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

Ok, it's better (thanks to PMA), but still not entirely satisfactory: with nline 9, the tolwfr goes down, albeit more slowly, to 1.e-17 (so far). However the tolvrs is still stuck at 1.e-4 after 70 steps.

With all the symops I get

 ETOT 32  -11.444990018007     1.243E-14 9.972E-21 3.357E-20 0.000E+00 0.000E+00

beautiful... So why is it so dependent on the non-symmorphic operations? The number of kpoints is the same.

For the symmorphic operations in the normal cell, you no longer have inversion symmetry. Changing to a cell with inversion symmetry (origin in the middle of the C-C bond), many more of the operations are non-symmorphic; neglecting these you do not even have a null force on the atoms (only 8 symops left, 343 kpt instead of 127). However, it looks like all the other tolerances are converging:

 ETOT 21  -11.444989920147    -8.717E-12 1.188E-13 2.693E-05 8.456E-04 4.227E-04

So, it looks like the wfr and potential convergence depends on having inversion symmetry, whereas getting correct forces needs some of the other symops (probably the 3-axes - I am now trying with a cell preserving both inversion and 3-axes).

Matthieu

On Tue, Mar 3, 2009 at 8:44 AM, Anglade Pierre-Matthieu <anglade@gmail.com> wrote:

Hi Matthieu,

Could it be related to the default value of nline which is sometime a
bit too small for large systems ? Have you tried a larger value for
nline in the case with removed symmetry operations ? If so, is the
behavior similar ?

regards

PMA

On Tue, Mar 3, 2009 at 12:29 AM, Matteo Giantomassi
<Matteo.Giantomassi@uclouvain.be> wrote:
>  Hello abinists,
>>
>> I have come upon a strange behavior in abinit (not the first, of course)
>> and
>> was wondering if anyone had heard of it or an explanation (v5.6 on opteron
>> 64 bit RHEL, g95 compiled, sequential).
>>
>> In converging a ground state for graphene (what else), I need to use only
>> symmorphic symmetry operations. The strange behavior is that, without the
>> non-symmorphic symmetry operations, abinit does not converge the
>> wavefunctions below 1.e-13 or so (even after 200 steps), and the
>> eigenvalues
>> are not converged below mHa accuracy. With all the symops the convergence
>> down to tolwfr 1.e-20 is effortless. Why the difference? Numerical noise
>> is
>> one possibility, but plenty of symops are left in the calculation...
>>
>  Hi, Matthieu
>
>  I've never encountered such a kind of problem but
>  it might be related to a partial fulfillment of the symmetry properties
>  of the density and of the generated potentials.
>  Do you have the same number of k-points in the IBZ when non-symmorphic
>  operations are removed?
>
>  Just for curiosity: are you pruning non-symmorphic ops because you want to
>  generate a KSS file for GW calculations with abinit?
>  In this case please note that symmorphi=0 is not mandatory anymore
>  as the GW part is now able to handle non-symmorphic space groups.
>
>  Cheers,
>  Matteo
>
>
>
>

--
Pierre-Matthieu Anglade

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

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

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Mail : matthieu.jean.verstraete@gmail.com

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