http://nwchemgit.github.io/index.php/Release61:Plane-Wave_Density_Functional_Theory#Unit_Cel...
The following input seems to work for me for SiC
title "SiC 8 atom cubic cell - geometry and unit cell optimization"
echo
permanent_dir ./perm
scratch_dir ./perm
start diamond
memory 950 mb
- Enter the geometry using fractional coordinates ****
geometry center noautosym noautoz print
system crystal
lat_a 4.00d0
lat_b 4.00d0
lat_c 4.00d0
alpha 90.0d0
beta 90.0d0
gamma 90.0d0
end
Si -0.50000d0 -0.50000d0 -0.50000d0
Si 0.00000d0 0.00000d0 -0.50000d0
Si 0.00000d0 -0.50000d0 0.00000d0
Si -0.50000d0 0.00000d0 0.00000d0
C -0.25000d0 -0.25000d0 -0.25000d0
C 0.25000d0 0.25000d0 -0.25000d0
C 0.25000d0 -0.25000d0 0.25000d0
C -0.25000d0 0.25000d0 0.25000d0
end
set nwpw:kbpp_ray .true.
set nwpw:kbpp_filter .true.
nwpw
ewald_rcut 3.0
ewald_ncut 8 #The default value of 1 needs to be increased for small cells
lmbfgs
xc pbe96
end
driver
clear
maxiter 40
end
set nwpw:cif_filename sic.opt # create a CIF file containing optimization history
set includestress .true. # this option tells driver to optimize the unit cell
task pspw optimize ignore
nwpw
monkhorst-pack 2 2 2
end
task band optimize ignore
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