Theoretical Studies Of Superatom Compounds Al₁₄X And TM@Si₁₆-TCNQ

Superatoms,stable clusters with well-defined size and composition which could mimic the chemical behavior of atoms in the Periodic Table,could also act as fundamental building blocks to construct novel compounds or even materials.The main contribution of this thesis is summarized as follows:1.A new series of superalkaline-earth-metal compounds Al₁₄X?X=F₂,Cl₂,Br₂,I₂,?OH?₂,O,S?has been investigated at the TPSS/Def2-TZVPP level.It is found that both interaction position and mode between Al₁₄ and X ligands influence isomer stability of the resulting superatom compounds.On the one hand,the top and bottom sites of Al₁₄ have higher reactivity relative to middle ones.On the other hand,different ligands favor different binding patterns when combining with Al₁₄.For example,the halogen ligands prefer to occupy on-top sites of Al₁₄.In contrast,the end-on bound configurations are the least favorable for Al₁₄ oxide.NPA analysis indicates that the Al₁₄ cluster donates electrons to X ligands.AIM analysis also suggests ionic bond character of the connection?s?between Al₁₄ and X moieties.Thus,the Al₁₄X compounds are much like divalent salts where superatom Al₁₄ behaves just like an alkaline-earth-metal atom.Furthermore,considerable dissociation energies and large HOMO-LUMO gaps confirm stability of these superatom compounds.2.By combining quasi-alkali-metal superatom TM@Si₁₆?TM=V,Nb,Ta?and strong electron-acceptor tetracyanoquinodimethane?TCNQ?,a series of superatom compounds TM@Si₁₆-TCNQ were theorectically designed and studied.NPA analysis indicates that TM@Si₁₆-TCNQ is a new type of charge-transfer compound where TM@Si₁₆ carries positive charge.Positive dissociation energies and large HOMO-LUMO gaps confirm the stability of these compounds.Furthermore,for superatom compounds TM@Si₁₆-TCNQ,most of the TM@Si₁₆-TCNQ compounds exhibit large first hyperpolarizability values?29821.4-62147.3 a.u.?,indicating that these species possess considerable nonlinear optical?NLO?response.