  A novel Genetic Algorithm is described that is suitable for determining the
global minimum energy configurations of crystal structures and which can also
be used as a polymorph search technique. This algorithm requires no prior
assumptions about unit cell size, shape or symmetry, nor about the ionic
configuration within the unit cell. This therefore enables true ab initio
crystal structure and polymorph prediction. Our new algorithm uses a real-space
representation of the population members, and makes use of a novel periodic cut
for the crossover operation. Results on large Lennard-Jones systems with FCC-
and HCP-commensurate cells show robust convergence to the bulk structure from a
random initial assignment and an ability to successfully discriminate between
competing low enthalpy configurations. Results from an ab initio carbon
polymorph search show the spontaneous emergence of both Lonsdaleite and
graphite like structures.
