# Finite difference calculation of the Born effective charges of AlP
# The calculation proceeds by computing the change in cell polarization
# by a Berrys phase formula, due to moving one of the atoms in the cell
# Berry phase calculation of the polarization
# berryopt -1 triggers the implementation of M. Viethen
berryopt -1
rfdir 1 1 1
#Definition of the unit cell
# these cell parameters were derived from a relaxation run done with the
# current ecut and kpt values. The current ecut value used is very low but
# is done to speed the calculations.
#
# Note that for a cubic space group as found here, the primitive unit
# cell is often represented as (0,a/2,a/2); (a/2,0,a/2); (a/2,a/2,0).
# Here abinit uses 1/sqrt(2) as the normalizer and adjusts acell (the cell
# length scale) accordingly. All this is copied from the output of the relaxation
# run.
acell 7.2728565836E+00 7.2728565836E+00 7.2728565836E+00 Bohr
rprim 0.0000000000E+00 7.0710678119E-01 7.0710678119E-01
7.0710678119E-01 0.0000000000E+00 7.0710678119E-01
7.0710678119E-01 7.0710678119E-01 0.0000000000E+00
#Definition of the atom types and pseudopotentials
ntypat 2 # two types of atoms
znucl 15 13 # the atom types are Phosphorous and Aluminum
# the following norm-conserving pseudopotentials are stored in the abinit distribution, but are freely
# available through www.pseudo-dojo.org
# this set uses the Perdew-Wang parameterization of LDA for the xc model
pp_dirpath "$ABI_PSPDIR"
pseudos "Pseudodojo_nc_sr_04_pw_standard_psp8/P.psp8, Pseudodojo_nc_sr_04_pw_standard_psp8/Al.psp8"
#Definition of the atoms
natom 2 # two atoms in the cell
typat 1 2 # type 1 is Phosphorous, type 2 is Aluminum (order defined by znucl above and pseudos list)
nband 4 # nband is restricted here to the number of filled bands only, no empty bands. The theory of
# the Berrys phase polarization formula assumes filled bands only. Our pseudopotential choice
# includes 5 valence electrons on P, 3 on Al, for 8 total in the primitive unit cell, hence
# 4 filled bands.
#atomic positions. Here we do three separate computations, where the Al atom is moved (manually)
#from its equilibrium position at 0,0,0 in calculation 1, to (+/-0.01,0,0) offsets in calculations
#2 and 3. The P position is again taken from the value in the relaxation calculation done
#previously.
ndtset 3
jdtset 1 2 3
xcart1 2.5713431044E+00 2.5713431044E+00 2.5713431044E+00
0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
xcart2 2.5713431044E+00 2.5713431044E+00 2.5713431044E+00
1.0000000000E-02 0.0000000000E+00 0.0000000000E+00
xcart3 2.5713431044E+00 2.5713431044E+00 2.5713431044E+00
-1.0000000000E-02 0.0000000000E+00 0.0000000000E+00
#Numerical parameters of the calculation : planewave basis set and k point grid
ecut 5 # this value is very low but is used here to achieve very low calculation times.
# in a production environment this should be checked carefully for convergence and
# a more reasonable value is probably around 20
ecutsm 0.5
dilatmx 1.05
ngkpt 6 6 6
nshiftk 4 # this Monkhorst-Pack shift pattern is used so that the symmetry of the shifted grid
# is correct. A gamma-centered grid would also have the correct symmetry but would be
# less efficient.
shiftk 0.5 0.5 0.5
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
#Parameters for the SCF procedure
toldfe 1.0d-15
nstep 8
# suppress printing of density, wavefunctions, etc for this tutorial
prtwf 0
prtden 0
prteig 0
##############################################################
# This section is used only for regression testing of ABINIT #
##############################################################
#%%
#%% [setup]
#%% executable = abinit
#%% [files]
#%% files_to_test =
#%% tffield_1.abo, tolnlines= 10, tolabs= 1.100e-08, tolrel= 3.000e-04
#%% [paral_info]
#%% max_nprocs = 2
#%% [extra_info]
#%% authors = J. Zwanziger, M. Veithen
#%% keywords = NC, DFPT
#%% description =
#%% Finite difference calculation of the Born effective charges of AlP
#%%