Is this perovskite ferroelectric? If so you could calculate the polarization along the switching path (even if it does not go through a high symmetry phase) to get a meaningful value of P.
Pablo On Tue, Oct 1, 2013 at 3:20 PM, Andrei Buin <[email protected]> wrote: > Thank you Pablo. The problem is this particular pervoskite does not have a > centrosymmetric phase. I do realize that polarization is defined modulo x > (since momentum operator defined modulo x), then i have to a have reference > phase(which i dont). Thanks for the corrections for the PolarizationGrid > block. Will try it. > > With Best Regards, Andrei Buin. > > > > On Tue, Oct 1, 2013 at 9:13 AM, Pablo Aguado <[email protected]> wrote: > >> >> Hi Andrie, >> >> A couple of comments, first the absolute value of the polarization per se >> is only defined modulo a quantum of polarization, so the value you get is P >> = P_"real" + n P_q, where n is an integer number and P_q is the quantum of >> polarization. P_q=e/A where A is the surface area of your unit cell >> perpendicular to the direction with respect to which you are calculating P. >> >> Since you don't know the value of n, to get the value of P_"real" you >> usually calculate the polarization of a reference structure which P is >> known by symmetry (in perovskites for instance, the centrosymetric phase >> has either 0 or P_q/2). Then substracting the P from the centrosymmetric >> you should be able to get the polarization of the polar phase (you might >> still have some problems to identify the "true" polarization if the P of >> the polar phase is comparable or larger than the quantum, see this >> introductory paper for more details http://arxiv.org/abs/1202.1831) >> >> Another issue is the PolarizationGrid block you are using, which is the >> example in the siesta manual and might not be the most suitable for you >> simulation cell. Something like this would make more sense (re-read the >> manual entry for the meaning of this block): >> >> %block PolarizationGrids >> 20 4 4 yes >> 4 20 4 yes >> 4 4 15 yes >> %endblock PolarizationGrids >> >> Best regards, >> >> Pablo >> >> >> On Tue, Oct 1, 2013 at 2:39 PM, Andrei Buin <[email protected]> wrote: >> >>> Dear Siesta forum, >>> >>> I have 48(pervoskite CH3NH3PbI3) atoms in the 9 Angs x 9 Angs x 12 Angs >>> unit cell. >>> I'm trying to compute the Berry phase polarization usign >>> PolarizationGrids, and i get >>> insane dipole moment of: >>> >>> siesta: Macroscopic polarization per unit cell (Debye): >>> siesta: Along the lattice vectors 2742.652644 2679.284584 4191.471845 >>> siesta: Along cartesian directions 2742.652644 2679.284584 4191.471845 >>> >>> >>> >>> Input is attached. Forces are already converged. >>> >>> # 6.2 General System descriptors >>> >>> SystemName Tetra Super Unit Cell Siesta Calculations >>> SystemLabel Tet # Short name for naming files >>> NumberOfSpecies 5 >>> NumberOfAtoms 48 >>> >>> %block Chemical_Species_Label >>> 1 82 Pb >>> 2 53 I >>> 3 7 N >>> 4 6 C >>> 5 1 H >>> %endblock Chemical_Species_Label >>> >>> >>> >>> >>> # 6.3 Basis definitions >>> >>> PAO.BasisSize DZP >>> PAO.EnergyShift 65 meV >>> #PAO.SplitNorm 0.15 >>> PAO.SplitTailNorm true >>> PAO.SoftDefault true >>> PAO.OldStylePolOrbs false >>> >>> %block PS.KBprojectors >>> I 4 >>> 0 2 >>> 2000 -2000 >>> 1 2 >>> 2000 -2000 >>> 2 2 >>> 2000 -2000 >>> 3 1 >>> 2000 >>> >>> >>> Pb 4 >>> 0 2 >>> 2000 -2000 >>> 1 2 >>> 2000 -2000 >>> 2 2 >>> 2000 -2000 >>> 3 1 >>> 2000 >>> >>> N 4 >>> 0 2 >>> 2000 -2000 >>> 1 2 >>> 2000 -2000 >>> 2 2 >>> 2000 -2000 >>> 3 1 >>> 2000 >>> >>> H 3 >>> 0 2 >>> 2000 -2000 >>> 1 2 >>> 2000 -2000 >>> 2 1 >>> 2000 >>> >>> C 4 >>> 0 2 >>> 2000 -2000 >>> 1 2 >>> 2000 -2000 >>> 2 2 >>> 2000 -2000 >>> 3 1 >>> 2000 >>> %endblock PS.KBprojectors >>> >>> >>> >>> %block PAO.Basis # Define Basis set >>> Pb 3 # Species label, number of l-shells >>> n=6 0 2 # n, l, Nzeta, Polarization, NzetaPol >>> 0 0 >>> n=6 1 2 P 1 # n, l, Nzeta, Polarization, >>> NzetaPol >>> 0 0 >>> n=5 2 1 # SZ for 5d >>> 0 #0 >>> >>> >>> # H in C6H6 DZP >>> #Vova >>> H 2 0.00000 >>> n=1 0 2 E 11.36136 0.00928 >>> 7.72405 2.19949 >>> n=2 1 1 E 41.15301 0.00947 >>> 2.89938 >>> >>> >>> # C in C6H6 DZP >>> #Vova >>> C 3 0.00000 >>> n=2 0 2 E 39.65304 6.21693 >>> 7.40483 4.90026 >>> n=2 1 2 E 27.05294 3.74121 >>> 7.88345 3.11808 >>> n=3 2 1 E 55.60264 0.01540 >>> 3.93573 >>> %endblock PAO.Basis >>> >>> >>> >>> >>> >>> # 6.4 Lattice, coordinates, k-sampling >>> >>> LatticeConstant 8.96 Ang # 6.05 350Ry, 5.93845 Ang Exp, 5.936 Exp, >>> 5.84_LDA_Zhenya >>> >>> %block LatticeVectors >>> 1.0 0 0 #18A crystal + 12Avacuum >>> 0 1.0 0 >>> 0 0 1.4375 >>> %endblock LatticeVectors >>> >>> AtomicCoordinatesFormat Ang >>> AtomicCoorFormatOut Ang >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> %block AtomicCoordinatesAndAtomicSpecies >>> -0.03167 -0.11487 -0.35971 1 >>> -0.12412 -0.42211 2.92565 2 >>> 1.85899 2.43724 -0.06194 2 >>> 4.40361 4.31212 -0.38969 1 >>> 6.99200 6.23198 -0.88879 2 >>> 2.46456 6.94775 -0.15215 2 >>> 6.36927 1.84289 0.08180 2 >>> -0.09247 -0.14207 6.12437 1 >>> 2.57611 1.64461 5.69084 2 >>> 4.35503 4.31005 6.09334 1 >>> 6.18152 6.97008 6.46046 2 >>> 4.59235 4.49865 2.91059 2 >>> 4.43687 3.75124 9.32494 2 >>> 0.44143 -0.12135 9.34642 2 >>> 3.78065 0.42371 2.39084 3 >>> 4.82458 -0.31863 3.15069 4 >>> 3.28270 -0.20569 1.72441 5 >>> 4.20292 1.18515 1.82761 5 >>> 3.08493 0.84035 3.03696 5 >>> 5.25142 0.34763 3.90531 5 >>> 5.60253 -0.63714 2.45202 5 >>> 4.36520 -1.18663 3.63088 5 >>> 4.08008 0.15264 8.72657 3 >>> 4.82907 -0.48545 9.84708 4 >>> 4.39959 -0.21875 7.81266 5 >>> 4.21776 1.18640 8.72722 5 >>> 3.05391 -0.01415 8.80689 5 >>> 4.48385 -0.06168 10.79380 5 >>> 5.89626 -0.28577 9.71242 5 >>> 4.64461 -1.56270 9.82703 5 >>> -0.85527 5.05646 2.32772 3 >>> 0.08950 4.13502 3.02005 4 >>> -0.81071 4.97580 1.29648 5 >>> -0.65212 6.05774 2.55366 5 >>> -1.84958 4.87012 2.59300 5 >>> -0.01489 4.27318 4.09978 5 >>> 1.10925 4.37398 2.70535 5 >>> -0.15654 3.10553 2.74484 5 >>> 7.04591 2.46318 6.25281 2 >>> 1.72806 6.16802 6.24656 2 >>> -0.59017 4.78536 8.67712 3 >>> 0.30844 3.96725 9.53987 4 >>> -1.16287 4.17787 8.05170 5 >>> -0.03405 5.40998 8.05433 5 >>> -1.22474 5.36318 9.25668 5 >>> 0.88403 4.63525 10.18598 5 >>> 0.97946 3.39039 8.89784 5 >>> -0.30006 3.29480 10.15037 5 >>> %endblock AtomicCoordinatesAndAtomicSpecies >>> >>> >>> #%block GeometryConstraints >>> #position 1 2 >>> #%endblock GeometryConstraints >>> >>> #kgrid_cutoff 20 Ang >>> >>> #BandLinesScale pi/a >>> #BandLinesScale ReciprocalLatticeVectors >>> >>> #%block BandLines >>> #1 1 1 1 L >>> #20 0 0 0 G >>> #20 1.5 0 1.5 K >>> #10 2 0 0 X >>> #20 0 0 0 G >>> #%endblock Bandlines >>> >>> %block kgrid_Monkhorst_Pack >>> 8 0 0 0 >>> 0 8 0 0 >>> 0 0 8 0 >>> %endblock kgrid_Monkhorst_Pack >>> >>> >>> >>> >>> # 6.5 DFT, Grid, SCF >>> >>> XC.functional GGA >>> XC.authors PBE >>> #SpinPolarized true >>> MeshCutoff 375 Ry >>> FilterCutoff 375 Ry >>> MaxSCFIterations 199 # Maximum number of SCF iter >>> DM.MixingWeight 0.05 # New DM amount for next SCF cycle >>> DM.NumberPulay 10 >>> DM.PulayOnFile false >>> DM.NumberKick 50 >>> #DM.KickMixingWeight 0.1 >>> #DM.Tolerance 0.00001 # 0.0004 >>> #DM.EnergyTolerance 0.00005 eV >>> >>> >>> >>> >>> >>> #%block PolarizationGrids >>> # 7 3 3 yes >>> # 3 7 3 yes >>> # 3 3 7 yes >>> #%endblock PolarizationGrids >>> >>> >>> %block PolarizationGrids >>> 10 3 4 yes >>> 2 20 2 no >>> 4 4 15 >>> %endblock PolarizationGrids >>> >>> >>> >>> # 6.6 Eigenvalue problem: order-N or diagonalization >>> >>> SolutionMethod diagon >>> #Diag.DivideAndConquer false >>> #NumberOfEigenStates 10000 # total is ~27000 SZ >>> #OccupationFunction MP >>> #OccupationMPOrder 1 >>> #ElectronicTemperature 300 K >>> #ON.ChemicalPotentialUse true >>> >>> >>> >>> # 6.7 Molecular dynamics and relaxations >>> >>> MD.TypeOfRun CG >>> #MD.NoseMass 600 Ry*fs**2 >>> >>> MD.NumCGsteps 9950 >>> MD.MaxCGDispl 0.15 Ang >>> MD.MaxForceTol 0.040 eV/Ang >>> >>> #MD.LengthTimeStep 1 fs >>> #MD.FinalTimeStep 10000 >>> #MD.InitialTemperature 550 K >>> #MD.TargetTemperature 550 K >>> >>> >>> >>> >>> >>> >>> # 6.8 Parallel options >>> >>> #BlockSize 426 # for 16 procs #852 for 8 # DZP 6813 orbitals >>> #ProcessorY 8 >>> #Diag.Memory 4 >>> #Diag.ParallelOverK true >>> >>> >>> >>> # 6.9 Efficiency options >>> >>> # 6.10 Output options >>> >>> WriteMDXmol true >>> WriteCoorXmol true >>> WriteMDhistory true >>> WriteXML false >>> #WriteForces true >>> #WriteMullikenPop 1 >>> >>> >>> >>> >>> # 6.11 Options for saving/reading information >>> UseSaveData true >>> MD.UseSaveCG true >>> >>> #SaveRho true >>> #SaveDeltaRho true >>> #SaveElectrostaticPotential true >>> #SaveTotalPotential true >>> #SaveIonicCharge true >>> #SaveTotalCharge true >>> >>> %block LocalDensityOfStates >>> -7.15 12.00 eV >>> %endblock LocalDensityOfStates >>> >>> %block ProjectedDensityOfStates >>> -7.0 12.0 0.05 521 eV #min, max, broaden 100meV, steps every >>> 25meV >>> %endblock ProjectedDensityOfStates >>> >>> >>> #WriteDenchar true >>> >>> #%block WaveFuncKPoints >>> # 0.0 0.0 0.0 from 1040 to 1055 # traps # HOMO 1042 >>> #%endblock WaveFuncKpoints >>> >>> >>> #OpticalCalculation true >>> #Optical.EnergyMinimum 0 eV >>> #ptical.EnergyMaximum 4.5 eV >>> #Optical.Broaden 0.01 eV >>> #Optical.NumberOfBands 1100 # LUMO 1085 >>> >>> >> >> >> -- >> ----------------------------------------------------------- >> Pablo Aguado Puente >> [email protected] >> ------------------------------------------------------------ >> > > -- ----------------------------------------------------------- Pablo Aguado Puente [email protected] ------------------------------------------------------------
