4. CONCLUSIONS
High-level quantum calculations were performed to study ground and excited states of endohedral M@C20H20 (M = Li, Na, Mg+). Ground state of each Li@C20H20, Na@C20H20, and Mg@C20H20+ has an electron in a pseudo spherical s-type orbital positioned around Li@C20H20+, Na@C20H20+, and Mg@C20H202+ skeletons. In excited states they populate higher angular momentum p-, d-, f-, g-type superatomic orbitals. Excited states of Li@C20H20 were investigated under several basis sets. M:cc-pVTZ, C:cc-pVTZ, H:d-aug-cc-pVTZ combination accurately represent ground and excited electronic structures of these superatoms. The proposed shell model of Li@C20H20 and Na@C20H20 is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 2f. The series of Mg@C20H20+ is 1s, 1p, 1d, 2s, 1f, 2p, 2d, 1g, 3s, 2f, 2g, 3p. Excitation energies of Li@C20H20 are bigger than Na@C20H20 but lower compared to the Mg@C20H20+. We believe these findings will be useful for future studies on similar superatomic systems.