[Pw_forum] Convergence issue: spin-orbit + spin + electric field

[Giovanni Cantele]

Dear all,

I’m facing a hard convergence issue (never seen something like that before!) for a slab calculation, with spin-orbit coupling (SOC) included (full relativistic
calculation), and electric field (dipfield and tefield are both set to true) orthogonal to the slab plane.

Everything works fine (very easy to converge and quite reasonable results) until I want to check if, in the 
presence of electric field, spin polarisation shows up and set starting_magnetization to 0.5

In the latter case, self consistency is not reached, even after 200-300 iteration steps, independently on what
I do in the input file. In particular, this is what I tried (each setting separately or combined with some of the others, not
all the possible combinations have been tried):

i) increase ecutrho, to be sure that charge density with PAW pseudos is correctly represented

ii) decrease mixing_beta down to 0.3, 0.1, 0.05, 0.01

iii) set mixing_mode = ‘local-TF’

iv) increase degauss up to quite unreasonable values (0.2, 0.4, … Ry)

v) increase k-point grid, just to be sure that charge density and magnetisation sums are well converged


The convergence issue persists if tefield = dipfield = .true. AND eamp=0.00 (so, it is not a matter of electric
field magnitude, that is currently set to 0.01).

This would allow to conclude that there is an error in the input (e.g. eopreg or emaxpos), but as I said,
with the same settings I get reasonable results when SOC is turned on but the calculation is spin unpolarised
or SOC is turned off and the calculation is spin polarised.

It seems a no-hope calculation, but I’m wondering whether someone might suggest something else I’ve not tried
yet!

Thanks,

    Giovanni


-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele