Optimization of unit cell leads to lat_c parameter that is 3 ang smaller than expt.
expt: a= 5.071 b= 5.071 c= 16.825
opt: a= 5.062 b= 5.062 c= 13.529
I have obtained similar results using:
ngrid 32 32 128
ngrid 32 32 96
nrid: 48 48 96
How can I improve the accuracy of my calculation?
My input deck follows:
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title "NaNO3 testing - using R-3c symmetry"
echo
start NaNO3
memory 4000 mb
permanent_dir ./perm
scratch_dir ./scratch
geometry
system crystal
lat_a 5.071
lat_b 5.071
lat_c 16.825
alpha 90.0
beta 90.0
gamma 120.0
end
symmetry R-3c
Na 0.00000 0.00000 0.00000
N 0.00000 0.00000 0.25000
O 0.2448 0.00000 0.25000
end
pspw
SIMULATION_CELL
ngrid 32 32 128
END
ewald_rcut 3.0
ewald_ncut 8
energy_cutoff 56.0
end
driver
clear
maxiter 51
end
set nwpw:cif_filename NaNO3
set includestress .true. # tell driver to optimize unit cell
set nwpw:zero_forces .true. # zeros the forces on the atoms
task pspw optimize
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