The molecular and electronic structure of Li 5B 4

Abstract

Based on a molecular structure characterized earlier, a molecular orbital calculation was made on Li 5B 4. The electronic structure of Li 5B 4 thus calculated shows (1) a partial electron charge transfer of about 0.35 eu from a five-lithium-atom cluster (at an energy level E′) to a four-boronatom cluster (also at an energy level E′) is necessary to stabilize the Li 5B 4 molecular structure and (2) the stabilization energy based on the electrostatic interaction using a multipole expansion amounts to 2 eV per fourboron-atom unit or equivalent to 1.06 kcal (gm B) −1. From the experimental fact that the Li 5B 4 compound alloy is a metallic conductor, the remaining 0.65 eu charges in the five-lithium-atom cluster at an energy level E′ are assumed to delocalize and to become “free” electrons. This delocalization yields an additional energy of 1.70 kcal (gm B) −1. The calculated total stabilization energy is therefore 2.76 kcal (gm B) −1 compared with the experimental value of 2.2 ± 0.2 kcal (gm B) −1.