Multicentered effective group potentials: ligand-field effects in organometallic clusters and dynamical study of chemical reactivity

A new multicentered effective group potential (EGP) is obtained for η⁶-benzene. Applications on $\hbox{Ru}_{4}(\hbox{H})_{4}(\hbox{C}_{6}\hbox{H}_{6})_{4}]^{n+}$ clusters (n = 0 or 2) are in excellent agreement with reference DFT studies in terms of geometries, energies and electronic structures. In particular, the small singlet–triplet energy difference (3.8 kcal mol^?1) in Ru₄(H)₄(C₆H₆)₄]²⁺ is very well reproduced. This new EGP is nevertheless not free from the limitations associated to this first generation of molecular pseudopotentials. A cautious analysis of the nature and exact role of this EGP is made, which provides new directions for the elaboration of the next generation of EGPs. In addition, the η⁵-cyclopentadienyl EGP has been used to perform a constrained dynamical simulation for the reaction of Cp₂LaH with H₂. The energy conservation during the simulation as well as the activation barrier extracted from the simulation clearly demonstrate the good behavior of this EGP in the context of molecular dynamics. Anharmonic effects on this reaction are underlined, further demonstrating the high accuracy of the potential energy surface obtained with EGPs. From a more general point of view, such EGPs are expected to provide accurate albeit low-cost ligand-field effects in organometallic clusters or nanoparticles and to allow dynamical studies at the surface of such compounds.