  The standard assumption for the equilibrium microcanonical state in quantum
mechanics, that the system must be in one of the energy eigenstates, is
weakened so as to allow superpositions of states. The weakened form of the
microcanonical postulate thus asserts that all quantum states giving rise to
the same energy expectation value must be realised with equal probability. The
consequences that follow from this assertion are investigated. In particular, a
closed-form expression for the density of states associated with any system
having a nondegenerate energy spectrum is obtained. The result is applied to a
variety of examples, for which the behaviour of the state density, as well as
the relation between energy and temperature, are determined. Numerical studies
indicate that the density of states converges to a distribution when the number
of energy levels approaches infinity.
