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Hi abinit user,
I am working on structural optimization . but every time I am getting boxcut error. even though I am reducing ecut is not working for me. Please help. here is the content of input file.
#Define the methodology to find the minimum
ionmov 2 # Use the modified Broyden algorithm
ntime 150 # Maximum number of Broyden "timesteps"
tolmxf 5.0d-4 # Stopping criterion for the geometry optimization : when
# the residual forces are less than tolmxf, the Broyden
# algorithm can stop


toldff 5.0d-5 # Will stop the SCF cycle when, twice in a row,


optcell 2


#Definition of the unit cell
acell 12.237 8.255 8.508 angstrom



#rprim 1 0 0 0 1 0 0 0 1 # This line, defining orthogonal primitive vectors,
# is commented, because it is precisely the default value of rprim

#Definition of the atom types


#Definition of the atoms
natom 78

#Definition of the k-point grid
kptopt 1 # Enter the k points manually
ngkpt 2 4 4 # Only one k point is needed for isolated system,
# taken by default to be 0.0 0.0 0.0
shiftk 0.5 0.5 0.5

#Definition of the SCF procedure

nstep 100 # Maximal number of SCF cycles
#toldfe 1.0d-6 # Will stop when, twice in a row, the difference
# between two consecutive evaluations of total energy
# differ by less than toldfe (in Hartree)
# This value is way too large for most realistic studies of materials
diemac 2.0 # Although this is not mandatory, it is worth to
# precondition the SCF cycle. The model dielectric
# function used as the standard preconditioner
# is described in the "dielng" input variable section.
dilatmx 0.925

# Here, we follow the prescriptions for molecules
# in a big box

#Definition of the planewave basis set
ecut 500 eV
ecutsm 1 Hartree

# add to conserve old < 6.7.2 behavior for calculating forces at each SCF step
optforces 1

and here is the error which I am getting:

ERROR
src_file: getcut.F90
src_line: 157
mpi_rank: 0
message: |
Choice of acell, ngfft, and ecut
===> basis sphere extends BEYOND fft box !
Recall that boxcut=Gcut(box)/Gcut(sphere) must be > 1.
Action : try larger ngfft or smaller ecut.
Note that ecut=effcut/boxcut**2 and effcut= 0.517851

Dear Mustafa,
I would advise you to use ecutsm = 0.5 and 1.1>dilatmx>1.0 (you start with dilatmx=1.02 for example).
Let us know if this improves your boxcut problem,
Best wises,
Eric

Dear Eric,
Thank you for your help. I used it and this improve my boxcut problem.
Regards,
mustafa

Dear Eric,

I tried several times by change of dilatmx but always it displays this error message:


Difference of energy with previous step (new-old):
Absolute (Ha)=-4.72926E-01
Relative =-9.83569E-04
fconv : at Broyd/MD step 8, gradients have not converged yet.
max grad (force/stress) = 1.8840E-01 > tolmxf= 5.0000E-04 ha/bohr (free atoms)

Geometry Optimization Precondition: 0

--- !WARNING
src_file: mover.F90
src_line: 834
message: |
The new primitive vectors rprimd (an evolving quantity)
are too large with respect to the old rprimd and the accompanying dilatmx: 1.043683E+00
This large change of unit cell parameters is not allowed by the present value of dilatmx.
An adequate value would have been dilatmx_new= 1.045934E+00
Calculation continues with limited jump, by rescaling the projected move by the factor 8.558994E-01.

Best regards
mustafa