[Wien] Relaxation (mini) problem

[Lukasz Plucinski]

Dear WIEN Users,

I have a problem with relaxation of forces. Let,s use InGaN as an example
- this is a simplest unit cell for InGaN with 50% of Ga replaced by In
(x=0.5), 'optimized' atomic positions from struct file are at the end of
this e-mail. This is inM file for mini:

NEWT 2.0           #(NOSE, NEWT, BFGS, MOLD, tolf (a4,f5.2))
0.0 0.0 0.0 0.2    # Atom1   (NOSE, MOLD:Masse, delta t, T, nose-frequency)
0.2 0.2 0.2 0.2    # Atom2   (NEWT: 1,2,3:delta, 4:eta(1=MOLD))
0.2 0.2 0.2 0.2    # Atom3   (BFGS, NEWT: [ 1 || 2 || 3 ] = 0 constraint)
0.2 0.2 0.2 0.2

These are forces at the end of scf_mini file:

       TOTAL FORCE IN mRy/a.u. = |F|     Fx             Fy             Fz
:FOR001:   1.ATOM         14.750          0.000          0.000         14.750
:FOR002:   2.ATOM          0.847          0.000          0.000         -0.847
:FOR003:   3.ATOM          1.809          0.000          0.000         -1.809
:FOR004:   4.ATOM          1.301          0.000          0.000         -1.301

I didn't move atom #1 because I guess its only necessary to move 3 atoms
when there are 4 in the supercell but then the force on the atom #1 is not
optimized (its 14.750). Why it is the case?

In this particular case it doens't matter much because one can of course
move atom #1 without losing much time (it was moved in the previous
optimization runs on this unit cell - that's why its 'z' position is
0.97398187). However, I noticed that similar things happen when relaxaing
the surface with typical 3 layers relaxation - I don't like this because
it means its a lot of strain when 3 layers are relaxed and one should
maybe relax many more layers - this puts in question surface BS calculated
later with such relaxation.

Please help!

Regards,

Lukasz


PS. To ML-administrator: this time I use again my original e-mail
plucinks at mail.desy.de to send this e-mail to the mailing list. When I use
my new e-mail pluto at physics.bu.edu I always have to wait for the
'moderator' decision - maybe its related to the fact that 'physics.bu.edu'
is alias of 'buphy.bu.edu'?

Atomic postions from struct file:

ATOM  -1: X=0.00000000 Y=0.00000000 Z=0.97398187
          MULT= 1          ISPLIT= 4
In1        NPT=  781  R0=.000100000 RMT=   1.60000   Z:  49.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -2: X=0.33333334 Y=0.66666666 Z=0.44446940
          MULT= 1          ISPLIT= 4
Ga1        NPT=  781  R0=.000100000 RMT=   1.60000   Z:  31.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -3: X=0.00000000 Y=0.00000000 Z=0.32733882
          MULT= 1          ISPLIT= 4
N 1        NPT=  781  R0=.000100000 RMT=   1.60000   Z:   7.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM  -4: X=0.33333334 Y=0.66666666 Z=0.88009706
          MULT= 1          ISPLIT= 4
N 2        NPT=  781  R0=.000100000 RMT=   1.60000   Z:   7.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000