A DC block is a capacitor with an infinite capacitance. During DC simulation the DC block is an open circuit. Thus, its MNA entries are all zero.
The MNA matrix entries of a DC block correspond to an ideal short circuit during AC analysis which is modeled by a voltage source with zero voltage.
The scattering parameters writes as follows.
A DC block is noise free. A model for transient simulation does not exist. It is common practice to model it as a capacitor with finite capacitance whose value is entered by the user.