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
--- 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
?***********************
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