Multiple K-shell excitation of lithium clusters: Implications for hollow-atom solids

Systematic molecular-orbital calculations are performed for Li 9 z + clusters in which Nexc (=0–9) core electrons are excited to valence orbitals. For neutral (z = 0) clusters, the magnitudes of work functions, cohesive energies, and average core-electron excitation energies increase with Nexc, owing to relaxation of valence electrons around localized core holes. Total energy of a multiply charge ion, produced by a series of Auger decay, remains lower than the corresponding dissociation limit as far as z ⩽ 3. We thereby discuss a possibility of realizing a hollow-atom solid, multiply core-excited state with temporal crystalline order, by utilizing intense free-electron lasers.