First-principles calculations of hyperfine structure in M -doped Si 16 H 16 fullerene cages ( M = Cr , Mn, and Fe)
First-principles calculations of hyperfine structure in M -doped Si 16 H 16 fullerene cages ( M = Cr , Mn, and Fe)
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DOI：
10.1103/physrevb.79.235443
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发表时间：
2009-06
影响因子：
3.7
通讯作者：
M. Bahramy;Vijay Kumar;Y. Kawazoe
中科院分区：
文献类型：
--
作者：
M. Bahramy;Vijay Kumar;Y. Kawazoe
利用密度泛函理论计算方法研究了${\text{Si}}_{16}{\text{H}}_{16}$富勒烯内嵌掺杂过渡金属原子$M=\text{Cr}$、Mn和Fe的磁性和超精细结构。在所有情况下，内嵌富勒烯都保持与自由原子相同的磁矩，并且它主要定位在$M$上，部分重新分布在${\text{Si}}_{16}{\text{H}}_{16}$笼上。然而，将$M$掺杂剂的各向同性超精细参数${a}_{\text{iso}}$与自由$M$原子的参数${a}_{\text{iso}}$进行比较，发现Mn和Fe在${\text{Si}}_{16}{\text{H}}_{16}$笼中掺杂后，原子核处的电子波函数在数量和质量上都发生了显著的变化，而Cr则几乎保持不变。Mn和Fe原子的内面体掺杂增加了$M$原子原子核处的自旋密度${\ensuremath{\rho}}_{s}({\mathbf{R}}_{M})$的值，相应地增加了${A}_{\text{iso}}$的值。分析了单占据分子轨道（SOMOs）诱导核心自旋极化的趋势，表明Mn和Fe原子的${A}_{\text{iso}}$值的增加直接来自于SOMOs对${\ensuremath{\rho}}_{s}({\mathbf{R}}_{M})$的贡献增加，间接来自于掺杂剂的$3d$轨道与笼的$s$和$p$类轨道的杂化。后者导致核心$2s$和$3s$轨道的自旋极化减小，从而使它们对${\ensuremath{\rho}}_{s}({\mathbf{R}}_{M})$的贡献减小。这些结果可能具有更广泛的适用性，并可能提供一种识别内源性掺杂的方法。
We study magnetism and hyperfine structure in ${\text{Si}}_{16}{\text{H}}_{16}$ fullerenes endohedrally doped with a transition-metal atom $M=\text{Cr}$, Mn, and Fe using density functional theory calculations. In all cases the endohedral fullerene maintains the same magnetic moment as in a free $M$ atom and it is mainly localized on $M$ with partial redistribution on the ${\text{Si}}_{16}{\text{H}}_{16}$ cage. However, a comparison between the isotropic hyperfine parameter ${A}_{\text{iso}}$ of $M$ dopants with that of free $M$ atoms reveals that the electronic wave function at the nucleus of Mn and Fe undergo a significant change both quantitatively and qualitatively as they become doped inside ${\text{Si}}_{16}{\text{H}}_{16}$ cage, while for Cr it remains nearly the same. The endohedral doping of Mn and Fe atoms increases the value of the spin density at the nucleus of the $M$ atom, ${\ensuremath{\rho}}_{s}({\mathbf{R}}_{M})$ and correspondingly, the value of ${A}_{\text{iso}}$. Analyzing the trend of the core spin-polarization induced by the singly occupied molecular orbitals (SOMOs), it is shown that the increase in the value of ${A}_{\text{iso}}$ for Mn and Fe atoms comes directly from an increase in the contribution of SOMOs to ${\ensuremath{\rho}}_{s}({\mathbf{R}}_{M})$ and indirectly from hybridization of $3d$ orbitals of the dopants with the $s$- and $p$-like orbitals of the cage. The latter results in a decrease in the spin-polarization of the core $2s$ and $3s$ orbitals so that they less effectively contribute to ${\ensuremath{\rho}}_{s}({\mathbf{R}}_{M})$. These results are likely to have wider applicability and could offer a way to identify endohedral doping.