We study numerically the relaxation and the pinning gap of a 2D electr
on crystal in the presence of randomly distributed distant dopants. Ou
r results agree with experiments and with analytic calculations based
on a perturbation in the deviations of the particle positions deltar/a
from the lattice positions. For parameters corresponding to the recen
t experimental studies (d/a congruent-to 3), the relaxation is dominat
ed by the longitudinal mode.