[molpro-user] No convergence in Boys Localization after 200 iterations

[Muammar El Khatib]

Dear Susi,

On Mon, Oct 21, 2013 at 03:06:51PM +0300, Susi Lehtola wrote:
> On Mon, 21 Oct 2013 13:12:52 +0200
> Muammar El Khatib <muammarelkhatib at gmail.com> wrote:
> > What would you suggest me to try?. I checked if there existed some
> > card to change the number of iterations, but I think that if in 200
> > it didn't do it so it's not a good idea to increase it. Then, there
> > is the option of localization thresholds but I'm not sure that it'll
> > make the localization to converge or what values are sensibles to do
> > it.
>
> In my recent experience, Boys localization can be pretty hard to do with
> first-order methods, because the minimum is often not well defined. 200
> iterations is not a very large number, you might have to increase it to
> 2000 iterations or so. But it still might not converge, especially if
> you use a diffuse basis set.

I increased the number of iterations from 200 to 1200, and the calculation
converged at the iteration number 234. JFTR, the file to change was
src/scf/locali.F.

>
> > PS. I tried using the Pipek-Mezey criterion and the calculation
> > converged, but I'm interested to know how to troubleshoot this
> > problem in Boys. This is because, even the Boys localization didn't
> > converge, the orbitals seem better localized.
>
> Pipek-Mezey usually converges much faster than the Boys criterion, so
> this is expected. Molpro also seems to have a second-order localization
> method implemented, which can help in tough cases. But this only seems
> to have been implemented for Pipek-Mezey, which usually doesn't have
> convergence problems in the occupied space. You may need it in the
> virtual space, though.
>
> PS. I didn't find any reference to the second-order method in the
> molpro manual. I guess it's the method by Leonard and Luken [Theor.
> Chim. Acta 62, 107 (1982)]; a citation should really be added..

Thank you very much for this reference, I read it completely and I get what you
mean about second-order localization methods.

Best regards,

--
Muammar El Khatib.
Linux user: 403107.
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http://muammar.me | http://proyectociencia.org
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