Create supercells

Before starting, it is recommended to check health condition of your POSCAR like as follows (fropho is assumed in $PATH),
	% echo 'find_symmetry'|fropho
If your cell doesn't have enough symmetry which you intend, you need to modify your crystal shape. In such a case, the cleanCrystal.rb script may help you. Be sure that the fropho symmetry finder often fails. Sometimes you may find smaller unit cells or primitive cells in your POSCAR. The axes of these cells are automatically determined and often be strange. If you have no trouble, start phonon analysis !

First you need a working directory. In this directory, you must prepare POSCAR (VASP style position file) file. At the present time, the file name must be ``POSCAR''. The fropho setting file ``INPHON'' is prepared. The file name is whatever as you like. Supercell is required to calculated force constants in real space. The supercell must be enough large until all the force constants become enough small. If you want to create $ 2 \times 2 \times 2$ supercell, write to INPHON like this,

	NDIM = 2 2 2
Here, the ``_'' is a space which must be inserted to input file. Then type,
	% fropho < INPHON
You have supercell position file (SPOSCAR) and displacements file (DISP). SPOSCAR file also follows the VASP POSCAR format. DISP file contains minimum number of the displacements determined by symmetry of crystal. By using DISP and SPOSCAR files, you may create position files which contain displacements.

togo 2009-02-12
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