Thanks Eric. On Wed, Mar 9, 2011 at 5:19 AM, Eric Germaneau <[email protected]>wrote:
> Here we are. > I'm sorry I did not perform such simulation with Siesta. > At room temperature b-cristobalite turns to the metastable form > a-cristobalite (no longer cubic). > Silica is a very interesting mess. > Good luck. > > Eric. > > > On 03/08/2011 06:12 PM, Prathibha Ramaprasad wrote: > > 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. * >> > > > -- > * 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. * >
