[Pw_forum] Titanium atomic positions

[udayagiri sai babu]

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
> >      ***********************
> >
> >
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
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> >
>
>
> --
>
>
>
> 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
>
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-- 
U.Saibabu
PhD student,
Deformation mechanisms modeling group,
Materials engineering department,
IISc Bangalore,
India.
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