On using low-order Hermite interpolation in `direct dynamicsʹ calculations of vibrational energies using the code `MULTIMODEʹ

We present and test a reduced, piecewise Hermite algorithm to interpolate ab initio potential and gradient data for use in the code MULTIMODE, which does rovibrational calculations of polyatomic molecules. The procedure is tested for H2CS, for which we have an analytical six-dimensional potential energy surface. This surface is used to generate potential and gradient data in order to mimic the interface between MULTIMODE and electronic structure packages. Exact results are also obtained with this potential to provide benchmarks to test the accuracy of the new interpolation procedure.