[Smeagol-discuss] Problems in charge and convergence

[Wei Fan]

Dear  Stefano,

Thank you very much for your suggestions. In my calculations,  the
parameters for charge integration are

NEnergReal          857
NEnergImCircle       20
NEnergImLine         20
NPoles               10

I have tried to increase NEnergReal to 2000, but it helped a little. Then
when I increase MaxScfSteps to 800,  the charges finally converged after
really a lot of steps. Although it takes much, it works anyway.Is there a
possible way to accelerate the convergence for higher bias?

Thanks in advance!
Wei

On Sat, Mar 22, 2008 at 5:59 AM, Stefano Sanvito <sanvitos at tcd.ie> wrote:

> Hi Wei,
>
> > 1) In my calculations, the zero bias charges converged to 194.02 when it
> is
> > 194.00 in the first scf step. I am not sure if it's acceptable. However,
> the
> > weird thing is that the converged charge gets bigger when bias is
> larger,
> > 194.03 when bias=0.1V, 194.037 when bias=0.2V,  194.044 when bias=
> 0.3V......
> > Does it make sense or is there something wrong?  Btw, The system
> consists
> > of  two wire Al leads along 111 with a 1,4-benzene-dithiolate in the
> > center.  The system is recognized as a Chain in siesta.
>
> In general there is nothing particularly wrong with that. The
> electrostatics is
> different at different bias and it is not surprising that the
> self-consistent
> charge density in the scattering region changes with bias. Whether this is
> correct for the specific system you are looking at, it is difficult to
> say.
> Usually problems arise when the charge density systematically decreases
> with
> bias (by many electrons). This is not the case here, so this looks
> approximately OK.
>
> > 2) Generally, I can't get converged densities when bias is above 1 volt
> with
> > a 10-4 tolerance. The charge difference in those biases with zero bias
> is
> > more than 0.1.  Is there something responsible for this?
>
> There might be several reason for that. Did you try to change the number
> of
> energy points along the real axis? You might not have too many and the
> charge
> density is integrated on a too course grid. How many are you using?
>
> Regards,
>
> Stefano
> --
> Prof. Stefano Sanvito
> School of Physics and CRANN,
> Trinity College Dublin, IRELAND
> Tel: +353-1-8963065
> www.smeagol.tcd.ie
>
>


-- 
Wei Fan
Room 332, Main Building
Nano-Organic Photoelectronic Laboratory
Technical Institute of Physics and Chemistry
Beijing, China, 100101
Tel: +86-13811270970
+86-10-82680161
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