  In the present work we introduce a computational approach to the absolute
rovibrational quantum partition function using the path-integral formalism of
quantum mechanics in combination with the nested sampling technique. The
numerical applicability of path-integral nested sampling is demonstrated for
small molecules of spectroscopic interest. The computational cost of the method
is determined by the evaluation time of a point on the potential-energy surface
(PES). For efficient PES implementations, the path-integral nested-sampling
method can be a viable alternative to the direct Boltzmann summation technique
of variationally computed rovibrational energies, especially for medium-sized
molecules and at elevated temperatures.
