Analysis of the electron density features of small boron clusters and the effects of doping with C, P, Al, Si, and Zn: Magic B₇P and B₈Si clusters

Abstract

Boron atomic clusters show several interesting and unusual size-dependent features due to the small covalent radius, electron deficiency, and higher coordination number of boron as compared to carbon. These include aromaticity and a diverse array of structures such as quasi-planar, ring or tubular shaped, and fullerene-like. In the present work, we have analyzed features of the computed electron density distributions of small boron clusters having up to 11 boron atoms, and investigated the effect of doping with C, P, Al, Si, and Zn atoms on their structural and physical properties, in order to understand the bonding characteristics and discern trends in bonding and stability. We find that in general there are covalent bonds as well as delocalized charge distribution in these clusters. We associate the strong stability of some of these planar/ quasiplanar disc-type clusters with the electronic shell closing with effectively twelve delocalized valence electrons using a disc-shaped jellium model. -B , 9 B 10 , B 7 P, and B 8 Si, in particular, are found to be exceptional with very large gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and these are suggested to be magic clusters.

Smallest Fullerene-like Structures of Boron with Cr, Mo, and W Encapsulation

“…The two bands and the two chains loop around and encapsulate the M atom in a tetrahedral coordination. Such bands are a recurring motif in many kinds of boron clusters, including drums [34,39] and quasiplanar structures. [57] The two bands join each other and the two chains at four tetra-coordinate boron atoms.…”

“…The method of calculation has been discussed earlier. [34] Figure 9 (a) shows the atomic structure with BCPs (green dots) and RCPs (red dots) while (b) shows a symmetrical view of Cr@B 22 along with the electrostatic potential mapped onto a ρ(r) = 0.1e/Bohr 3 electron density isosurface. Blue regions indicate negative electrostatic potential associated with the boron atoms.…”

“…[25] Disk-like or wheel-shaped structures have also been predicted for boron clusters having up to about 11 boron atoms by doping a transition M atom [26,27,28,29,30,31,32,33] as well as other elements. [34] The stability of some disk-shaped clusters has been correlated with electronic shell closing at 12 valence electrons. [34] Further, recently bowl-shaped [35,36,37,38,39] and drum-shaped [40,39] structures of boron have been predicted to be stabilized by M atom dopants such as M@B 14 drum with M = Cr, Fe, Co, and Ni, and also with 16 boron atoms such as Co@B − 16 .…”

“…[34] The stability of some disk-shaped clusters has been correlated with electronic shell closing at 12 valence electrons. [34] Further, recently bowl-shaped [35,36,37,38,39] and drum-shaped [40,39] structures of boron have been predicted to be stabilized by M atom dopants such as M@B 14 drum with M = Cr, Fe, Co, and Ni, and also with 16 boron atoms such as Co@B − 16 . We have studied M atom encapsulated boron clusters in the size range of 18 to 24 atoms in order to find the smallest cage of free boron clusters besides the drum structures.…”

DFT Study on the Structural, Opto-electronic Properties

“…Doping of various atom on boron clusters opens up the possibility of unique boron based nanostructures which contains some intriguing properties [21]. There are many investigations on transition metal doped pyramidal B m nanoclusters [3,[22][23][24][25] which concerns about the stability and bonding mechanism of the clusters. Moreover, transition-metal (TM) dopants (Cr, Mn, Fe, Co, Ni, Zr) can interestingly change the geometry of small boron based nanoclusters [26][27][28].…”