Purpose

FilePot is a potential that computes things by writing atomic config to a file, running a command, and reading its output

it takes an argument string on initialization with one mandatory parameter

and two optional parameters

which defaults to pos, and

which default to zero. If min_cutoff is non zero and the cell is narrower than $2*min_cutoff$ in any direction then it will be replicated before being written to the file. The forces are taken from the primitive cell and the energy is reduced by a factor of the number of repeated copies.

The command takes 2 arguments, the names of the input and the output files. command output is in extended xyz form.

energy and virial (both optional) are passed via the comment, labeled as energy=E and virial="vxx vxy vxz vyx vyy vyz vzx vzy vzz".

per atoms data is at least atomic type and optionally a local energy (labeled local_e:R:1) and forces (labeled force:R:3)

right now (14/2/2008) the atoms_xyz reader requires the 1st 3 columns after the atomic type to be the position.

If you ask for some quantity from FilePot_Calc and it's not in the output file, it returns an error status or crashes (if err isn't present).