Describing Molecular Spin

In the past decade Variational Monte Carlo has been used to accurately calculate the vibrational energies of several small molecules. The trial wavefunctions used in these fully nonadiabatic calculations are simple and contain a relatively small number of adjustable parameters. In contrast, the calculation of rotational states has been less successful; the Monte Carlo results show a small but significant deviation when compared with the best explicitly correlated basis set calculations. This talk proposes a possible reason for this discrepancy and how the solution to this problem can lead to better descriptions of how molecules spin.