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 ?crit : >> > >> > >> > De: Giovanni Cantele <Giovanni.Cantele at na.infn.it> >> > Objet: Re: [Pw_forum] Titanium atomic positions >> > ?: "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 Yaound? 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://www.democritos.it/pipermail/pw_forum/attachments/20090903/4fd0ffe6/attachment.htm
