[Pw_forum] BFGS convergence

[PRASENJIT GHOSH]

Dear all,

I'm trying to relax 4layer MgO(100) surface with IML Rh atom & NO on it.
I'm keeping the bottom 2 layers fixed & relaxing rest of the layers along
all directions. I have set forc_conv_thr as 5.0D-4. When the BFGS
optimization is complete the total force printed out is 0.001184 Ry/au.,
which is higher than the threshold.

The force on individual atoms are as given below:

     atom   1 type  4   force =     0.00000000    0.00019439    0.00035388
     atom   2 type  2   force =     0.00000000    0.00003994    0.00030581
     atom   3 type  3   force =     0.00004990    0.00006395    0.00026932
     atom   4 type  3   force =    -0.00004990    0.00006395    0.00026932
     atom   5 type  3   force =     0.00000510   -0.00010716    0.00017645
     atom   6 type  3   force =    -0.00000510   -0.00010716    0.00017645
     atom   7 type  3   force =    -0.00015740    0.00021421    0.00025840
     atom   8 type  3   force =     0.00015740    0.00021421    0.00025840
     atom   9 type  1   force =     0.00000000    0.00017531    0.00012835
     atom  10 type  1   force =     0.00000000    0.00012586    0.00009343
     atom  11 type  2   force =    -0.00003854   -0.00009570   -0.00010196
     atom  12 type  2   force =     0.00003854   -0.00009570   -0.00010196
     atom  13 type  1   force =     0.00000000    0.00002684    0.00020808
     atom  14 type  1   force =     0.00000000   -0.00008463    0.00035348
     atom  15 type  2   force =    -0.00002782   -0.00001293    0.00001952
     atom  16 type  2   force =     0.00002782   -0.00001293    0.00001952
     atom  17 type  1   force =     0.00000000    0.00001629    0.00009910
     atom  18 type  1   force =     0.00000000   -0.00003038    0.00014986
     atom  19 type  2   force =     0.00000763    0.00008195    0.00007784
     atom  20 type  2   force =    -0.00000763    0.00008195    0.00007784
     atom  21 type  2   force =     0.00000000    0.00003195    0.00010070
     atom  22 type  2   force =     0.00000000    0.00003854    0.00016380
     atom  23 type  1   force =    -0.00010405   -0.00006846    0.00012527
     atom  24 type  1   force =     0.00010405   -0.00006846    0.00012527
     atom  25 type  2   force =     0.00000000   -0.00002769    0.00001703
     atom  26 type  2   force =     0.00000000   -0.00007519    0.00008055
     atom  27 type  1   force =    -0.00004277    0.00010317   -0.00017790
     atom  28 type  1   force =     0.00004277    0.00010317   -0.00017790
     atom  29 type  2   force =     0.00000000    0.00001178    0.00015564
     atom  30 type  2   force =     0.00000000    0.00009848    0.00005032
     atom  31 type  1   force =    -0.00009405   -0.00007765    0.00004686
     atom  32 type  1   force =     0.00009405   -0.00007765    0.00004686
     atom  33 type  1   force =     0.00000000   -0.00027438   -0.00258973
     atom  34 type  1   force =     0.00000000    0.00085927   -0.00230357
     atom  35 type  2   force =    -0.00002762    0.00106477    0.00266372
     atom  36 type  2   force =     0.00002762    0.00106477    0.00266372
     atom  37 type  1   force =     0.00000000   -0.00127835   -0.00262410
     atom  38 type  1   force =     0.00000000   -0.00187757   -0.00264360
     atom  39 type  2   force =     0.00033189   -0.00088088    0.00323964
     atom  40 type  2   force =    -0.00033189   -0.00088088    0.00323964
     atom  41 type  1   force =     0.00000000    0.00132099   -0.00267980
     atom  42 type  1   force =     0.00000000    0.00088146   -0.00307944
     atom  43 type  2   force =     0.00043540   -0.00046399    0.00208586
     atom  44 type  2   force =    -0.00043540   -0.00046399    0.00208586
     atom  45 type  2   force =     0.00000000   -0.00001967   -0.01458796
     atom  46 type  2   force =     0.00000000    0.00001272   -0.01458917
     atom  47 type  1   force =    -0.00001307   -0.00005348    0.01390984
     atom  48 type  1   force =     0.00001307   -0.00005348    0.01390984
     atom  49 type  2   force =     0.00000000   -0.00068276   -0.01433952
     atom  50 type  2   force =     0.00000000   -0.00070884   -0.01425615
     atom  51 type  1   force =     0.00001464   -0.00004340    0.01348247
     atom  52 type  1   force =    -0.00001464   -0.00004340    0.01348247
     atom  53 type  2   force =     0.00000000    0.00075245   -0.01418097
     atom  54 type  2   force =     0.00000000    0.00074367   -0.01430795
     atom  55 type  1   force =     0.00003199    0.00014034    0.01388566
     atom  56 type  1   force =    -0.00003199    0.00014034    0.01388566

     Total force =     0.001184     Total SCF correction =     0.000147


Atoms 33-56 are kept fixed. Hence the forces on them is high whereas the
forces on each of the individual components of the relaxed atoms are below
the threshold.

My question is when the code calculates the force (grad) & their
differencec between 2 consecutive BFGS iter. (grad_error) & is it only for
the atoms which are allowed to relax or for the full system or something
is going wrong in the calculation? I'm using version 3.0.

With regards,
Prasenjit.

PRASENJIT GHOSH,
Ph. D STUDENT,
THEORETICAL SCIENCES UNIT,
JAWAHARLAL NEHRU CENTRE,
JAKKUR P. O.,
BANGALORE - 560064,
INDIA.

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