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. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090903/f4c632e2/attachment-0001.htm
