[Wien] accuracy problem after running x sgroup

[Peter Blaha]

Then it simply means, that after min_lapw your atoms arrived at 
positions, which made them nearly equivalent, so that sgroup does not 
know within its accuracy limits if two atoms are equivalent or not.

Eventually "correct" positions manually, eg. setting atoms at
0.50002 to 0.50000  and so on.

Am 23.10.2010 08:42, schrieb shamik chakrabarti:
> Dear Peter Blaha Sir,
>                                I am using wien2k_08. No it is not an
> hexagonal lattice. Actually the space group is unknown. We have taken a
> structure A2BCO4 which has space group Pnma and then *replace atom C
> with atom D *considering *primitive space group*. We have used the
> atomic coordinates and lattice constants of A2BCO4. But we have made all
> the atoms inequivalent in the new material A2BDO4 by considering
> primitive space group. It was done as we *do not want to include the
> symmetry constraints* for the atoms of this new material as A2BDO4 may
> have some different structure than A2BCO4. We want to see if A2BDO4
> structure is feasible or not and infact DFT has found a structure with
> minimum energy and minimum force on the atoms.
>
> with best regards,
> Shamik Chakrabarti
> On Sat, Oct 23, 2010 at 11:48 AM, Peter Blaha
> <pblaha at theochem.tuwien.ac.at <mailto:pblaha at theochem.tuwien.ac.at>> wrote:
>
>     Are you using WIEN2k_10 ???  It should not happen anymore.
>
>     Hexagonal lattice ???  min_lapw could have produced atomic
>     positions, which are not completely equivalent anymore (like
>     0.3333333 and 0.666666) because of rounding errors.
>
>     Check your atomic positions manually.
>
>     Am 23.10.2010 06:22, schrieb shamik chakrabarti:
>
>         Dear wien2k users,
>
>                                      we have done structure optimization
>         (both
>         volume and force) of a A2BCO4 type material. After optimization the
>         maximum force on an atom is *2.036 mRy/a.u.* After optimization
>         if we
>         view the structure with xcrysden we can see that some atoms remain
>         unbonded i.e. one or two free atom and the rest of the structure is
>         connected through bond. Now my questions are:
>
>                    (1) Can such a structure be stable although DFT has
>         able to
>         found a solution in which the energy of the unit cell and forces
>         on the
>         atoms are minimum?
>
>                    (2) When I take this optimized struct file and tried to
>         initilize and run a SCF with this struct file, after *x sgroup*
>         command
>         it will show :
>         *Accuracy problem. Please run with different tolerance (x sgroup
>         -settol
>         .00000100)*
>         *
>         *
>                        Now if we ignore this problem or we run the command x
>         sgroup -settol 0.00000100, irrespective of that all the atoms got
>         deleted after x symmetry command!!
>
>                        So, my question is whether this optimized struct
>         file is
>         not feasible or is their any way to remove this accuracy problem?
>
>         any response will be very helpful for us. Thanking you,
>
>         with regards,
>
>
>         --
>         Shamik Chakrabarti
>         Research Scholar
>         Dept. of Physics & Meteorology
>         Material Processing & Solid State Ionics Lab
>         IIT Kharagpur
>         Kharagpur 721302
>         INDIA
>
>
>
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>
>
>     --
>     Peter Blaha
>     Inst.Materials Chemistry
>     TU Vienna
>     Getreidemarkt 9
>     A-1060 Vienna
>     Austria
>     +43-1-5880115671
>     _______________________________________________
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>     http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>
>
>
> --
> Shamik Chakrabarti
> Research Scholar
> Dept. of Physics & Meteorology
> Material Processing & Solid State Ionics Lab
> IIT Kharagpur
> Kharagpur 721302
> INDIA
>
>
>
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-- 
Peter Blaha
Inst.Materials Chemistry
TU Vienna
Getreidemarkt 9
A-1060 Vienna
Austria
+43-1-5880115671