[QE-users] Calculating U parameter for Ni in LiNiO2 using hp.x

[Mohammad Moaddeli]

Dear Lorenzo,

Thank you so much.

Best

On Wed, Sep 16, 2020 at 1:19 PM Lorenzo Paulatto <paulatz at gmail.com> wrote:

> >> By changing the threshold values you mentioned, nscf calculation
> finished (no "cholesky" error)...
> This is a common problem and maybe would require an upstream fixing:
>
> when doing an SCF calculation, the diagonalisation threshold is set to a
> relatively loose value at the beginning, then tightened.
>
>       IF ( iter == 2 ) ethr = 1.D-2
>       ethr = MIN( ethr, 0.1D0*dr2 / MAX( 1.D0, nelec ) )
>       ! ... do not allow convergence threshold to become too small:
>       ! ... iterative diagonalization may become unstable
>       ethr = MAX( ethr, 1.D-13 )
> (from electrons.f90)
>
> On the other hand, in an NSCF calculation, the threshold for
> diagonalisation is proportional to the input convergence threshold.
>
> IF ( ethr == 0.D0 ) ethr = 0.1D0 * MIN( 1.D-2, tr2 / nelec )
> (from setup.f90)
>
> The latter can turn out to be much tighter than the former, and even
> impossibly tight sometimes which makes the algorithm fail. Maybe adding
> a minimu of 1.d-13 also for NSCF would fix this kind of problems, but
> I'm not 100% sure this is exactly how it is done, as there are several
> places where ethr is set.
>
> cheers
>
>
>
> --
> Lorenzo Paulatto - Paris
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