Effects of vibrational anharmonicity and inter-mode couplings on the binding energy of a positron to molecules

We theoretically analyzed the effect of the anharmonicity and the inter-mode couplings of molecular vibrations on a positron affinity (PA), which is the binding energy of a positron, of HCN and CH₂O molecules. Based on the different theoretical approaches for describing vibrational wave functions, we confirmed that (i) not only the anharmonicity but also the inter-mode couplings on potential energy surface are indispensable for the accurate calculation of PA values, and (ii) the effect of inter-mode couplings on a positron affinity surface is sufficiently weaker than that on potential energy surface. (paper)