The number of spins to be used can be set with the variable number_of_spins:
number_of_spins 1
(for non-spin polarized LDA)
or
number_of_spins 2
(for spin-polarized LSDA)
Default: number_of_spins 1
To get a spin-polarized starting configuration for the self-consistent charge, use the spin polarization factors where you input the crystal structure.