[Pw_forum] MgFeO LDA+U convergence problem

[sasha]

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