Acceleration of rovibrational spectrum calculations through sparsity techniques

The variational calculation of microwave or high-resolution rovibrational spectra is hampered by large memory requirements and long computation times. Simple sparsity techniques, the explicit account of symmetry, and different rotational basis functions have been employed to reduce these computational demands without deteriorating the final spectra. The dependence of the sparsity of the eigenvectors of the rovibrational Hamiltonian matrix with respect to the completeness of the Watson operator has been studied in detail. Benchmark calculations are provided for thioformaldehyde, thioformyl cyanide, and thiopropynal.