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Magnetic analytic bond-order potential for modeling the different phases of Mn at zero Kelvin

机译：磁性分析键序电位，用于模拟零开尔文温度下Mn的不同相

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摘要

It is known that while group Ⅶ 4d Tc and 5d Re have hexagonally close-packed (hcp) ground states, 3d Mn adopts a complex x-phase ground state, exhibiting complex noncollinear magnetic ordering. Density functional theory (DFT) calculations have shown that without magnetism, the x phase is still the ground state of Mn implying that magnetism and the resultant atomic-size difference between large- and small-moment atoms are not the critical factors, as is commonly believed, in driving the anomalous stability of the x phase over hcp. Using a canonical tight-binding (TB) model, it is found that for a more than half-filled d band, while harder potentials stabilize close-packed hcp, a softer potential stabilizes the more open x phase. By analogy with the structural trend from open to close-packed phases down the group Ⅳ elements, the anomalous stability of the x phase in Mn is shown to be due to 3d valent Mn lacking d states in the core which leads to an effectively softer atomic repulsion between the atoms than in 4d Tc and 5d Re. Subsequently, an analytic bond-order potential (BOP) is developed to investigate the structural and magnetic properties of elemental Mn at 0 K. It is derived within BOP theory directly from a new short-ranged orthogonal d-valent TB model of Mn, the parameters of which are fitted to reproduce the DFT binding energy curves of the four experimentally observed phases of Mn, namely, α, β, γ, δ, and ε-Mn. Not only does the BOP reproduce qualitatively the DFT binding energy curves of the five different structure types, it also predicts the complex collinear antiferromagnetic (AFM) ordering in α-Mn, the ferrimagnetic ordering in β-Mn, and the AFM ordering in γ-, δ-, and ε-Mn that are found by DFT. A BOP expansion including 14 moments is sufficiently converged to reproduce most of the properties of the TB model with the exception of the elastic shear constants, which require further moments. The current TB model, however, predicts values of the shear moduli and the vacancy formation energies that are approximately a factor of 2 too small, so that a future more realistic model for MD simulations will require these properties to be included from the outset in the fitting database.
机译：众所周知，while 4d Tc和5d Re组具有六方密堆积（hcp）基态，而3d Mn采用复杂的x相基态，表现出复杂的非共线磁性排序。密度泛函理论（DFT）计算表明，没有磁性，x相仍然是Mn的基态，这表明磁性以及由此产生的大，小矩原子之间的原子大小差异并不是关键因素，通常据信，在驱动hcp上x相的异常稳定性方面。使用规范的紧束缚（TB）模型，发现对于超过一半填充的d带，较硬的电位稳定了密堆积的hcp，而较软的电位则稳定了更开放的x相。与从Ⅳ族元素到开放相到密堆积相的结构趋势类似，Mn中x相的异常稳定性被证明是由于核中3d价Mn缺乏d状态，从而导致了原子更有效的软化。原子之间的排斥力比4d Tc和5d Re中的原子强。随后，开发了一种分析键序势（BOP）来研究元素K在0 K时的结构和磁性。它是在BOP理论内直接从新的锰的短距离正交d价TB模型推导而来的。拟合其参数以再现Mn的四个实验观察到的相的DFT结合能曲线，即α，β，γ，δ和ε-Mn。 BOP不仅定性地重现了五种不同结构类型的DFT结合能曲线，而且还预测了α-Mn中的复杂共线反铁磁（AFM）有序，β-Mn中的亚铁磁有序以及γ-中AFM的有序性DFT发现的δ-和ε-Mn。包括14个弯矩的BOP扩展已充分收敛，可以再现TB模型的大多数特性，但弹性剪切常数除外，这需要更多弯矩。但是，当前的TB模型预测的剪切模量值和空位形成能的值大约是2的因数太小，因此，对于MD仿真的未来更现实的模型将要求从一开始就将这些特性包括在内。拟合数据库。

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