Theoretical study of isoelectronicSinMclusters (M=Sc−,Ti

Abstract

We study, from first-principles quantum mechanical calculations, the structural and electronic properties of several low-lying energy equilibrium structures of isoelectronic Si n M clusters ͑M =Sc − ,Ti,V + ͒ for n = 14-18. The main result is that those clusters with n = 16 are more stable than its neighbors, in agreement with recent experimental mass spectra. By analyzing the orbital charge distribution and the partial orbital density of states, that special stability is rationalized as a combination of geometrical ͑near spherical cagelike structure for n =16͒ and electronic effects ͑l-selection rule of the spherical potential model͒. The structures of the two lowest energy isomers of Si 16 M are nearly degenerate, and consist of the Frank-Kasper polyhedron and a distortion of that polyhedron. The first structure is the ground state for M =V + , and the second is the ground state for Ti and Sc − . For the lowest energy isomers of clusters Si n M with n = 14-18, we analyze the changes with size n, and impurity M of several quantities: binding energy, second difference of total energy, HOMO-LUMO gap, adiabatic electron affinity, addition energy of a Si atom, and addition energy of an M impurity to a pure Si n cluster. We obtain good agreement with available measured adiabatic electron affinities for Si n Ti.

Structural Identification of Caged Vanadium Doped Silicon Clusters

“…The absorption bands in the IR-MPD spectrum of Si 15 V þ Á Xe match the vibrational modes of a structure based on a combination of 2 pentagons and 10 rhombuses, which was located as the ground state in agreement with earlier predictions for Si 15 V þ [10,15] and the isoelectronic Si 15 Ti [15,37]. Vibrational spectra of hexagonal prism based structures, such as found in some studies [38], do not match the IR-MPD spectrum [34].…”

“…Computationally, several isomers of Si 14 V þ were located close in energy (five isomers within 0.1 eV) [34]. In line with an earlier study [15], most low energy isomers have singlet electronic states and are constructed by addition of two Si atoms to various sites of a DHP and subsequent structural relaxation. Although the lowest energy isomer (shown in Fig.…”

“…Si 16 V þ is predicted to have a symmetric FK polyhedral structure [10,15,39]. Its stability was rationalized by means of an electron counting rule.…”

“…Most interestingly, it is predicted that transition-metal atoms possibly stabilize the clusters and induce the formation of symmetric endohedral cages with the dopant atom at the center of the cage, which is of relevance for novel silicon based nanostructured devices [8][9][10][11][12]. For example, fullerenelike cages and Frank-Kasper (FK) polyhedrons, which are tetrahedrally close-packed structures containing interpenetrating polyhedra with coordination numbers 12, 14, 15, or 16 [13], are predicted for Ti and V doped silicon clusters with at least 12 Si atoms [10,14,15]. However, if there are insufficient Si atoms to fully enclose the dopant atom, basketlike structures are formed [11].…”

Magnetic silicon fullerene

“…On the theoretical side, there have been 30 many first-principles investigations of silicon clusters with 8-20 atoms encapsulating 3d, 4d and 5d metal atoms. [5][6][7][8][9][10][11] It is known that the smallest carbon fullerene cage is C 20 with a dodecahedral structure. [12,13] [19] Very recently, studies of the 45 photoelectron spectra of EuSi n cluster anions ( 17…”