Can the cosmological dark sector be modeled by a single scalar field?
  In a previous paper it was shown that a minimally coupled scalar field of
mass $M \sim H_0$ can describe both components of the dark sector in a unified
way. In the solution found, the dark energy component decays linearly with the
Hubble parameter, with a homogeneous creation of dark matter. In the present
note we show that a $\Lambda$CDM dark sector can also be modeled by such a
single field. More generally, we show that the system of Klein-Gordon and
Einstein equations admits a uniparametric family of solutions that is
equivalent to a non-adiabatic (with zero sound speed) generalised Chaplygin
gas.
