Interaction of manganese with single-wall ${\mathrm{B}}_2\mathrm{O}$ nanotubes: An ab initio study

Interaction of a manganese atom with a graphitic ${\mathrm{B}}_2\mathrm{O}$ sheet and a (3,0) single-wall ${\mathrm{B}}_2\mathrm{O}$ nanotube was investigated using first-principles spin-polarized density functional calculations. The stable geometries, electronic and magnetic properties of the Mn-doped planar and tubular systems were analyzed. It was found that the most stable adsorption site is above the hole site for the ${\mathrm{B}}_2\mathrm{O}$ sheet. For the (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube, when the Mn atom is adsorbed outside the tube, the most energetically favorable site is the center of the hexagon with an axial symmetry, followed by the bridge site above the axial $\mathrm{B}\text{−}\mathrm{B}$ bond. The magnetic moment of the Mn-doped nanotube is similar to that of the free Mn atom. The atop oxygen site, however, is the most stable site if the Mn atom is inside the tube. In this case, the Mn atom is seven-coordinated and the nanotube is significantly distorted, leading to a larger binding energy and a smaller magnetic moment of $\sim 1{\mu }_B$.

Figure 1

(Color online) Different adsorption sites for a single Mn atom on the graphitic ${\mathrm{B}}_2\mathrm{O}$ sheet and the (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube. The dashed region indicates the unit cell of the graphitic ${\mathrm{B}}_2\mathrm{O}$ sheet. For the ${\mathrm{B}}_2\mathrm{O}$ sheet, the axial and zigzag sites are equivalent, namely, $H_a\iff H_z$, $T\text{−}2{\mathrm{B}}_a\iff T\text{−}2{\mathrm{B}}_z$, $A\text{−}\mathrm{BB}\iff Z\text{−}\mathrm{BB}$, and $A\text{−}\mathrm{BO}\iff Z\text{−}\mathrm{BO}$.

Figure 2

Band structures of (a) the clean graphitic ${\mathrm{B}}_2\mathrm{O}$ sheet; (b) the majority spin, and (c) the minority spin for Mn adsorption at the $H$ site on ${\mathrm{B}}_2\mathrm{O}$ sheet. The Fermi level is indicated by the dashed line.

Figure 3

Projections of local density of states onto (a) the $\mathrm{Mn}3d$ orbital, (b) the $\mathrm{Mn}4s$ orbital, (c) the ${\mathrm{B}}_{a}2p$ orbital, (d) the ${\mathrm{B}}_{b}2p$ orbital, (e) the ${\mathrm{B}}_{c}2p$ orbital, for Mn adsorption at the $H$ site on ${\mathrm{B}}_2\mathrm{O}$ sheet. Atoms ${\mathrm{B}}_a$, ${\mathrm{B}}_b$, and ${\mathrm{B}}_c$ are labeled in Fig. 1.

Figure 4

(Color online). (a) The relaxed structure of the ${\mathrm{B}}_2\mathrm{O}$ nanotube with a Mn atom adsorbed at the $H_a$ site. The spin density isosurfaces correspond to (b) $0.02e∕{\mathrm{\AA }}^3$, and (c) $-0.01e∕{\mathrm{\AA }}^3$ for the same configuration.

Figure 5

Band structures of (a) the pure (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube; (b) the majority spin, and (c) the minority spin of Mn adsorption at the $H_a$ site on the outer wall of the (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube. The Fermi level is indicated by the dashed line.

Figure 6

Projections of local density of states onto (a) the $\mathrm{Mn}3d$ orbital, (b) the $\mathrm{Mn}4s$ orbital, (c) the $2s$ orbital, and (d) the $2p$ orbital of boron atom $1$, (e) the $2s$ orbital, and (f) the $2p$ of boron atom 2, for Mn adsorption at the $H_a$ site on the outer wall of the (3.0) ${\mathrm{B}}_2\mathrm{O}$ nanotube. Boron atoms 1 and 2 are shown in Fig. 4a.

Figure 7

(Color online) Top view (a) and side view (b) [along the direction indicated by the arrow in (a)] of the relaxed (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube with a Mn atom adsorbed at $A\text{−}\mathrm{BB}$, where the Mn atom is encapsulated inside the tube without chemically bonding to any atoms.

Figure 8

(Color online) (a) The relaxed structure of the (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube with a Mn atom adsorbed at the $T\text{−}\mathrm{O}$ site inside the tube wall. The spin density isosurfaces corresponding to (b) $0.015e∕{\mathrm{\AA }}^3$, and (c) $-0.025e∕{\mathrm{\AA }}^3$, respectively, for the same configuration.

Figure 9

The projected local density of states onto (a) the $\mathrm{Mn}3d$ orbital; (b) the $\mathrm{Mn}4s$ orbital, and (c) the $2p$ orbital of the oxygen atom which is bonded to the Mn atom for a single Mn atom adsorbed at the $T\text{−}\mathrm{O}$ site inside the (3,0) ${\mathrm{B}}_2\mathrm{O}$ nanotube.