  When electron doped, the layered transition metal nitrides ${\cal T}$NCl
(${\cal T}$ = group IVB transition metal ion) become impressive superconductors
with critical temperature T$_c$= 15-26K. Here we take the most studied member,
ZrNCl, as a representative and calculate the dielectric response
$\epsilon(\omega)$ versus frequency and concentration of doped electronic
carriers. The static dielectric constant $\epsilon_{\infty}$=5 is reproduced
extremely well. We establish that the differences between rigid band modeling
and virtual crystal treatment are small, and compare also with actual lithium
doping using supercells. We obtain the variations upon changing the doping
level of the reflectivity and energy loss function as well, many of which are
found not to be correlated with the observed (non)variation of T$_c(x)$. The
main plasmon peaks appear where the electron gas model suggests, in the range
1.2-2.0 eV for $x$ varying from 0.16 to 0.50.
