The exohedral doping of a first row transition metal atom (M) on Al₁₂N₁₂ nanocages was performed for assessing the geometric, thermodynamic, electronic and nonlinear optical properties of the doped materials. The transition metals were doped at different positions on the Al₁₂N₁₂ nanocages to yield M@x-Al₁₂N₁₂ (where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and x = b₆₄, b₆₆, r₆, and r₄). The doped nanocages carried transition metal atoms located over the Al–N bond (b₆₄/b₆₆ sites) or above the six (r₆) and four membered ring (r₄). A spin-polarized DFT study revealed that the most stable spin was monotonically increased to a sextet for Mn@x-Al₁₂N₁₂, and then decreased gradually to a singlet for Zn@x-Al₁₂N₁₂. The transition metals atoms were chemisorbed on the Al₁₂N₁₂ nanocages, as revealed from the very high binding enthalpies (−16 to −64 kcal mol⁻¹). The NBO charges and bond orders were analyzed to rationalize the strength and nature of the bonding between the transition metal and nanocage. It was found that, regardless of the doping position and atomic number, the transition metal atoms could significantly lower the HOMO–LUMO gap (E_H–L), by up to 40% of that of pure Al₁₂N₁₂. By applying the long-range separated method, the first hyperpolarizability (β₀) values were calculated. The NLO response of the transition-metal-doped nanocages was comparable to those of their alkali-metal-doped analogs, which is quite remarkable because alkali metal atoms are one of the best inducers of the NLO response. The best NLO response (β₀ = 1.85 × 10⁴ a.u.) was calculated for Cu@r₆-Al₁₂N₁₂. These remarkable outcomes promote transition-metal-atom-doped Al₁₂N₁₂ nanocages as potential applicants for the design of high-performance NLO materials.

中文翻译：

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过渡金属掺杂：一种新的有效方法，可在氮化铝纳米笼中显着提高非线性光学响应†

在Al ₁₂ N ₁₂纳米笼上进行了第一行过渡金属原子（M）的外表面掺杂，以评估掺杂材料的几何，热力学，电子和非线性光学性质。将过渡金属掺杂在Al ₁₂ N ₁₂纳米笼的不同位置上，得到M @ x-Al ₁₂ N ₁₂（其中M = Sc，Ti，V，Cr，Mn，Fe，Co，Ni，Cu，Zn和x = b ₆₄，b ₆₆，r ₆和r ₄）。掺杂的纳米笼中携带的过渡金属原子位于Al–N键上（b ₆₄ / b ₆₆位）或六个以上（r ₆）和四元环（r ₄）。旋转极化DFT研究表明，对于Mn @ x-Al ₁₂ N _12而言，最稳定的自旋单调增加至六重峰，然后对于Zn @ x-Al ₁₂ N ₁₂逐渐降低至单重峰。过渡金属原子化学吸附在Al ₁₂ N ₁₂纳米笼上，这从非常高的结合焓（-16至-64 kcal mol ^-1）。分析了NBO电荷和键序，以使过渡金属和纳米笼之间的键合强度和性质合理化。结果发现，无论掺杂位置和原子序数如何，过渡金属原子都可以显着降低HOMO-LUMO间隙（E _H-L），最多可降低纯Al ₁₂ N _12的40％。通过将远程分离方法中，第一超极化率（β ₀）进行了计算值。过渡金属掺杂的纳米笼的NLO响应与其碱金属掺杂的类似物的NLO响应相当，这是非常显着的，因为碱金属原子是NLO响应的最佳诱导剂之一。最好NLO响应（β ₀Cu @ r ₆ -Al ₁₂ N _12的计算结果为1.85×10 ⁴ au）。这些非凡的成果促进了过渡金属原子掺杂的Al ₁₂ N ₁₂纳米笼的发展，成为设计高性能NLO材料的潜在申请人。