[Wien] Deeper DFT question

[Florent Calvayrac]

On 23 July 2011 5:54 PM, Laurence Marks wrote:
> I am posting this email in the hope that someone can give me a hint
> about a "well-known" empirical DFT result, but one which I cannot
> rationalize/justify. Maybe someone can provide a counter example,
> which would prove that the result is not general.
>
> The empirical result can be phrased by looking at two cases:
> a) An scf run with the atomic positions at the equilibrium (i.e.
> lowest energy) positions
> b) An scf run with the atomic positions displaced from equilibrium,
> perhaps rather a lot.
>
> The empirical result is that a) converges faster, perhaps much faster
> than b) -- assuming of course equally good/bad starting points for the
> electron density (e.g. atomic densities).
>
> N.B., this result, if correct, implies something about the
> convexity/radius of convergence of the scf problem, and relates to the
> performance of MSR1a.
>
I have the same experience than you and even teach that it it is the
sign of something gone wrong (angstroms/bohr confusion in coordinates
or wrong spacegroup) but the point is on my opinion the initial guess.

I had the opportunity to work on hydrogen plasmas, in situations very far
from equilibrium, and there, with the correct initial guess, the 
calculations
would converge in a few steps. In highly compressed matter, for instance,
with a transition to some exotic conducting state, what would be a 
correct initial guess ?

-- 
Florent Calvayrac