  Pairwise entanglement, calculated separately for charge and spin degrees of
freedom, is proposed as a ground-state signature of the Mott transition in
correlated nanoscopic systems. Utilizing the exact diagonalization - ab initio
method (EDABI), for chains containing $N\leqslant{}16$ hydrogenic-like atoms
(at the half filling), we find that the vanishing of the nearest-neighbor
charge concurrence indicates the crossover from a partly-localized quantum
liquid to the Mott insulator. Spin concurrence remains nonzero at the
insulating phase, showing that the decopling of spin and charge degrees of
freedom may manifest itself by wavefunctions entangled in spin, but separable
in charge coordinates. At the quarter filling, the analysis for
$N\leqslant{}20$ shows that spin concurrence vanishes immediately when the
charge-energy gap obtained from the scaling with $1/N\rightarrow{}0$ vanishes,
constituting a finite-system version of the Mott transition. Analytic
derivations of the formulas expressing either charge or spin concurrence in
terms of ground-state correlation functions are also provided.
