  The nuclear energy density functional method at finite temperature is a
useful tool for studies of nuclear structure at high excitation, and also for
researches of nuclear matter involved in explosive stellar phenomena and
neutron stars. However, its unrestricted calculation requires large
computational costs for the three-dimensional coordinate-space solvers,
especially for the Hamiltonian matrix diagonalization and (or) the Gram-Schmidt
orthonormalization of the single-particle wave functions. We test numerical
performance of the Fermi operator expansion method, that requires neither the
diagonalization nor the Gram-Schmidt orthonormalization, for finite nuclei and
inhomogeneous nuclear matter. The method is applied to isolated finite N=Z
nuclei and to non-uniform symmetric nuclear matter at finite temperature, which
turns out be very effective with the three-dimensional coordinate-space
representation, especially at high temperature. The Fermi operator expansion
method is a useful tool for studies of various nuclear phases at finite
temperature with the energy density functional calculations. The method is
suitable for massively parallel computing with distributed memory. Furthermore,
when the space size is large, the calculation may benefit from its order-N
scaling property.
