[Wien] accuracy problem after running x sgroup
shamik chakrabarti
shamikphy at gmail.com
Tue Oct 26 11:06:32 CEST 2010
Dear Peter Blaha Sir and wien2k users,
We have implemented your suggestion and was
able to remove the space group tolerence problem. But still I have a
question regarding the structure. In the energy and force optimized
structure there are some atomic networks and atoms which are not bonded with
each other. The networks and atoms are remain disconnected with the main
atomic network. If we repeat the unit cell along x, y and z direction, some
networks get bonded but still there remain some free networks and atoms.
Thise happened as we replaced C atom in A2BCO4 by D atom. Due to this
replacement lattice parameter enhances but the space group symmetry remains
same. Hence the atoms which remain bonded in A2BCO4 separated much from each
other and get unbonded in A2BDO4. *Now my question is this types of unbonded
atomic structure is really feasible although the energy and force are
minimum in that structure??....*
In some experimentally generated pure phase structure also we have seen such
unbonded atoms and atomic network. As they are already experimentally
prepared they are feasible although in the unit cell some atoms can be shown
to be remaind unbonded. *Then how can we explain the presence of the
unbonded atomic networks in this experimentally prepared materials??...*
*
*
*with best regards,*
*Shamik Chakrabarti
*
On Sat, Oct 23, 2010 at 12:21 PM, shamik chakrabarti <shamikphy at gmail.com>wrote:
> Dear Peter Blaha Sir,
>
> Thank you very much for your reply. I have
> understand what you have said and will try to implement the same. Yes it
> should solve the problem. Thank you sir, thank you very much!!....
>
> with best regards,
> Shamik Chakrabarti
>
>
> On Sat, Oct 23, 2010 at 12:17 PM, Peter Blaha <
> pblaha at theochem.tuwien.ac.at> wrote:
>
>> 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
>>>
>>>
>>>
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> <mailto:Wien at zeus.theochem.tuwien.ac.at>
>>>
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>>
>>>
>>> --
>>> Peter Blaha
>>> Inst.Materials Chemistry
>>> TU Vienna
>>> Getreidemarkt 9
>>> A-1060 Vienna
>>> Austria
>>> +43-1-5880115671
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at <mailto:
>>> Wien at zeus.theochem.tuwien.ac.at>
>>>
>>> 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
>>>
>>>
>>>
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>>
>>
>> --
>> Peter Blaha
>> Inst.Materials Chemistry
>> TU Vienna
>> Getreidemarkt 9
>> A-1060 Vienna
>> Austria
>> +43-1-5880115671
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> 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
>
--
Shamik Chakrabarti
Research Scholar
Dept. of Physics & Meteorology
Material Processing & Solid State Ionics Lab
IIT Kharagpur
Kharagpur 721302
INDIA
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