Bonding properties and isomeric conversion pathways from exohedral to endohedral BeGe8 clusters

► A cubic Be@Ge8 ground state was found after B3LYP/6-31G* optimizations. ► Be hypervalency and Be-Ge covalency were ratiocinated from back-donation. ► The 6-311++G(3df) energies concluded a C2v Be@Ge8 as the ground state. ► Found the number of Be-Ge and Ge-Ge bonds compete to affect cluster stabilities. ► Conversion pathways from exohedral BeGe8 to Be@Ge8 were illustrated.