This directory contains some small tools for generation or manipulation of
POSCAR files. The available utilities are:


supercell:  Generates a large supercell out of a given small cell. The program
            reads a file POSOLD reflecting a valid POSCAR file and requests
            three new lattice vectors from standard input. The three vectors
            given must be INTEGER linear combinations ot the lattice vectors
            provided in POSOLD. The program generates a file POSNEW containing
            all atomic coordinates of the structure within the new unit cell.
            For example entering a primitive zinc-blende unit cell in POSOLD

             SiC bulk
                4.332
              0.5 0.5 0.0
              0.0 0.5 0.5
              0.5 0.0 0.5
                1  1
              Direct
              0.00 0.00 0.00
              0.25 0.25 0.25

            and providing

              5 0 0
              0 5 0
              0 0 5

            on standard input would create a simple cubic 1000-atom supercell.


redim:      Redimension a cell WITHOUT changing the absolute atomic coordinates.
            This tool also reads from POSOLD and writes to POSNEW and assumes
            three numbers on standard input for the redimensioning along each
            of the unit cell axis directions. You may either specify the new
            lattice vector length in absolute (Angstroem) units [positive value]
            or a relative scaling factor [negative value]. The purpose of this
            tool is to change the size of vacuum region of supercells containing
            a molecule, an infinite chain, or a surface slab structure keeping
            all atomic distances and bond angles. KNOWN BUGS: The coordinates
            are simply rescaled and no connectivity test / potential application
            of periodic boundary conditions is performed, i.e., check your input
            coordinates carefully! They need to cover a single interval, e.g.,
            "-0.1, 0.0, 0.1, 0.2" would work but not the (equivalent) sequence
            "0.9 0.0, 0.1, 0.2" since then the "0.9" would be separated off from
            the rest by rescaling (e.g. rescaling of the cell by a factor 2 what
            means rescaling the direct coordinates by a factor 1/2 would result
            in the useful sequence "-0.05, 0.0, 0.05, 0.1" in the first case but
            in the useless sequence "0.45, 0.0, 0.05, 0.1" in the latter case).


translate:  As the name says: translate the coordinates of a supercell. Also
            reads from POSOLD and writes to POSNEW and expects three shifts
            along each lattice vector directions on standard input. The main
            purpose is usually to shift a certain atom towards a certain special
            coordinate (e.g. 0 0 0) for easier analysis of the nearest-neighbour
            geometry, creation of vacancies or impurites at this points or to
            bring coordinates into a single interval (e.g. for use of redim).