Dear all
I want to perform a vc-relax calculation for NbSi2 :
First i use the following input :
?&CONTROLtitle = 'NbSi2',calculation = 'vc-relax',nstep = 100,etot_conv_thr =
1.d-7,forc_conv_thr = 1.d-5,
tstress = .true.,
prefix = 'NbSi2',
verbosity = 'high',
disk_io = 'low',
tprnfor = .true.,
/
&SYSTEM
celldm(1) = 1.d0,
ibrav = 0,
nat = 9,
ntyp = 2,
ecutwfc = 30.d0,
ecutrho = 300.d0,
nspin = 1,
occupations = 'smearing',degauss = 0.005d0,
/
&ELECTRONS
conv_thr = 1.d-7,
mixing_beta = 0.1d0,
diagonalization = 'cg',
/
&IONS
ion_dynamics = 'bfgs',
bfgs_ndim = 1,
/
&CELL
cell_dynamics = 'bfgs',
press = 0.d0,
press_conv_thr = 0.200d0,
cell_dofree = 'xyz',
/
ATOMIC_SPECIES
Si 28.0855d0 Si.pbe-n-van.UPF
Nb 92.90638d0 Nb.pbe-nsp-van.UPF
K_POINTS automatic
6 6 1 0 0 0
ATOMIC_POSITIONS crystal
Nb 0.50000 0.00000 0.00000
Si 0.16578 0.33156 0.00000
Nb 0.00000 0.50000 0.66667
Si 0.66844 0.83422 0.66667
Nb 0.50000 0.50000 0.33333
Si 0.16578 0.83422 0.33333
Si 0.83422 0.66844 0.00000
Si 0.33156 0.16578 0.66667
Si 0.83422 0.16578 0.33333
CELL_PARAMETERS
9.053677211 0.000000000 0.000000000
0.000000000 9.053677211 0.000000000
0.000000000 0.000000000 12.449514813
During convergence, the error was : Not enough space allocated for radial FFT:
try restarting with a larger cell_factor
So, i use a cell_factor = 2 , then the structure was converged, but the cell
parameters of the relaxed structure differs so much from the cell-parameters of
the begining.
relaxed cell parameters :10.94171211 0.000000000 0.0000000000.000000000
10.94171211 0.0000000000.000000000 0.000000000 9.245414256
I try to decrease ecutwfc for 25 Ry and ecutrho = 200 Ry, and to change the
'smearing' , but always i converge the structure with a big difference between
cell_parameters.the difference between cell-parameters is about 20%.
So my question is : What is the real problem in my input ?
Thanks a lot for your helping
best regards
Ali ALLAMPhysics of materials - 2nd year PhDAix-Marseille UniversityMarseille
13013FRANCE
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