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[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

There is no optimum, simply it has to be large enough to accomodate the variations of your cell during the relaxation: if the cell gets larger, the reciprocal lattice vectors get smaller, and more plane waves fit into a sphere with radius sqrt(ecut). If npw increases too much, the arrays in memory are not big enough anymore and abinit has to stop.

You should look critically at how far you are from equilibrium, and the values of stress you got during the relaxation. If they are too large, either your structure is wrong or something else is unconverged, or your pseudopotential is bad (have you tested it?).

If you are sure the rest is ok, just re-start from the last, most relaxed, structure you have, and continue relaxing. Arrays will be redimensioned to fit the new initial cell.

Sometimes, if you are not close enough to a minimum energy structure, and the PES is not convex, the relaxation runs away and explodes the cell. Also, if it gets stuck in a local minimum and can't find an equilibrium structure, the BFGS algorithm eventually tries very large displacements away (in frustration).

Matthieu

On Wed, Mar 4, 2009 at 11:43 AM, Souraya Goumri-Said <Souraya.Goumri-Said@fundp.ac.be> wrote:

Dear Abinit users,

What is the optimal value of dilatmx ? sometime some calculation are stoped ans ask for enhancing the value of dilatmx = [1.5, 5] !

Can we change an other parameter in order to avoid this error?


Best regards,

Cordialement,
Sincerely yours,

====================================
Dr. Souraya Goumri-Said
Centre de recherche en Physique de la Matière et du Rayonnement (PMR)
Laboratoire de Physique du Solide
Facultés Universitaires Notre-Dame de la Paix
Rue de Bruxelles 61 - B - 5000 Namur
Tel : +32(0)81 72 47 01
Fax : +32(0)81 72 47 10
http://sourayagoumri-said.weebly.com/
email : Souraya.Goumri-Said@fundp.ac.be

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dr. Matthieu Verstraete

European Theoretical Spectroscopy Facility (ETSF) 
Dpto. Fisica de Materiales, 
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