  We study dynamical dark energy models within Einstein's theory by means of
matter perturbations and the growth index $\gamma$. Within four-dimensional
General Relativity, we assume that dark energy does not cluster, and we adopt a
linear ansatz for the growth index to investigate its impact on the
deceleration parameter, $q$, and on the dark energy equation-of-state
parameter, $w$. Following this approach, we identify a relationship between
$q_0$ (today's value of $q$) and $\gamma$, which to the best of our knowledge
is new. For $w(z)$, we find that in most of the cases considered it crosses the
-1 line (quintom) ending at a present day value $w_0 > -1$. Furthermore, we
show that an analytic expression for $w(z)$ may be obtained in the form of
order (4,4) (or higher) Pad{\'e} parameterizations.
