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USING CERIUS2 (CASTEP) TO GENERATE INPUT FOR A VASP JOB

To run a VASP job, you will need the following files:
INCAR - parameters that define the job to be run
POSCAR - the positions of the ions and the unit cell vectors
POTCAR - the pseudopotential - get from /home/steckel/vasp_pseudopots on indigo5-8 
KPOINTS - the mesh that determines the choice of the kpoints 

All of these files are described in the VASP guide.

The Cerius2 interface can be used both to generate the (fractional)
coordinates for the positions of the ions as well as to get an idea
of the "default" values that Cerius2 picks for things like kpoints, 
cutoff, ect. (This can be helpful for comparison...)  From the 
Cerius2/CASTEP file "name.geom" you can directly obtain the lattice
vectors and the direct (fractional) coordinates to use in the POSCAR. 

Here is a sample INCAR file (for a geometry optimization):

SYSTEM =  c(4x2)

Electronic Relaxation 1
PREC  = med

Geom opt
NSW  = 50     !the number of ionic steps
ISF  = 2      !calc stress tensor, don't change cell
IBRION = 1

DOS related values:
ISMEAR =     0;   SIGMA  =    0.00

The cut-off is not specified directly but precision=medium is chosen.  
The energy cutoff of the plane-wave basis set will be determined by the
program according to the parameters found in the POTCAR files; this is
described in the VASP guide. 

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USING SPARTAN TO VIEW STRUCTURES FROM VASP:

To convert a CONTCAR or POSCAR file to something Spartan can import,
I wrote an (unsophisticated!) fortran90 program called 
mkspartan.f90.  It needs to be compiled
for each type of unit cell; i.e. the number of atoms is hard coded in. 
Sorry, but I could not figure out how to allocate the arrays dynamically
and also use modules.

In addition, one must write a file called "batting_order" which lists
the atomic masses for your unit cell.  For example, a model of SiH4
would have a "batting_order" file that looks like this:
14
1
1
1
1 

The mkspartan program reads the filenames for the POSCAR files and the
names you want it to assign for the Spartan input from a file called
filenames that has the following form:
   CONTCAR_ma    spar.ma
   CONTCAR_mb    spar.mb
   CONTCAR_mc    spar.mc
   CONTCAR_md    spar.md

If you would like to import the structure to Cerius2/CASTEP, you can 
export the structure from Spartan as a .pdb file, which can be loaded
by Cerius2.  
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GENERATING INPUT FOR THE NUDGED ELASTIC BAND

The NEB algorithm is implemented in VASP but you will need vasp compiled
on a parallel computer (or cluster) in order to run NEB jobs.   Only the
serial version of VASP is available on indigo 5-8 or power1-3. 

To run a NEB job, please first read the VASP guide to understand how the 
input is organized.  I wrote another (unsophisticated!) fortran90 
program called mkimages.f90 that takes two POSCAR or CONTCAR files
and interpolates between the two geometries to generate a number
of "images".  This also must be compiled specifically for the number
of atoms in the unit cell. 

Be warned; your images will be messed up if you do not have consistent
ordering of atoms in your reactant and product POSCAR files.  :)

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