  Weyl semimetal is a new phase of matter that provides the first solid state
realization of chiral Weyl fermions. Most of its unique physics is a
consequence of chiral anomaly, namely nonconservation of the number of
particles of a given chirality. Mathematically, this is expressed in the
appearance of the so called $\theta$-term in the action of the electromagnetic
field, when the Weyl fermions are integrated out. Recently, however, it has
been suggested that the analogy between the chiral fermions of quantum field
theory with unbounded linear dispersion, and their solid state realization with
a dispersion naturally bounded by the bandwidth and crystal momentum defined
only within the first Brillouin zone, holds only in a restricted sense, with
parts of the $\theta$-term absent. Here we demonstrate that this is not the
case. We explicitly derive the $\theta$-term for a microscopic model of a Weyl
semimetal by integrating out fermions coupled to electromagnetic field, and
show that the result has exactly the same form as in the case of relativistic
chiral fermions.
