[Pw_forum] MgFeO LDA+U convergence problem
sasha
ackollias at gmail.com
Tue May 15 16:30:21 CEST 2007
Greetings Matteo,
Thanks for the advice, your suggestion in fact works very well. It
turns out that I should have more closely examined my input. I have
another quick question regarding the starting_ns_eigenvalue, in the
previous example (below) from the eigenvalues at the first iteration of
the "standard" lda+u calculation it is clear how to set the
ns_eigenvalues however what does one do if the starting eigenvalues are
as follows:
atom 1 spin 1 0.9985560 0.9998587 1.0007556 1.0013322 1.0057882
atom 1 spin 2 0.0484071 0.0493657 0.0578860 0.1216687 0.1308162
atom 2 spin 1 0.0535213 0.0592929 0.1256650 0.1321563 0.1439048
atom 2 spin 2 0.9979128 0.9993943 1.0004671 1.0010265 1.0058542
atom 3 spin 1 0.9947113 0.9953027 0.9992115 0.9997585 1.0044052
atom 3 spin 2 0.0693133 0.1280564 0.1459512 0.1547219 0.4858838
atom 4 spin 1 0.0637767 0.0681158 0.1421888 0.1436934 0.2272403
atom 4 spin 2 0.9965028 0.9979222 0.9991654 1.0005289 1.0054916
where only some of the eigenvalues for certain atoms and spins are
degenerate? Once again thank you in advance for any advice or
suggestions.
regards,
Sasha
On Mon, 2007-05-14 at 09:48 -0500, Matteo Cococcioni wrote:
> Dear Sasha
>
> looking at your input (in particular at the spin arrangement you fixed)
> I think the starting_ns should be something like:
>
> starting_ns_eigenvalue(3,2,1) = 1.d0
> starting_ns_eigenvalue(3,1,2) = 1.d0
> starting_ns_eigenvalue(3,2,3) = 1.d0
> starting_ns_eigenvalue(3,1,4) = 1.d0
>
> Maybe it would also make sense to have different starting magnetization
> on the Fe iron so that the breaking of their equivalence is more
> complete from the beginning:
>
> starting_magnetization(1)= 0.8,
> starting_magnetization(2)=-0.7,
> starting_magnetization(3)= 0.4,
> starting_magnetization(4)=-0.5,
>
>
> Another possibility is to (slightly) move the Fe iron from their
> positions. Residual symmetries would be lost and maybe the code is able to
> find the ground state and the occupation pattern you are trying to impose.
>
> Hope this helps,
>
> Matteo
>
>
>
>
>
> sasha wrote:
> > Greetings,
> > I am having difficulties converging an insulating AFM solution
> > for (Mg,Fe)O using LDA+U. The starting ns_eigenvalues are manually set,
> > see input file below, based on the eigenvalues from a standard LDA+U
> > calculation ( similar to the calculations found in example25 that comes
> > with pwscf), i.e. from a "standard" lda+u calculation the eigenvalues at
> > the first iteration for each Fe atom and spin are:
> >
> > atom 1 spin 1 0.9963065 0.9965670 0.9992693 1.0013531 1.0014491
> > atom 1 spin 2 0.0596477 0.0599690 0.1193848 0.1515851 0.1529077
> >
> > atom 2 spin 1 0.0596467 0.0599706 0.1193259 0.1496419 0.1509636
> > atom 2 spin 2 0.9963062 0.9965635 0.9992686 1.0013520 1.0014480
> >
> > atom 3 spin 1 0.9963065 0.9965668 0.9992693 1.0013532 1.0014491
> > atom 3 spin 2 0.0596468 0.0599704 0.1193283 0.1497012 0.1511213
> >
> > atom 4 spin 1 0.0596478 0.0599688 0.1193870 0.1516467 0.1530634
> > atom 4 spin 2 0.9963069 0.9965703 0.9992700 1.0013546 1.0014500
> >
> > Initially the calculation proceeds normally however after a number of
> > iterations the SCF accuracy no longer improves and in fact begins to
> > increase, see output snippet below:
> >
> > Energy SCF accuracy
> > -484.47448064 10.17038034
> > -485.86491483 0.86693260
> > ... ....
> > -486.21197435 0.00002051
> > -486.21199031 0.00002066
> > -486.21190314 0.00002043
> > -486.21186241 0.00002073
> > -486.21188439 0.00002073
> > -486.21185625 0.00002089
> >
> > I have tried various combinations of degauss values and increasing the
> > number of bands with no success. Which values or input setting could be
> > used to achieve convergence in this system For the clarity's sake my
> > input file is included below. Any help or suggestions are greatly
> > appreciated.
> >
> > regards,
> > Sasha
> >
> > Input file:
> >
> > &system
> > ibrav= 0, celldm(1)=8.19, nat= 16, ntyp= 6,
> > ecutwfc = 30.0, ecutrho = 240.0, nbnd=53
> > starting_magnetization(1)= 0.5,
> > starting_magnetization(2)=-0.5,
> > starting_magnetization(3)= 0.5,
> > starting_magnetization(4)=-0.5,
> > starting_magnetization(5)= 0.0,
> > starting_magnetization(6)= 0.0,
> > occupations='smearing', smearing='gauss', degauss=0.01,
> > nspin=2,
> > lda_plus_u=.true. Hubbard_U(1)=5.0, Hubbard_U(2)=5.0,
> > Hubbard_U(3)=5.0, Hubbard_U(4)=5.0,
> > starting_ns_eigenvalue(3,2,1) = 1.d0
> > starting_ns_eigenvalue(3,1,2) = 1.d0
> > starting_ns_eigenvalue(3,1,3) = 1.d0
> > starting_ns_eigenvalue(3,2,4) = 1.d0
> > report=1
> > /
> > &electrons
> > mixing_mode = 'plain'
> > mixing_beta = 0.20
> > mixing_ndim = 5
> > mixing_fixed_ns = 0
> > conv_thr = 1.0d-6
> > electron_maxstep = 100
> >
> > /
> > CELL_PARAMETERS
> > 1.00 1.00 0.00
> > 1.00 0.00 1.00
> > 0.00 1.00 1.00
> > ATOMIC_SPECIES
> > Fe1 1. Fe.pz-nd-rrkjus.UPF
> > Fe2 1. Fe.pz-nd-rrkjus.UPF
> > Fe3 1. Fe.pz-nd-rrkjus.UPF
> > Fe4 1. Fe.pz-nd-rrkjus.UPF
> > Mg1 1. Mg.pz-n-vbc.UPF
> > O1 1. O.LDA.US.RRKJ3.UPF
> > ATOMIC_POSITIONS {alat}
> > Fe1 0.00 0.00 0.00
> > Fe2 1.00 0.50 0.50
> > Fe3 0.50 0.50 1.00
> > Fe4 0.50 1.00 0.50
> > Mg1 0.50 0.50 0.00
> > Mg1 0.50 0.00 0.50
> > Mg1 0.00 0.50 0.50
> > Mg1 1.00 1.00 1.00
> > O1 0.50 0.00 0.00
> > O1 0.50 0.50 0.50
> > O1 1.00 0.50 0.00
> > O1 1.00 0.00 0.50
> > O1 1.50 0.50 0.50
> > O1 1.00 0.50 1.00
> > O1 1.00 1.00 0.50
> > O1 1.50 1.00 1.00
> > K_POINTS {automatic}
> > 2 2 2 0 0 0
> >
> >
> > _______________________________________________
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> >
>
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