  Heat capacities of model systems with finite numbers of effective degrees of
freedom are evaluated using canonical and microcanonical thermodynamics.
Discrepancies between both approaches, which are observed even in the
infinite-size limit, are particularly large in systems that exhibit an
excited-state quantum phase transition. The corresponding irregularity of the
spectrum generates a singularity in the microcanonical heat capacity and
affects smoothly the canonical heat capacity.
