[Pw_forum] SCF convergency

[Jun-jun Yang]

Dear list users,

I'm working on scf calculation of mineral chromite. I think the calculation 
may be on the right
track but I still have problem on its convergency. The accuracy alway 
osillates between about
1.5e-5 and 1 (Ry) after 10th iteration (100 in total) although the lower 
value had nearly reached
the convergence threshold conv_thr = 1.0d-5. I have tried other two 
minimization algorithms
(david and diis), and it seems that the result with cg is the best.

My co-worker is trying to do the same calculation with CPMD (v3.9.2). He did 
electron annealing
first to bring the total energy to a would-be global(?) minima, then switch 
to scf calculation using
diis or cg with preconditioning. Unfortunately, he got very similar system 
behaviour with mine.

As my next step, I prepare to set conv_thr = 5.0e-5 and continue my 
calculation with different
a0, then use the Etot - volume data to fit an EOS and compare the result 
with other experimental
data. This could tell me if the calculations are reasonable. As both my 
co-worker and I are beginers
of the relevant software, and the calculations are very time-consumming, 
before I proceed to my
next step, I ask your help to see whether I made anything wrong in the 
input, or let me know if I
need to do this or that for correct practice.


Best regards and thanks in advance.


Yang Jun-jun


Below is the snippet of my input file:
===================================
&control
   calculation = 'scf'
   restart_mode='from_scratch'
   prefix='fecr2o4'
   tstress = .false.
   tprnfor = .false.
   pseudo_dir = '$HOME/espresso-2.1.5/pseudo'
   outdir = $HOME/tmp/
   wf_collect = .true.
/
&system
    ibrav = 1, celldm(1) = 15.8321, nat = 56, ntyp = 3
    nbnd = 330
    nspin = 2, degauss = 0.5
    occupations = 'smearing'
    smearing = 'gaussian'
    starting_magnetization(1) = 0.0
    ecutwfc = 25.0
    ecutrho = 140.0
/
&electrons
    diagonalization = 'cg'
    mixing_mode = 'plain'
    mixing_beta = 0.40
    conv_thr = 1.0d-5
/

ATOMIC_SPECIES
Fe  55.847	Fe.pbe-sp-van.UPF
Cr  51.996	Cr.pbe-sp-van.UPF
O   15.999	O.pbe-van_ak.UPF

ATOMIC_POSITIONS angstrom
Fe    0.00000	 0.00000    0.00000
Cr    5.23625	 5.23625    5.23625
O    3.23391	 3.23391    3.23391
Fe    0.00000	 4.18900    4.18900
Fe    4.18900	 0.00000    4.18900
[...]

K_POINTS automatic
1 1 1 0 0 0


I have sent this mail three times with a graph attached. The first two posts 
had been rejected
because size of the mail was a little larger than the limit. The third one 
should be below 40KB,
but I haven't seen its appearing on the list yet. So, I have to post it 
again without a graph. I
apologize for that you may receive two mails with similar content.

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