Hi Eric, Appreciate it if you can send me your cif file. Did you by any chance use Wychoff or Barth version? Also if you have done a similar calculation on siesta, do you mind sending me the fdf input file as well. I am having a real puzzled time with it.
Thank you very much for your help. Prat On Wed, Mar 9, 2011 at 4:51 AM, Eric Germaneau <[email protected]>wrote: > Hey Prat, > > b-cristobalite lattice parameter is 7.16 experimentally and it's stable at > high temperature (above ~1770K). > I can send you the cif file I usually use for this system. > > Eric. > > > On 03/08/2011 05:28 PM, Prathibha Ramaprasad wrote: > > Dear Siesters, > > I am working with b-cristobalite, a silica polymorph. I am puzzled by two > different equilibrium lattice constant i obtain using a 2-atom primitive > cell (7.14A) and a 24-atom one complete unit cell (7.57A). Maybe I doing > something fundamentally wrong, appreciate if anyone can point out the error. > > Here's my fdf for 2atom version: > SystemName b-cristobalite > SystemLabel bcris_7.14A > NumberOfAtoms 2 > NumberOfSpecies 2 > %block ChemicalSpeciesLabel > 1 14 Si.gga > 2 8 O.gga > %endblock ChemicalSpeciesLabel > LatticeConstant 7.14 Ang > %block LatticeParameters > 1.0 1.0 1.0 90. 90. 90. > %endblock LatticeParameters > BandLinesScale pi/a > %block BandLines > 1 1.5 1.5 0.0 K # Begin at K > 38 0.0 0.0 0.0 \Gamma # 38 points from K to Gamma > 36 0.0 2.0 0.0 X # 36 points from Gamma to X > 18 1.0 2.0 0.0 W # 18 points from X to W > 26 1.0 1.0 1.0 L # 26 points from W to L > 31 0.0 0.0 0.0 \Gamma # 31 points from L to Gamma > %endblock BandLines > AtomicCoordinatesFormat Fractional > %block AtomicCoordinatesAndAtomicSpecies > 0.000 0.000 0.000 1 Si > 0.125 0.125 0.125 2 O > %endblock AtomicCoordinatesAndAtomicSpecies > %block kgrid_Monkhorst_Pack > 4 0 0 0.5 > 0 4 0 0.5 > 0 0 4 0.5 > %endblock kgrid_Monkhorst_Pack > XC.functional GGA > XC.authors PBE > PAO.BasisSize DZP > PAO.EnergyShift 300 meV > MeshCutoff 100. Ry > > and for the 24 atom version, I only change the add the extra coordinates: > AtomicCoordinatesFormat Fractional > %block AtomicCoordinatesAndAtomicSpecies > 0.125 0.125 0.125 2 O1 1 > 0.125 0.625 0.625 2 O2 2 > 0.625 0.625 0.125 2 O3 3 > 0.625 0.125 0.625 2 O4 4 > 0.125 0.875 0.875 2 O5 5 > 0.125 0.375 0.375 2 O6 6 > 0.625 0.375 0.875 2 O7 7 > 0.625 0.875 0.375 2 O8 8 > 0.875 0.125 0.875 2 O9 9 > 0.875 0.625 0.375 2 O10 10 > 0.375 0.625 0.875 2 O11 11 > 0.375 0.125 0.375 2 O12 12 > 0.875 0.875 0.125 2 O13 13 > 0.875 0.375 0.625 2 O14 14 > 0.375 0.375 0.125 2 O15 15 > 0.375 0.875 0.625 2 O16 16 > 0 0 0 1 Si1 17 > 0 0.5 0.5 1 Si2 18 > 0.5 0.5 0 1 Si3 19 > 0.5 0 0.5 1 Si4 20 > 0.25 0.25 0.25 1 Si5 21 > 0.25 0.75 0.75 1 Si6 22 > 0.75 0.75 0.25 1 Si7 23 > 0.75 0.25 0.75 1 Si8 24 > %endblock AtomicCoordinatesAndAtomicSpecies > > Thank you for your time, > Prat > > > -- > * Be the change you wish to see in the world > * — Mahatma Gandhi — > > Dr. Éric Germaneau <[email protected]> > > College of Physical Sciences > Graduate University of Chinese Academy of Sciences > Yuquan Road 19A > Beijing 100049 > China > > * Please consider the environment before printing this email. > Considérez svp l'environnement avant d'imprimer cet email. * >
