For a number of reasons, it is useful to be able to convert the Kohn-Sham
orbitals generated by traditional plane-wave codes into a set of support
functions and a density-kernel which can be used as input in a linear-scaling
code. One such reason is the need for careful
density-matrix initialisation, discussed in section 8.3.
For analysis it is also useful to be able to perform the reverse operation of
extracting the Kohn-Sham orbitals and occupation numbers from the
density-matrix. In this chapter we describe methods for performing both of
these operations.