  Thermodynamical properties of canonical and grand-canonical ensembles of the
half-filled two-site Hubbard model have been discussed within the framework of
the nonextensive statistics (NES). For relating the physical temperature $T$ to
the Lagrange multiplier $\beta$, two methods have been adopted: $T=1/k_B \beta$
in the method A [Tsallis {\it et al.} Physica A {\bf 261} (1998) 534], and
$T=c_q/k_B \beta$ in the method B [Abe {\it et al.} Phys. Lett. A {\bf 281}
(2001) 126], where $k_B$ denotes the Boltzman constant, $c_q= \sum_i p_i^q$,
$p_i$ the probability distribution of the $i$th state, and $q$ the entropic
index. Temperature dependences of specific heat and magnetic susceptibility
have been calculated for $1 \lleq q \lleq 2$, the conventional Boltzman-Gibbs
statistics being recovered in the limit of $q = 1$. The Curie constant
$\Gamma_q$ of the susceptibility in the atomic and low-temperature limits ($t/U
\to 0, T/U \to 0$) is shown to be given by $\Gamma_q=2 q 2^{2(q-1)}$ in the
method A, and $\Gamma_q=2 q$ in the method B, where $t$ stands for electron
hoppings and $U$ intra-atomic interaction in the Hubbard model. These
expressions for $\Gamma_q$ are shown to agree with the results of a free spin
model which has been studied also by the NES with the methods A and B. A
comparison has been made between the results for canonical and grand-canonical
ensembles of the model.
