test example of SiC optimization

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Hi,

When I tried to run the example "Optimizing a unit cell and geometry for Silicon-Carbide", first I got an error message to complain the lack of memory. After I increased it, the optimization converged, and got the following information


Lattice Parameters
     ------------------ 

     lattice vectors in a.u. (scale by  1.000000000 to convert to a.u.)

     a1=<   8.646  -0.000   0.000 >
a2=< -0.000 8.645 -0.000 >
a3=< -0.000 0.000 8.127 >
a= 8.646 b= 8.645 c= 8.127
alpha= 90.000 beta= 90.000 gamma= 90.000
omega= 607.4

My question is why the norm of a3 is not the same as the norm of a1. How can I force the optimization to keep the ratios between the norms of a1, a2, and a3 constant? In other words, I would like to optimization process to scale a1, a2, a3 by the same factor.

Other questions:

1. Where can I find all possible options for different directives?
  "set includelattice .true." only apprars in an example input file, but not in the section of "http://www.nwchem-sw.org/index.php/Release61:Top-level#SET"
other examples: set nwpw:stress_numerical .true. #currently only numerical stresses
set nwpw:psi_nolattice .true. # turns of unit cell checking for wavefunctions

Is there any list to tell users that those parameter can be set by "set nwpw:$$" for nwpw?


2. Where can I find the refence for "task band"? I can't find any relevant reference from documentation or the paper "NWChem: A comprehensive and scalable open-source solution for large scale molecular simulations"

3. I have used LAMMPS package. The documentation of LAMMPS is pretty easy to follow. Would you mind to take a look and revise the documentation which can include references and default settings?

Thank you in advance.

Dongsheng
Edited On 2:31:02 PM PDT - Thu, May 2nd 2013 by Zhdsheng

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http://www.nwchem-sw.org/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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