  The thermoelectric power S is studied within the one-dimensional Hubbard
model using the linear response theory and the numerical exact-diagonalization
method for small systems. While both the diagonal and off-diagonal dynamical
correlation functions of particle and energy current are singular within the
model even at temperature T>0, S behaves regularly as a function of frequency
$\omega$ and T. Dependence on the electron density n below the half-filling
reveals a change of sign of S at n_0=0.73+/-0.07 due to strong correlations, in
the whole T range considered. Approaching half-filling S is hole-like and can
become large for U>>t although decreasing with T.
