[Q-e-developers] Problems converging anions in vacuum

[Stefano de Gironcoli]

I think the problem is that the threshold of eigenvalue is very tight 
because it was almost converged and then the wavefunction becomes very 
different and cannot be converged in a finite number of iterations.
maybe what one can do is to restart one of these calculations removing 
the recover file but starting from startingwfc ='file' to let the new 
scf develop from the new set of wavefunctions with some loose initial 
threshold and without memory of the "other" solution ... I dont know,  
just an idea.

stefano

On 05/12/2012 10:52 PM, Nicola Marzari wrote:
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>
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> Grazie Stefano,
>
>
> you are right indeed re the lower energy!
>
> We had tried larger number of bands and smearing (to no avail) but
> we'll look at this more in detail. We'll try it both the oxygen that
> works, and the one that doesn't work, to see if there is any difference
> in the empty states evolution.
>
> One question - what does it mean having a non converged eigenvalue in
> c_bands? Is it because all of a sudden the highest eigenvector wants to
> be really different, and either CG or Davidson do not manage to iterate
> the new eigenvector to convergence?
>
> Sorry to all for the bandwidth...
>
>                 nicola
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>
>
> On 12/05/2012 22:44, Stefano de Gironcoli wrote:
>> I think that for some reason, real or spurious, ghost or negative
>> affinity, there is a delocalized state close to the localized state that
>> almost converges and then suddenly the new state gets occupied and self
>> consistency goes bananas.
>> Notice however that the total energy of the first problematic iteration
>> is LOWER than the one the system was converging to. so what happens is
>> that the system suddenly finds a "better" solution and runs for it.
>>
>> I would (sorry if you already did it)
>> - start from atomic+random wfcs
>> - compute more that the strict minimum nbnd
>> - apply martyna-tuckerman or counter charge correction to have the zero
>> of the  potential properly set
>> - monitor eigenvalues at each iteration (iprint=1)
>> - study what happens as the cell size is increased.
>>
>> stefano
>>
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL