[Pw_forum] CuO, LDA+U, Pseudopots, etc.

[Agostino Migliore]

Hello

I refer to cations in solution (e.g., Fe2+/Fe3+). Indeed, I explored all
parameters and concluded that "the" minimum can be safely found. The only
problem is that for some configuration of the system and some particular
value of the mixing_beta parameter the calculation ends on a local
minimum. In these (indeed infrequent) cases, anyway the (same) minimum is
gotten along a wide range of the mixing_beta parameter, while a higher
minimum (e.g., the energy is 0.01 Ry more, which is significant for my
work) is reached at a particular mixing_beta value.
Let me express my agreement for the consideration about hybridization, on
which I reflected between this email and the previous one.

Agostino

>
> Hi Agostino
>
> what kind of system are you referring to? it must be one with several
> minima. if this is the case I think you get to a different one changing
> whatever parameter in the input just because of (slightly) different
> initial conditions or numerical noise that may bias the system towards a
> different state. I'm not sure what could be a good way to explore them
> all or to bias the system towards the "right" (lowest energy) one. Maybe
> using fractals..... (just kidding). Seriously, if one can distinguish
> the minima then one can write a constraint but what is a relevant degree
> of freedom to perturb in general?
>
> Thinking of CuO I have the suspect that in this system the hybridization
> between Cu and O is important (although the electron may still be quite
> localized). If this is the case then the lda+U on atomic orbitals may be
> not a good idea because it will force integer occupations on atomic
> orbitals
> while hybridization requires sharing of electrons between different
> atoms. Probably wannier functions (that Paul was going to try) are a
> better option.
>
> Matteo
>
>
>