Dr. Auluck, Thanks a lot for your response. With this methodology, I end up getting a value of the order of 7 C/m^2 (as opposed to reported value of 1.29 C/m^2). So, I have been wondering about the sources of errors in my input file. A sample is copied at the end of this mail.
I studied the affect of polarization grids and they don't seem to make much difference. I am using a DZP basis set, with TM potentials for Zn and O downloaded from SIESTA database (GGA/PBE). Any other ideas on what should I be checking? Regards, Ravi ------------------------- # Input file ------------------------- # Crystal System - 6mm (Wurtzite) # Space group - P63mc # Systemname is a name for your conevenience SystemName ZnO Crystal # SystemLabel is used to name the output files accordingly SystemLabel zno NumberOfAtoms 4 NumberOfSpecies 2 MeshCutoff 350 Ry %block ChemicalSpeciesLabel 1 30 Zn # Species index, atomic number, species label 2 8 O %endblock ChemicalSpeciesLabel AtomicCoordinatesFormat Ang LatticeConstant 1.00 Ang MD.TypeofRun FC MD.NumCGsteps 300 SolutionMethod diagon PAO.BasisSize DZP PAO.BasisType split #split, splitgauss, nodes, nonodes %block PolarizationGrids 7 3 3 3 7 3 3 3 7 %endblock PolarizationGrids BornCharge True %block k_grid_Monkhorst_Pack 9 0 0 0. 0 9 0 0. 0 0 7 0 %endblock k_grid_Monkhorst_Pack maxSCFIterations 200 xc.functional GGA xc.authors PBE #for GGA - PBE, revPBE, RPBE, LYP DM.MixingWeight 0.05 DM.NumberPulay 4 DM.NumberBroyden 4 LongOutput T %block LatticeParameters 3.28430 3.28430 5.28815 90 90 60 %endblock LatticeParameters %block AtomicCoordinatesAndAtomicSpecies 1.64200 0.94825 2.64454 1 1.64200 0.94825 4.63445 2 0.00000 0.00000 0.00000 1 0.00000 0.00000 1.99040 2 %endblock AtomicCoordinatesAndAtomicSpecies On Fri, Dec 5, 2008 at 9:53 PM, Sushil Auluck <[EMAIL PROTECTED]> wrote: > ravi, > you are correct. make sure volume is in m^3...... > s.auluck > > > Dear SIESTA users, > > > > I am trying to do the calculation of piezoelectric coefficients for bulk > > ZnO > > with a unit cell consisting of 4 atoms. > > Coefficient (d33) is calculated as the slope of polarization vs strain > > curve. Strain is dimensionless and therefore the units of d33 is same as > > that of polarization. > > > > In SIESTA output, the polarization is expressed in Debye units (1 Debye = > > 3.33 X 10e-30 C-m). To convert it to C/m^2 (standard unit used for d33), > I > > am diving by the volume of the unit cell. Is that correct or am I missing > > something? > > > > Thanks in advance. > > > > Ravi > > > > > ....................................................................... > Prof. Sushil Auluck Phone:+91-512-6797092/6148 > Department of Physics +91-512-6798177(Home) > Indian Institute of Technology Cell :+91-9305548667 > Kanpur 208016 (UP) Fax :+91-512-6790914 > India E-mail:[EMAIL PROTECTED]<[EMAIL > PROTECTED]> > ...............................................:[EMAIL PROTECTED] > http://www.iitk.ac.in/phy/People/phy_facvis.html > http://www.iitk.ac.in/phy/New01/profile_SA.html > ....................................................................... > ~ >
