  The quasi-independent curvilinear coordinate approximation (QUICCA) method
[K. N\'emeth and M. Challacombe, J. Chem. Phys. {\bf 121}, 2877, (2004)] is
extended to the optimization of crystal structures. We demonstrate that QUICCA
is valid under periodic boundary conditions, enabling simultaneous relaxation
of the lattice and atomic coordinates, as illustrated by tight optimization of
polyethylene, hexagonal boron-nitride, a (10,0) carbon-nanotube, hexagonal ice,
quartz and sulfur at the $\Gamma$-point RPBE/STO-3G level of theory.
