[Wien] Geometry optimization: constraint failed?

[Oleg Rubel]

Dear Wien2k Users and Developers,

I calculate desorption of a dimer from a surface of III/V semiconductor using WIEN2k_08.3 (Release 18/9/2008). In this calculation, I would like to restrict the dimer from motion in Z direction perpendicular to the surface, though allow the atom to move in X-Y plane while searching for the lowest energy. To achieve this behaviour, I set up the *.inM file in the following way:

    $ cat *.inM
    PORT 2.0 0.35      # PORT/NEWT;  tolf, Initial Trust Radius
    1.0 1.0 1.0 1.0   #Atom    1 Generated by pairhess
    1.0 1.0 1.0 1.0   #Atom    2 Generated by pairhess
    ...
    1.0 1.0 0.0 1.0   #Atom  112 Generated by pairhess
    ...

Here atom 112 is one of two atoms in the dimer. But, after running "mini" I have got:

    $ grep :POS112 *scf_mini
    :POS112: AT.NR.-112 POSITION = 0.68430 0.32271 0.95580  MULTIPLICITY =  1
    :POS112: AT.NR.-112 POSITION = 0.68654 0.32342 0.95523  MULTIPLICITY =  1
    ...
    :POS112: AT.NR.-112 POSITION = 0.71314 0.32367 0.95252  MULTIPLICITY =  1
    ...
    :POS112: AT.NR.-112 POSITION = 0.76567 0.32632 0.94984  MULTIPLICITY =  1

Obviously, the Z coordinate changes during mini. My lattice is primitive:

    $ cat *.struct
    ...
    P                          114 1 P1
                 RELA
     15.004806 30.009612 52.652500 90.000000 90.000000 90.000000
    ...

With this lattice size, the atom 112 was shifted in Z direction by 0.3 bohr during "mini"!

My question is: Did I misinterpret the content of the *.inM file? How can I FIX Z coordinate and let X and Y to change?

As a note: Setting "0.0 0.0 0.0 0.0   #Atom   63" does results in a desired behaviour when I want to fix atom 63 completely.

Any suggestion are highly welcome.

Thank you in advance,

Oleg Rubel 

--
Oleg Rubel, PhD
Scientist
Thunder Bay Regional Research Institute
290 Munro St
Thunder Bay, ON
P7A  7T1, Canada
Phone: +1-807-7663350
Fax: +1-807-3441948
E-mail: rubelo at tbh.net
Homepage: http://www.tbrri.com/~orubel/