# File for determining d/dk for LiNbO2 # # LiNbO2 should belongs to space group P63/mmc, group # number 194. # # Unit cell is hexagonal, with # a = 2.90 Angstroms # c = 10.46 Angstroms # # According to paper by Gerd Meyer and Rudolf Hoppe, we have # Li at 2a # Nb at 2d z = 0.25 # O at 4f z = 0.1263 # Relaxation of atomic positions has led to # z = 1/8 for the oxygens. # # We will need three datasets, one to calculate the # self-consistent wave function, and the second to calculate # the actual d/dk values. The third will calculate # the electric field perturbation and the born effective # charges. ndtset 3 #common options getwfk 1 # 1st dataset generates grounstate wfk and den getddk 2 kptopt 2 nqpt 1 qpt 0.0 0.0 0.0 ############################################################### # Dataset 1 - Self-consistent ground state ############################################################### tolvrs1 1.0e-18 # We want the potential to be really # well converged. iscf1 5 # Do calculation self-consistently, with # conjugate gradient mixing kptopt1 1 # Use symmetries getwfk1 0 getddk1 0 nqpt1 0 prtwf1 1 # Output the wavefunction prtden1 1 # Output the self-consistent density ############################################################### # Dataset 2 - d/dk of wavefunction ############################################################### rfelfd2 2 # Tell abinit to actually to the d/dk calculation. rfdir2 1 1 1 # Do all three directions (maybe we only have to # do a and c directions? I dunno.) getddk2 0 # We're generating d/dk's here, so don't need to load them tolwfr2 1.0e-22 # Strict tolerance on convergence of the # wave function, since these results will # be used in later calculations. iscf2 -3 # Non-selfconsistent calculation for d/dk ############################################################### # Dataset 3 - electric field and atomic displacements ############################################################### rfphon3 1 # This will tell abinit to calculate response # to phonons (ie. atomic displacements) rfatpol3 1 8 # This would displace all the atoms rfelfd3 3 # Perform electric field calculation rfdir3 1 1 1 # Set the directions iscf3 5 # Self consistent calculation. tolvrs3 1.0e-10 # Sorta strict tolerance on the residual potential ############################################################### # Common parameters ############################################################### #Definition of the unit cell acell 5.3808585426 5.3808585426 19.262436687 # Lengths of the primitive vectors (in Bohr) angdeg 90 90 120 # Specify angle between primitive translations #Definition of the atom types ntypat 3 # Three types of atoms, Li, Nb, O znucl 3 41 8 # We have 3-Li, 41-Nb, 8-O #Definition of the atoms natom 8 # I am treating the unit cell as containing # Li2Nb2O4. This will make it much simpler when # going to H(0.5) LiNbO2 typat 1 1 2 2 3 3 3 3 # First two atoms are Li, Second two are Nb, # Last four are O. xred # I will give the atomic coordinates in reduced c # coordinates. 0 0 0 0 0 1/2 1/3 2/3 3/4 2/3 1/3 1/4 1/3 2/3 0.121126 2/3 1/3 -0.121126 2/3 1/3 0.621126 1/3 2/3 0.378874 #Definition of the planewave basis set ecut 60.0 # We seem to have convergence here. #Definition of the k-point grid ngkpt 10 10 4 # We seem to have convergence here. nshiftk 1 # number of k-point shifts. This is recommended from # the abinit documentation for hexagonal symmetry shiftk 0.0 0.0 0.5 occopt 1 # There was some messages about metallic character # so we will treat this as a metallic substance # for this calculation. #tsmear 0.005 # Set the temperature for F-D distribution to 315K #output eigenvalues in ev. enunit 1 #Definition of the SCF procedure nstep 2000 # Maximal number cycles nband 18 # number of bands=#occupied bands nbdbuf 0 # zero bands as buffer diemac 10.0 # Although this is not mandatory, it is worth to # precondition the SCF cycle. The model dielectric #diemix 0.5 # function used as the standard preconditioner # is described in the "dielng" input variable section. # Here, we follow the prescriptions for molecules # in a big box