  A previously proposed computational procedure for constructing a set of
nonorthogonal strongly localised one-electron molecular orbitals (O. Danyliv,
L. Kantorovich - physics/0401107) is applied to a perfect $\alpha$-quartz
crystal characterised by an intermediate type of chemical bonding. The orbitals
are constructed by applying various localisation methods to canonical
Hartree-Fock orbitals calculated for a succession of finite molecular clusters
of increased size with appropriate boundary conditions. The calculated orbitals
span the same occupied Fock space as the canonical HF solutions, but have an
advantage of reflecting the true chemical nature of the bonding in the system.
The applicability of several localisation techniques as well as of a number of
possible choices of localisation regions (structure elements) are discussed for
this system in detail.
