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hello
I want to optimize the acell for LaCoO3 and my input variables are:

Crystalline LaCoO3(cubic) : optimization of the lattice parameter
# at fixed number of k points and broadening.

#Definition of occupation numbers
occopt 4
tsmear 0.05

#Definition of the unit cell
acell 3*7.22
rprim 1.0 0.0 0.0
0.0 1.0 0.0
0.0 0.0 1.0

#Optimization of the lattice parameters

optcell 2

ionmov 3
ntime 10
dilatmx 1.67
ecutsm 0.1

#Definition of the atom types
ntypat 3
znucl 57 27 8


#Definition of the atoms
natom 5
typat 1 2 3 3 3
xred
0.0 0.0 0.0
0.5 0.5 0.5
0.5 0.5 0.0
0.5 0.0 0.5
0.0 0.5 0.5
#Definition of the planewave basis set
ecut 80.0

#Exchange-correlation functional
ixc 1

#Definition of the k-point grid
kptopt 1
ngkpt 2 2 2
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 SCF procedure
nstep 65
toldfe 1.0d-6


and the output is:

*****************************************************************************************
acell 7.9796344683E+00 7.9796344683E+00 7.9796344683E+00 Bohr
******************************************************************************************
amu 1.38905500E+02 5.89332000E+01 1.59994000E+01
dilatmx 1.67000000E+00
ecut 8.00000000E+01 Hartree
ecutsm 1.00000000E-01 Hartree
etotal -8.5460495699E+01
fcart 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
ionmov 3
kpt -2.50000000E-01 5.00000000E-01 0.00000000E+00
-2.50000000E-01 -2.50000000E-01 2.50000000E-01
-2.50000000E-01 0.00000000E+00 0.00000000E+00
5.00000000E-01 5.00000000E-01 2.50000000E-01
kptrlen 2.50108137E+01
kptopt 1
kptrlatt 2 -2 2 -2 2 2 -2 -2 2
P mkmem 4
natom 5
nband 18
ngfft 100 100 100
nkpt 4
nstep 65
nsym 48
ntime 10
ntypat 3
occ 2.000000 2.000000 2.000000 2.000020 2.000823 2.001087
2.003521 2.022750 2.078934 2.085045 2.119327 2.102803
1.691270 1.445309 1.343083 1.276361 0.014275 0.000262
2.000000 2.000000 2.000000 2.000026 2.001194 2.001194
2.006711 2.011883 2.011883 2.140209 2.140209 2.058666
1.676373 1.567475 1.567475 0.147884 0.147884 0.001153
2.000000 2.000000 2.000000 2.000324 2.001960 2.001960
2.076777 2.076777 2.093798 2.110762 2.117024 2.113831
2.113831 1.901386 1.575779 1.575779 0.816844 0.000445
2.000000 2.000000 2.000000 2.000001 2.000441 2.000661
2.001520 2.004844 2.004844 2.098822 2.098822 1.784954
1.237877 1.214865 1.214865 0.078236 0.001528 0.003746
occopt 4
optcell 2
shiftk 5.00000000E-01 5.00000000E-01 5.00000000E-01
spgroup 221
strten 8.9648558286E-06 8.9648558892E-06 8.9648558684E-06
0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
symrel 1 0 0 0 1 0 0 0 1 -1 0 0 0 -1 0 0 0 -1
-1 0 0 0 1 0 0 0 -1 1 0 0 0 -1 0 0 0 1
-1 0 0 0 -1 0 0 0 1 1 0 0 0 1 0 0 0 -1
1 0 0 0 -1 0 0 0 -1 -1 0 0 0 1 0 0 0 1
0 1 0 1 0 0 0 0 1 0 -1 0 -1 0 0 0 0 -1
0 -1 0 1 0 0 0 0 -1 0 1 0 -1 0 0 0 0 1
0 -1 0 -1 0 0 0 0 1 0 1 0 1 0 0 0 0 -1
0 1 0 -1 0 0 0 0 -1 0 -1 0 1 0 0 0 0 1
0 0 1 1 0 0 0 1 0 0 0 -1 -1 0 0 0 -1 0
0 0 -1 1 0 0 0 -1 0 0 0 1 -1 0 0 0 1 0
0 0 -1 -1 0 0 0 1 0 0 0 1 1 0 0 0 -1 0
0 0 1 -1 0 0 0 -1 0 0 0 -1 1 0 0 0 1 0
1 0 0 0 0 1 0 1 0 -1 0 0 0 0 -1 0 -1 0
-1 0 0 0 0 1 0 -1 0 1 0 0 0 0 -1 0 1 0
-1 0 0 0 0 -1 0 1 0 1 0 0 0 0 1 0 -1 0
1 0 0 0 0 -1 0 -1 0 -1 0 0 0 0 1 0 1 0
0 1 0 0 0 1 1 0 0 0 -1 0 0 0 -1 -1 0 0
0 -1 0 0 0 1 -1 0 0 0 1 0 0 0 -1 1 0 0
0 -1 0 0 0 -1 1 0 0 0 1 0 0 0 1 -1 0 0
0 1 0 0 0 -1 -1 0 0 0 -1 0 0 0 1 1 0 0
0 0 1 0 1 0 1 0 0 0 0 -1 0 -1 0 -1 0 0
0 0 -1 0 1 0 -1 0 0 0 0 1 0 -1 0 1 0 0
0 0 -1 0 -1 0 1 0 0 0 0 1 0 1 0 -1 0 0
0 0 1 0 -1 0 -1 0 0 0 0 -1 0 1 0 1 0 0
toldfe 1.00000000E-06 Hartree
tsmear 5.00000000E-02 Hartree
typat 1 2 3 3 3
wtk 0.37500 0.25000 0.18750 0.18750
xangst 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
2.1113203556E+00 2.1113203556E+00 2.1113203556E+00
2.1113203556E+00 2.1113203556E+00 0.0000000000E+00
2.1113203556E+00 0.0000000000E+00 2.1113203556E+00
0.0000000000E+00 2.1113203556E+00 2.1113203556E+00
xcart 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
3.9898172341E+00 3.9898172341E+00 3.9898172341E+00
3.9898172341E+00 3.9898172341E+00 0.0000000000E+00
3.9898172341E+00 0.0000000000E+00 3.9898172341E+00
0.0000000000E+00 3.9898172341E+00 3.9898172341E+00
xred 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
5.0000000000E-01 5.0000000000E-01 5.0000000000E-01
5.0000000000E-01 5.0000000000E-01 0.0000000000E+00
5.0000000000E-01 0.0000000000E+00 5.0000000000E-01
0.0000000000E+00 5.0000000000E-01 5.0000000000E-01
znucl 57.00000 27.00000 8.00000



I think acell differs a lot !!!!!!
what must I do?

thanks

Some suggestions:

1) your ecut is really high, what pseudopotentials are you using? You could do this with PAW with an ecut of 15 or maybe less.

2) Your kpt set is very small, what is kptrlen in the output file? To get stresses accurately is not easy, you probably need a bigger kpt set (bigger ngkpt).

3) Your nshiftk and shiftk are appropriate for an FCC structure but I don't think are a good choice for a primitive cubic structure like this.

To solve 1, switch to PAW.

To solve 2 and 3, remove nshiftk and shiftk from your input, set prtkpt 1, and set kptrlen to 40. It will give you suggested kptrlatt that are suitable for your structure and that have kptrlen of 40, a good starting point for convergence studies. Then re-run with prtkpt 0 and kptrlatt at your new value. Do all this before you start optimizing anything.

Once you can compute the pressure (stress) of the input structure accurately, then start optimizing acell.

Also, what is the magnetic behavior of your sample? I bet it's not trivial but you are forcing it to be diamagnetic (nsppol 1 is the default and you haven't changed it in your input). If you haven't already done so, do the tutorials on spin.

Good luck!

Joe

One more think I forgot: when you run with prtkpt 1 and kptrlen 40, also remove ngkpt. Later when you add the kpt mesh back in, add it as kptrlatt only using the output from prtkpt 1.