Noncollinear (NC) spin means that the spin can point in any direction in space, not just "up" and "down". So the NC spin representation is a matrix with more entries that just 2.

(1) if you do SCF with NC spin (e.g. NCGGA.PBE), the converged ground state will be in the noncollinear spin representation.

(2) Noncollinear transport just means that you allow for ground-state spins pointing in any direction what calculating the transmission spectrum.

(3) SOC requires NC representation, but you can do NC without the SOC.

(4) yes, SOC is enabled by choosing the appripriate combination of basis set and pseudopotential (I recommend SG15 for this), e.g.

`#----------------------------------------`

# Basis Set

#----------------------------------------

basis_set = [

BasisGGAPseudoDojoSO.Carbon_Medium,

]

#----------------------------------------

# Exchange-Correlation

#----------------------------------------

exchange_correlation = SOGGA.PBE