[Pw_forum] MgFeO LDA+U convergence problem

[Matteo Cococcioni]

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
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>   

-------------- next part --------------
A non-text attachment was scrubbed...
Name: matteo.vcf
Type: text/x-vcard
Size: 294 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20070514/212c5ee6/attachment.vcf>