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

[Nicola Marzari]

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



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