Hi everybody

I am trying to calculate elastic properties of CsPbBr3, I do relaxation to the cell using the following input:

ndtset 2 # There are 2 datasets in this calculation

# Set 1 : Internal coordinate optimization

ionmov1 2 # Use BFGS algorithm for structural optimization

ntime1 15 # Maximum number of optimization steps

tolmxf1 1.0e-6 # Optimization is converged when maximum force

# (Hartree/Bohr) is less than this maximum

#natfix1 3 # Fix the position of two symmetry-equivalent atoms

# in doing the structural optimization

#iatfix1 1 2 3

#iatfixx 3

#iatfixy 3

#iatfixz 3

# Set 2 : Lattice parameter relaxation (including re-optimization of

# internal coordinates)

dilatmx2 1.05 # Maximum scaling allowed for lattice parameters

getxred2 -1 # Start with relaxed coordinates from dataset 1

getwfk2 -1 # Start with wave functions from dataset 1

ionmov2 2 # Use BFGS algorithm

ntime2 30 # Maximum number of optimization steps

optcell2 2 # Fully optimize unit cell geometry, keeping symmetry

tolmxf2 1.0e-6 # Convergence limit for forces as above

strfact2 100

#natfix2 3

#iatfix2 1 2 3

#iatfixx2 3

#iatfixy2 3

#iatfixz2 3

#Common input data

#Starting approximation for the unit cell

acell 3*6.017 Angstr

rprim 0.0 0 1

1 0.0 0

0 1 0

#Definition of the atom types and atoms

ntypat 3

znucl 55 82 35

natom 5

typat 1 2 3 3 3

#Starting approximation for atomic positions in REDUCED coordinates

#based on ideal tetrahedral bond angles

xcart 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00

5.6852410708E+00 5.6852410708E+00 5.6852410708E+00

5.6852410708E+00 0.0000000000E+00 5.6852410708E+00

5.6852410708E+00 5.6852410708E+00 0.0000000000E+00

0.0000000000E+00 5.6852410708E+00 5.6852410708E+00

#Gives the number of bands, explicitely (do not take the default)

nband 23

#Definition of the plane wave basis set

ecut 38

ecutsm 0.5

pawecutdg 40

#Definition of the k-point grid

ngkpt 6 6 6

nshiftk 4

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

#Definition of the self-consistency procedure

diemac 10.0 # Model dielectric preconditioner

nstep 50 # Maxiumum number of SCF iterations

tolvrs 1.0d-18 # Strict tolerance on (squared) residual of the

# SCF potential needed for accurate forces and

# stresses in the structural optimization, and

# accurate wave functions in the RF calculations

# enforce calculation of forces at each SCF step

optforces 1

then I calculate ddk eigen values using the following input:

ndtset 3

# Set 1 : Initial self-consistent run

kptopt1 1

tolvrs1 1.0d-18 #need excellent convergence of GS quantities for RF runs

prtcif1 1

# Set 2 : Calculate the ddk wf's - needed for piezoelectric tensor and

# Born effective charges in dataset 3

getwfk2 -1

iscf2 -3 #this option is needed for ddk

kptopt2 2 #use time-reversal symmetry only for k points

nqpt2 1 #one wave vector will be specified

qpt2 0 0 0 #need to specify gamma point

rfelfd2 2 #set for ddk wf's only

rfdir2 1 1 1 #full set of directions needed

tolwfr2 1.0d-20 #only wf convergence can be monitored here

# Set 3 : response-function calculations for all needed perturbations

getddk3 -1

getwfk3 -2

kptopt3 2 #use time-reversal symmetry only for k points

nqpt3 1

qpt3 0 0 0

rfphon3 1 #do atomic displacement perturbation

rfatpol3 1 5 #do for all atoms

rfstrs3 3 #do strain perturbation

rfdir3 1 1 1 #the full set of directions is needed

tolvrs3 1.0d-10 #need reasonable convergence of 1st-order quantities

#Common input data

# acell COPY RELAXED RESULT FROM PREVIOUS CALCULATION

acell 3*6.0047171678 Angstr

rprim 0.0000000000E+00 0.0000000000E+00 1.0000000000E+00

1.0000000000E+00 0.0000000000E+00 0.0000000000E+00

0.0000000000E+00 1.0000000000E+00 0.0000000000E+00

#Definition of the atom types and atoms

ntypat 3

znucl 55 82 35

natom 5

typat 1 2 3 3 3

#Starting approximation for atomic positions in REDUCED coordinates

#based on ideal tetrahedral bond angles

# xred COPY RELAXED RESULT FROM PREVIOUS CALCULATION

# Here is a set of default values, for automatic testing : suppress it and fill the previous line

xcart 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00

5.6736350428E+00 5.6736350428E+00 5.6736350428E+00

5.6736350428E+00 0.0000000000E+00 5.6736350428E+00

5.6736350428E+00 5.6736350428E+00 0.0000000000E+00

0.0000000000E+00 5.6736350428E+00 5.6736350428E+00

#Gives the number of bands, explicitely (do not take the default)

nband 23 # For an insulator (if described correctly as an

# insulator by DFT), conduction bands should not

# be included in response-function calculations

#Definition of the plane wave basis set

ecut 38.0 # Maximum kinetic energy cutoff (Hartree)

ecutsm 0.5 # Smoothing energy needed for lattice paramete

# optimization. This will be retained for

# consistency throughout.

#Definition of the k-point grid

kptopt 1 # Use symmetry and treat only inequivalent points

ngkpt 6 6 6 # 4x4x4 Monkhorst-Pack grid

nshiftk 4

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

#Definition of the self-consistency procedure

diemac 10.0 # Model dielectric preconditioner

nstep 50 # Maxiumum number of SCF iterations

# enforce calculation of forces at each SCF step

optforces 1

The results are not correct and it tells me gamma point is not relaxed.

Any idea please?

Thnaks

Nawzad