Quantum chemical vibrational analysis of clusters providing an explanation for the planarity of the P 64− ring

Abstract

Equilibrium geometry and vibrational frequencies were calculated for a planar and hexagonal P 6 4− ring, as a free anion and as situated in different clusters with the same D 6 h symmetry as the ring. The results show that the planarity is not a consequence of an inherent stability of the planar ring. The planarity is maintained only if the ring is sandwiched between two hexagons of counterions, and is therefore partly a consequence of the electrostatic field set up by the counterions. The sizes of the clusters, and the large numbers of electrons involved, make the calculations one of the most resource demanding HF ab initio vibrational analyses performed to date. Still the results show that even the largest model chosen is too small to give an accurate description of the system.