[Wien] very slow SCF convergence

[Mahbube Hortamani]

Dear Wien user,

I have problem with SCF convergence of a system which is one CO molecule
on top of a (2x2) Ni surface with 68 atoms per unit cell.
The charge converges very very slow. For example, in the best case,
charge convergence after 340 iterations is just 0.002 while the energy
and magnetic moments are converged (see below). Can one trust to these 
results for
energy and magnetic moments?

grep_lapw :ITE '*scf'
:ITE328:328. ITERATION
:ITE329:329. ITERATION
:ITE330:330. ITERATION
:ITE331:331. ITERATION
:ITE332:332. ITERATION
:ITE333:333. ITERATION
:ITE334:334. ITERATION
:ITE335:335. ITERATION
:ITE336:336. ITERATION
:ITE337:337. ITERATION
:ITE338:338. ITERATION
:ITE339:339. ITERATION
:ITE340:340. ITERATION

grep_lapw :DIS '*scf'
:DIS  :  CHARGE DISTANCE       0.0019451
:DIS  :  CHARGE DISTANCE       0.0019467
:DIS  :  CHARGE DISTANCE       0.0019065
:DIS  :  CHARGE DISTANCE       0.0018985
:DIS  :  CHARGE DISTANCE       0.0019240
:DIS  :  CHARGE DISTANCE       0.0019640
:DIS  :  CHARGE DISTANCE       0.0019174
:DIS  :  CHARGE DISTANCE       0.0021151
:DIS  :  CHARGE DISTANCE       0.0023446
:DIS  :  CHARGE DISTANCE       0.0023163
:DIS  :  CHARGE DISTANCE       0.0022396
:DIS  :  CHARGE DISTANCE       0.0023006
:DIS  :  CHARGE DISTANCE       0.0020873

grep_lapw :ENE '*scf'
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101700
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101709
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101712
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101711
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101671
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101749
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101726
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101712
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101693
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101746
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101790
:ENE  : ********** TOTAL ENERGY IN Ry =      -195118.101858

grep_lapw :MMI003 '*scf'
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79119
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79119
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79121
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79125
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79129
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79133
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79157
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79167
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79167
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79167
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79167
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79166
:MMI003: MAGNETIC MOMENT IN SPHERE   3    =    0.79165

I applied following treatments to get converged charge but charge 
convergence is still slow!

1) changing the mixing factor in *.inm file for the values of 0.2, 0.05
and 0.02.
2) using "TEMP" switch with "eval 0.009 & 0.005" in *.in2 file to do E_F
and k space integration, in addition to the "TETRA" method  ( the
default setup).
3) changing muffin-tin radius of Ni.  (R_O=1 & R_C=1 & R_Ni= 2.0, 2.3)
4) changing number of Ni layers in the slab (16 & 17 layers).
5) reducing number of symmetry operations of system.
6) testing with/without CO molecule.
7) starting with very low RKmax to get *clm* and then increasing RKmax.
for small RKmax (i.e. E_cut= 6.76 Ry) convergence is faster but for
higher RKmax (E_cut= 13.66 Ry) is very slow.
8) using -in1new flag.
9) testing different Ni-C bound length (but this is not so important).

It might be helpful to know that for  bare Ni(2x2) surface, with 
E_cut=13.66 Ry, the charge converges after 280 iterations.

Does any body have experience with such problem and/or Ni surface?

P.S. this is real (not complex) and spin polarized ferromagnetic
calculation. I used WIEN2k_03 version.

Many thanks in advance,
Mahbube.


-- 
---------------------------------------------------------------------------
Mahbube Hortamani

Fritz-Haber-Institut
der Max-Planck-Gesellschaft
Abteilung Theorie
Faradayweg 4-6
D-14 195 Berlin-Dahlem / Germany

Phone  : ++49-30-8413 4820
Fax    : ++49-30-8413 4701
E-mail : hortaman at fhi-berlin.mpg.de
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