[Pw_forum] speeding up vc-relax

[Nicola Marzari]

Well, since a system can be floppy for non van der waals reasons,
what is the best strategy to combat floppyness ?

Floppyness is akin to say that the ionic potential energy surface
has a very wide spread in eigenvalues - and the strategy that would
improve BFGS or ionic conjugate gradients minimization is
preconditioning.

There was a talk by Dominic King-Smith at ES2001, in Princeton,
on optimal choices of internal coordinates. I think he published
the work (around ~2001), or it might be on the Accelrys website.

			nicola


Paolo Giannozzi wrote:
> On Tuesday 17 January 2006 17:51, Nichols A. Romero wrote:
> 
>> I was doing vc-relax on a vdW bonded system
> 
> you shouldn't. Van der Waals bonded systems are not well
> described by DFT.
> 
> Paolo
>