  We develop the variational-cluster-approximation method based on the
thermal-pure-quantum-state approach and apply the method to the calculations of
the thermodynamic properties of the Hubbard model, thereby obtaining the
temperature dependence of the single-particle excitation spectra, entropy and
specific heat, and order parameter of the antiferromagnetic phase efficiently.
We thus demonstrate that the method developed here has a potential power for
elucidating finite-temperature properties of strongly correlated electron
systems.
