On the Potential of Using the Al₇ Superatom as an Excess Electron Acceptor To Construct Materials with Excellent Nonlinear Optical Properties

Abstract

With the aid of density functional theory (DFT) calculations, we found that, when alkali metal approaches the Al7 superatom, its outermost s-value electron can be trapped by Al7 to give the superatom compound MAl7 (M = Li, Na, K) with an excess electron. Different analyses including natural bond orbital (NBO), electron localization function (ELF), and energy decomposition analysis (EDA) show that the resulting M-Al bond is strong and has a polar covalent character. The optimizations of self-assemblies (MAl7)n (n = 2, 3) have been performed to explore the stability of MAl7 in the solid state. The results reveal that only NaAl7 can keep its structural integrity as a building block upon self-assembling, while serious aggregations between Al7 clusters occur in the dimers and trimers of LiAl7 and KAl7, despite the fact that the Li-Al7 and K-Al7 bond energies are comparable to that of Na-Al7. Born-Oppenheimer molecular dynamics (BOMD) simulations for (NaAl7)n (n = 2, 3) indicate that these species are stable toward fragmentation at 300 K. The β0 values of (NaAl7)n (n = 1, 2, and 3) predicted at the CAM-B3LYP/6-311+G(3df) level of theory are in the range of 1.6 × 10(4)a.u. to 7.5 × 10(4) a.u.. This theoretical study implies that NaAl7 is a promising candidate for nolinear optical (NLO) materials. We provide theoretical evidence for the possibility of using the Al7 superatom as an excess electron acceptor to construct materials with excellent NLO properties. Further experimental research is invited.

Distinctive Characteristics of Al7Li: A Superatom Counterpart of Group IVA Elements

“…As presented in Table , the HOMO–LUMO gaps of the Al 7 Li isomers are in the range of 1.30–1.86 eV, which are comparable to that of Al 7 – superatom (1.62 eV, computed at the same level), indicating stability and chemical inertness of the studied species . Binding energy per atom ( E a ) of these Al 7 Li structures, which is defined as was measured at the CCSD­(T)//B3LYP/6-311+G­(3df) level.…”

“…Vibrational frequency analysis was carried out at the same level. The combination of B3LYP functional with the 6-311+G­(3df) basis set was chosen in this work because it has performed well in characterizing both lithium- and aluminum-based clusters. ,,,− The initial structures of superatom compounds (Al 7 Li)­M (M = Li, Be, B, C, N, O, and F), (Al 7 Li)­F n ( n = 1–6), and (Al 7 Li)­H 4 were built on the basis of the first and second lowest-energy structures of Al 7 Li because these two isomers have quite small energy difference (0.41 kcal/mol). The additional atoms (M, F, and H) were placed at all possible positions either inside or on the surface of the Al 7 Li cage.…”

“…Over the past decades, a considerable number of experimental and theoretical investigations have been carried out to design superatoms and relate them to a certain element or group in the periodic table. Excitingly, various superatoms such as superalkalis, − superalkaline-earth-metal atom, superhalogens, ,− multivalent superatom, quasi-phosphorus superatom, and even magnetic superatoms − have been identified to date. Very recently, Sun et al have presented another new member to the superatom family, namely Al 12 Be, which shares a lot of similarity with chalcogen elements.…”

Superatom Compounds under Oriented External Electric Fields: Simultaneously Enhanced Bond Energies and Nonlinear Optical Responses

“…Up to now, a large number of novel compounds using superatoms as building blocks have been synthesized and characterized by experimental and theoretical workers. ,,,− Among them, the “supersalts”, − a special kind of superatom compounds formed by combining superalkalis and superhalogens, have attracted great interests because of their potential applications in nonlinear optical (NLO) materials, , high energy density materials, energy storage and energy conversion materials . For example, Khanna and co-workers have theoretically constructed a new type of unique superatom compound by combining superhalogen Al 13 and superalkalis (K 3 O and Na 3 O) .…”

Computational screening of carbon monoxide (CO) adsorption over neutral and charged Al7 clusters

“…Certain aluminum clusters show superatom properties. For example, Al 7 is known as superatom and its potential to construct excellent non-linear optical materials has been investigated [14]. Anionic Al clusters (Al n − with n = 1, 2, 3, …) also have superatomic properties [15, 16].…”