  It has been suggested recently, based on subtle field-theoretical
considerations, that the electromagnetic response of Weyl semimetals and the
closely related Weyl insulators can be characterized by an axion term E.B with
space and time dependent axion angle. Here we construct a minimal lattice model
of the Weyl medium and study its electromagnetic response by a combination of
analytical and numerical techniques. We confirm the existence of the anomalous
Hall effect expected on the basis of the field theory treatment. We find,
contrary to the latter, that chiral magnetic effect (that is, ground-state
charge current induced by the applied magnetic field) is absent in both the
semimetal and the insulator phase. We elucidate the reasons for this
discrepancy.
