[Pw_forum] Titanium atomic positions
udayagiri sai babu
udayagiri3 at gmail.com
Wed Sep 2 20:52:29 CEST 2009
i am sorry for the previous message which i could not type completely.T his
is what i mean
for the ATOMIC_POSITIONS if you choose "crystal" your lattice coordinates
are correct
Ti 0.3333 0.6666 0.2500
Ti 0.6666 0.3333 0.7500
or else you can represent same as
ATOMIC_POSITIONS (crystal)
Ti 0 0 0
Ti 0.333333 0.666666 0.500000
both are same except they are displaced by (1/3,2/3,1/4)
On Thu, Sep 3, 2009 at 12:18 AM, udayagiri sai babu <udayagiri3 at gmail.com>wrote:
> for the ATOMIC_POSITIONS if you choose "crystal" your lattice coordinates
> are correct
> Ti 0.3333 0.6666 0.2500
> Ti 0.6666 0.3333 0.7500
>
> or else you can represent same as
> ATOMIC_POSITIONS (crystal)
> Ti 0 0.2500
> Ti 0.6666 0.3333 0.7500
>
> On Wed, Sep 2, 2009 at 9:28 PM, Giovanni Cantele <
> Giovanni.Cantele at na.infn.it> wrote:
>
>> Bertrand SITAMTZE wrote:
>> > Dear Giovanni,
>> >
>> > My coordinates are those taken from 2c position of
>> > the crystallographic space group table. I though these correspond to
>> > the default (alat) in quantum espresso,
>> > in which case mentioning is not mandatory. Isn't it?
>> >
>> > Thanks once more
>> >
>>
>> It is not mandatory to specify the default, but I'm not very sure that
>> your coordinates are in alat units. From
>> http://cst-www.nrl.navy.mil/lattice/struk/a3.html
>> I understand that (1/3,2/3,1/4) and (2/3,1/3,3/4) are in terms of the
>> A1, A2 and A3 vectors rather than
>> the x, y z axes versors. alat positions are cartesian coordinates (in
>> unit of celldm(1)), which are the same as crystal coordinates only for a
>> simple cubic lattice.
>>
>> If I'm not wrong, as pointed out by someone else, you should check that
>> the A1, A2, A3 choice shown in the
>> above link is the same as in Quantum-ESPRESSO (for the latter please
>> have a look to Doc/INPUT_PW* ). If not, you may specify your own lattice
>> vectors by using the CELL_PARAMETERS card.
>>
>> Giovanni
>>
>>
>> >
>> > --- En date de : *Mer 2.9.09, Giovanni Cantele
>> > /<Giovanni.Cantele at na.infn.it>/* a écrit :
>> >
>> >
>> > De: Giovanni Cantele <Giovanni.Cantele at na.infn.it>
>> > Objet: Re: [Pw_forum] Titanium atomic positions
>> > À: "PWSCF Forum" <pw_forum at pwscf.org>
>> > Date: Mercredi 2 Septembre 2009, 16h48
>> >
>> > Beside the check of the hcp unit cell, which is crucial, I also
>> guess
>> > that you gave the input positions
>> > in "crystal" units, didn't you? If it is the case, I think that you
>> > should add the "{ crystal }" string after ATOMIC_POSITIONS.
>> > Indeed, the
>> > default is "alat" units, I think, namely, cartesian coordinates in
>> > celldm(1) units.
>> >
>> > Also do not forget to check the convergence of your results with
>> > respect
>> > to ecutrho. The default value (4*ecutwfc) must be usually
>> > increased (6
>> > to 12 times ecutwfc) if, as in you case, ultrasoft
>> > pseudopotentials are
>> > used.
>> >
>> > Giovanni
>> >
>> >
>> > Hande Ustunel wrote:
>> > > Dear Bertrand,
>> > >
>> > > Your atomic positions are rather off with a large gap between
>> > rumpled Ti
>> > > layers. Perhaps you should double-check that your definition of
>> > the hcp
>> > > unit cell matches that for ibrav=4 in the code. You can find this
>> > > information in the Doc directory in your copy of espresso.
>> > >
>> > > Besides, you should be able to check your structure for yourself
>> > using
>> > > xcrysden (--pwi option).
>> > >
>> > > Best wishes,
>> > > Hande
>> > >
>> > > On Wed, 2 Sep 2009, Bertrand SITAMTZE wrote:
>> > >
>> > >
>> > >> Dear all,
>> > >>
>> > >> Titanium belongs to the hexagonal P63/mmc
>> > >> (n° 194) space group. I would like somebody to confirm that my
>> > attached
>> > >> input section concerning the bravais lattice and specially the
>> > atomic positions are good.
>> > >>
>> > >> &SYSTEM
>> > >> ibrav=4
>> > >> celldm(1)=5.576203
>> > >> celldm(3)=1.587874
>> > >> nat=2
>> > >> ntyp=1
>> > >> ecutwfc=40.0
>> > >> /
>> > >> &ELECTRONS
>> > >> diagonalization='cg'
>> > >> /
>> > >> ATOMIC_SPECIES
>> > >> Ti 47.867 Ti.pw91-nsp-van.UPF
>> > >> ATOMIC_POSITIONS
>> > >> Ti 0.3333 0..6666 0.2500
>> > >> Ti 0.6666 0.3333 0.7500
>> > >> K_POINTS automatic
>> > >> 8 8 4 0 0 0
>> > >>
>> > >>
>> > >> Best regards
>> >
>> > *********************
>> > Bertrand SITAMTZE
>> > PhD student
>> > Department of Physics
>> > University of Yaoundé I-Cameroon
>> > ***********************
>> >
>> >
>> > ------------------------------------------------------------------------
>> >
>> > _______________________________________________
>> > Pw_forum mailing list
>> > Pw_forum at pwscf.org
>> > http://www.democritos.it/mailman/listinfo/pw_forum
>> >
>>
>>
>> --
>>
>>
>>
>> Dr. Giovanni Cantele
>> Coherentia CNR-INFM and Dipartimento di Scienze Fisiche
>> Universita' di Napoli "Federico II"
>> Complesso Universitario di Monte S. Angelo - Ed. 6
>> Via Cintia, I-80126, Napoli, Italy
>> Phone: +39 081 676910
>> Fax: +39 081 676346
>> E-mail: giovanni.cantele at cnr.it
>> giovanni.cantele at na.infn.it
>> Web: http://people.na.infn.it/~cantele<http://people.na.infn.it/%7Ecantele>
>> Research Group: http://www.nanomat.unina.it
>> Skype contact: giocan74
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
>>
>
>
>
> --
> U.Saibabu
> PhD student,
> Deformation mechanisms modeling group,
> Materials engineering department,
> IISc Bangalore,
> India.
>
>
--
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20090903/4fd0ffe6/attachment.html>
More information about the users
mailing list