A total of 2554 G-vectors was originally chosen [8] for the number
of 
's used in
the expansion of in the germanium solid.
Obviously, this is too large a number for any kind of
optimisation procedure and so the first simplification is to reduce
the number of free parameters by forcing all the components of a star of
's to take the same value. A star of 
's is a group
of 
's related by the point group symmetry of the lattice.
This allows (
) to be written as.
This reduces the number of free parameters to around 130.
This is still a very large space in which to perform an accurate
optimisation so it was decided to investigate the effect of reducing the
number of stars in the expansion of ¸, as it was suspected that the
higher order stars contained only noise. Once the minimum number of
stars used to describe had been established, then this number
could be used in an optimisation procedure.
