Electronic structure ofLi12Si7

Abstract

Ab initio localized-spherical-wave calculations on crystalline Li 12 Si 7 are reported. The crystal consists of two one-dimensional units, ͑Li 6 Si 5 ͒ ϱ and ͑Li 12 Si 4 ͒ ϱ , that contain five-membered Si rings and four-membered Si stars, respectively. In the density of states the region below Ϫ5 eV is largely determined by the local ringlike and starlike arrangements of the Si atoms; above Ϫ5 eV there is a signature of delocalization of states across the subunits. Additional calculations on the separate units show that Li 12 Si 7 can be described as ͓Li 12 Si 4 ͔ 4ϩ ͓Li 6 Si 5 ͔ 2 2Ϫ where the charge transfer places the Fermi energy in the gaps of the aromatic subunits. A simple molecular orbital model is presented in order to rationalize the occurrence of these gaps. A short comparison to the theoretical density of states of liquid Li 12 Si 7 is also presented.

Electronic structure of LiSi

“…Therefore, we think that the Li atom in LiSi is an anion with an excess charge of 0.83-0.84. Similarly, the number of electrons within the Si atom region in LiSi was estimated as 3.84-3.85 electrons within the Wigner Seitz radius The negatively charged Li atom also appeared from the DFT calculations of Li 6 Si 5 , which is one of subunits in crystalline Li 12 Si 7 , where the Li atom has an excess charge of 0.9 electrons [29]. The formation of Li anion in LiSi contrasts starkly with the DFT calculation results that the Li atom in the graphene loose 0.76 electrons when compared to the Si anodes and the graphite anodes in LIBs [30].…”

Structural and dynamic characterization of Li12Si7 and Li12Ge7 using solid state NMR

“…With regard to the bonding state of the lithium ions various calculations with different degrees of sophistication and quantitative evaluation have been published previously [8,[16][17][18][19], indicating significant variations in the amount of charge situated on the lithium. Specifically, the Li6 species situated directly above the five-membered Si 5 and Ge 5 rings (labeled Li8 in Ref.…”

“…In approaching resonance assignments, previous electronic structure calculations [8,[16][17][18][19] as well as the proximity and orientation of the various lithium sites with respect to these Si structural moieties must be considered. Table 2 indicates that most lithium species have closest distances to silicon atoms belonging to both the Si 5 rings and the Si 4 stars.…”

“…[1], the structures of all the lithium silicides can be viewed in terms of an extended Zintl-Klemm-Busmann concept, where the excess electrons occupy cage orbitals formed by Li-2s states, surrounding the silicon structural elements in the framework. In Li 12 [16][17][18][19]. In order to gain deeper insights into the structure and bonding in Li 12 Si 7 , the present study reports a comprehensive solid state NMR characterization of the silicide framework using 29 Si MAS-NMR, aided by 2-D J-resolved, radio frequency driven recoupling (RFDR) and { 7 Li} 29 Si cross-polarization-heteronuclear correlation experiments.…”

Electronic Variations in Carbonate- and Phosphane-Related 24- and 26-Electron E4 Clusters of Silicon and Germanium

“…However, this compound does not contain the E 4 stars. [9] Finally an ab initio localized-spherical-wave calculation on crystalline Li 12 Si 7 by van Leuken et al [11] provided new insights into the compound and supported a description similar to model (B) with a planar [Si 4 8À ] ion, which had first been suggested by Schnering et al [2] The main difference to the latter was that in the picture generated by van Leuken et al two electrons less reside in the Si 5 [12] the formulation of a [Si 4 8À ] ion seems to be quite reasonable. The novel ternary Zintl phases M 5x Mg 18Àx E 13 (M Sr, Ba, E Si, Ge), which are isotypic (although the strontium compounds have a slightly different ratio of earth alkaline metals), exclusively contain planar E 4 clusters and thus allow an independent test of the results of the recent calculation on Li 12 Si 7 .…”