,
    axel.

HDA> &control calculation = 'vc-relax' restart_mode = 'from_scratch' 
HDA>pseudo_dir = '/root/pwscf/pseudo/' outdir = '/root/tmp/' tstress = 

are you running this as root user???? 
if yes, be glad you are not a phd student of mine...


[...]

HDA> thanks a lot
HDA>  
HDA> Hania Djani-ait aissa
HDA> PHD student
HDA> Algeria
HDA>  
HDA>  
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-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
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