  Using molecular dynamics simulation, we study dipolar glass in crystals
composed of slightly spheroidal, polar particles and spherical, apolar
impurities between metal walls. We present physical pictures of ferroelectric
glass, which have been observed in relaxors, mixed crystals (such as
KCN$_x$KBr$_{1-x}$), and polymers. Our systems undergo a diffuse transition in
a wide temperature range, where we visualize polar nanoregions (PNRs)
surrounded by impurities. In our simulation, the impurities form clusters and
their space distribution is heterogeneous. The polarization fluctuations are
enhanced at relatively high $T$ depending on the size of the dipole moment.
They then form frozen PNRs as $T$ is further lowered into the nonergodic
regime. As a result, the dielectric permittivity exhibits the characteristic
features of relaxor ferroelectrics. We also examine nonlinear response to
cyclic applied electric field and nonergodic response to cyclic temperature
changes (ZFC$/$FC), where the polarization and the strain change collectively
and heterogeneously. We also study antiferroelectric glass arising from
molecular shape asymmetry. We use an Ewald scheme of calculating the dipolar
interaction in applied electric field.
