Theoretical Investigation of Geometry and Stability of Small Lithium-Iodide Li_nI (n = 2-6) Clusters

摘要

We present theoretical investigation of the structural characteristics and stabilities of neutral and positively charged Li_nI (n = 2-6) species. The structural isomers were found by using a randomized algorithm to search for minima structures, followed by B3LYP optimizations; the single-point RCCSD(T)/ccpwCVTZ(-PP) calculations were performed in order to compute relative energies, binding energies per atom, adiabatic and vertical ionization energies, and dissociation energies. Stability was compared to the pure lithium clusters; there is a typical odd-even alternation; iodine doped clusters are more stable than pure lithium clusters. Lithium "cage" transfers its valence electron to the iodine atom to form neutral I~-2-Li_n~+ and cationicI~--Li_n~(2+) clusters. An electron departures the lithium cage upon ionization. An important reason for the larger stability of closed-shell species is the existence of the HOMO 3c/2e natural bond orbitals.