  We construct a finite bath with variable temperature for quantum
thermodynamic simulations in which heat flows between a system $\mathcal{S}$
and the bath environment $\mathcal{E}$ in time evolution of an initial
$\mathcal{SE}$ pure state. The bath consists of harmonic oscillators that are
not necessarily identical. Baths of various numbers of oscillators are
considered; a bath with five oscillators is used in the simulations. The bath
has a temperature-like level distribution. This leads to definition of a
system-environment microcanonical temperature $T_\mathcal{SE}(t)$ which varies
with time. The quantum state evolves toward an equilibrium state which is
thermal-like, but there is significant deviation from the ordinary
energy-temperature relation that holds for an infinite quantum bath, e.g. an
infinite system of identical oscillators. There are also deviations from the
Einstein quantum heat capacity. The temperature of the finite bath is
systematically greater for a given energy than the infinite bath temperature,
and asymptotically approaches the latter as the number of oscillators
increases. It is suggested that realizations of these finite-size effects may
be attained in computational and experimental dynamics of small molecules.
