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[Anglade Pierre-Matthieu <anglade@gmail.com>]

Hi,

Atoms flying all around the cell is a symptom of unconverged
calculation. If your SCF cycles converge correctly (your "nstep 10"
looks quite scary here)  it can be the use of an ecut too low for the
pseudopotential...
Have you tried using a PAW pseudopotential ?

regards

PMA

On Wed, Apr 8, 2009 at 10:23 PM,  <cszakacs@mun.ca> wrote:
> Hello,
>
> I have used a lower cutoff, but now I am encountering another problem. Even
> though it didn't fully converged yet, I am detecting some strange things, it
> seems the cluster explodes....the Zn and O atoms are flying all around the
> box...it is a mess.
> (I have optimized the same cluster using other software (Gaussian) at HF 
> level
> of theory with no problem, but if I want to tackle significantly larger
> clusters it will be a problem, that is why I am testing the optimization  
> with
> Abinit.)
> The input file it is the same, as in my earlier email, I've changed the 
> ecut and
> I am using the TM pseudopotentials.
> Any suggestions?
> Or I would appreciate any directions to an article or some literature which
> deals with ZnO clusters using Abinit.
> I've looked around and I didn't find any yet.
>
> Thanks,
>
> Csaba
>
>
> Quoting matthieu verstraete <matthieu.jean.verstraete@gmail.com>:
>
>> your cutoff is huge - you should find softer pseudopotentials, and
>> converge the box size more systematically, starting with a small one
>> and looking at different quantites as a function of acell. You may
>> even have to go to bigger boxes to converge properly.
>>
>> Also consider using icoulomb for boundary conditions in the Poisson
>> solver (places constraints on the box shape and pseudopotentials,
>> though).
>>
>> Matthieu
>>
>> On Thu, Apr 2, 2009 at 2:27 PM,  <cszakacs@mun.ca> wrote:
>> > Dear users,
>> >
>> > I am testing some zero-dimensional calculations with Abinit. I am 
>> > following
>> the
>> > example given in Lesson 1 (with the hydrogen).
>> > I want to optimize a ZnO cluster containing 12 atoms in a supercell (I am
>> > considering it to be neutral). Here is my input:
>> >
>> > acell 30 30 30
>> > ecut 80
>> > #optimization
>> > natom 12
>> > ionmov 3             # Use the modified Broyden algorithm
>> > ntime 10            # Maximum number of Broyden "timesteps"
>> > tolmxf 5.0d-4        # Stopping criterion for the geometry optimization :
>> when
>> >                         # the residual forces are less than tolmxf, the
>> > Broyden
>> >                         # algorithm can stop
>> > xangst           1.69555300   -0.71202600   -1.53300200
>> >                 -0.23112400    1.82435000   -1.53300200
>> >                 -1.46439400   -1.11236700   -1.53302300
>> >                  0.23532700   -1.75354400   -0.85437000
>> >                  0.23971200   -1.71537200    1.06255400
>> >                 -1.63626200    0.67295000   -0.85436900
>> >                 -1.60538200    0.65003600    1.06257500
>> >                  1.40092400    1.08057300   -0.85436500
>> >                  1.36569300    1.06523600    1.06259300
>> >                  1.76646300   -0.70453700    1.71357600
>> >                 -1.49337800   -1.17754600    1.71354300
>> >                 -0.27303100    1.88202800    1.71359200
>> >
>> >
>> >
>> > toldff 5.0d-5        # Will stop the SCF cycle when, twice in a row,
>> >                         # the difference between two consecutive
>> evaluations
>> > of
>> >                         # forces differ by less than toldff (in
>> Hartree/Bohr)
>> > nband  108            #  band for energy calc
>> > #Definition of the atom types
>> > ntypat 2          # There is only one type of atom
>> > znucl 8 30           # The keyword "znucl" refers to the atomic number of
>> the
>> >                  # possible type(s) of atom. The pseudopotential(s)
>> >                  # mentioned in the "files" file must correspond
>> >                  # to the type(s) of atom. Here, the only type is
>> Hydrogen.
>> >
>> >
>> > #Definition of the atoms
>> > typat 1 1 1 2 1 2 1 2 1 2 2 2        # For the first dataset, both 
>> > numbers
>> will
>> > be read,
>> >                  # while for the second dataset, only one number will be
>> read
>> >
>> > #Definition of the k-point grid
>> > nkpt 1            # Only one k point is needed for isolated system,
>> >                  # taken by default to be 0.0 0.0 0.0
>> >
>> > #Definition of the SCF procedure
>> > iprcel 45
>> > nstep 10          # Maximal number of SCF cycles
>> > #toldfe is no more defined, as toldff is used above...
>> > diemac 2.0        # Although this is not mandatory, it is worth to
>> >                  # precondition the SCF cycle. The model dielectric
>> >                  # function used as the standard preconditioner
>> >                  # is described in the "dielng" input variable section.
>> >                  # Here, we follow the prescriptions for molecules
>> >                  # in a big box
>> >
>> > The main problem I am encountering is the huge memory needed and the 
>> > length
>> of
>> > the computation (about 8GB memory and the calculation is runnning now 
>> > for a
>> few
>> > days and it didn't finished yet.)
>> >
>> > Is this normal? Or I am using a too large ecut?
>> > I have done before some calculation on the bulk ZnO and using 80 as the
>> value
>> > for the ecut I've got good convergence, so I considered that this would 
>> > be
>> ok.
>> > Or are there other things that I've missed?
>> > Or the acell parameters are to high?
>> >
>> > Could you give me some advice about this?
>> >
>> > Thank you,
>> >
>> > Csaba Szakacs
>> >
>> >
>> >
>> >
>>
>>
>>
>> --
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Dr. Matthieu Verstraete
>>
>> European Theoretical Spectroscopy Facility (ETSF)
>> Dpto. Fisica de Materiales,
>> U. del Pais Vasco,
>> Centro Joxe Mari Korta, Av. de Tolosa, 72,   Phone: +34-943018393
>> E-20018 Donostia-San Sebastian, Spain        Fax  : +34-943018390
>>
>> Mail : matthieu.jean.verstraete@gmail.com
>> http://www-users.york.ac.uk/~mjv500
>>
>>
>
>
> --
> Csaba Szakacs
> PhD Candidate
> Memorial University
> Dept. of Chemistry
> St. John's, NL
> Tel.: 737-6118
>
>
>



-- 
Pierre-Matthieu Anglade