[Pw_forum] End of SCF - convergence NOT achieved

[Tom Daff]

Hi Ben

It would probably be helpful to see your input file, as there are many
difficulties with iron and it could be any one of them!

What magnetism are you using? FCC iron is most stable in antiferromagnetic
double layer spin state (unless you are willing to look into spin-spiral),
and around the equilibrium volume there is a crossover in stability of the
high-spin and low-spin ferromagnetic states and I've found it difficult to
get convergence if you are off with the starting spin. 

I've found that mixing_beta = 0.1, with the default mixing scheme gives me
the most efficient convergence, and increasing the number of k-points can
sometimes help too.

Tom Daff

University of Cambridge



-----Original Message-----
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On
Behalf Of Ben Palmer
Sent: 28 June 2017 08:32
To: PWSCF Forum <pw_forum at pwscf.org>
Subject: [Pw_forum] End of SCF - convergence NOT achieved

Hi Everyone,

I'm trying to run a scf and vc-relax calculation for FCC Iron (nspin = 2).
I've managed to do this for a 4 atom example (although the final scf
calculation did fail: Error in routine ggen (138): smooth g-vectors missing
!).  When I scale up to 32 atoms, it fails to converge.

I've increased the number of steps to 250, used Plain, TF and local-TF
modes, changed the mixing mode, beta and ndim.  I've also tried increasing
nbnds and changing the starting magnetisation and celldm(1).

The structure looks fine and I'm using the output from the 4 atom vc-relax
calculation (scaled up 2x2x2).

I wanted to ask if anyone has any suggestions on what I could try in order
to get the calculation to converge?

Thank you.

Ben Palmer

student @ University of Birmingham



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