阳离子掺杂的LiMnO $_{2}$的相稳定性]{在GGA +U近似下阳离子掺杂的LiMnO $_{2}$的相稳定性
Phase stability of cation-doped LiMnO$_{2}$]{Phase stability of cation-doped LiMnO$_{2}$ within the GGA+U approximation
摘要：
对锂离子电池的候选阴极材料LiMn $_{1-x}$ M $_x$ O $_{2}$（其中（$x=0.25$，M=Ni，Fe，Co，Mg））进行GGA+U近似内的第一原理密度泛函理论计算，以研究掺杂对单斜结构相对于层状菱面体结构的不稳定性的影响。这项工作的主要动机是确定在何种程度上的预测电子更现实的GGA+U治疗将不同于GGA内获得的。发现了一些显著的质的变化：对于菱形结构的原始体系，Mn离子在GGA+U中表现出高自旋态，而不是GGA中的低自旋（金属）态。掺杂的菱面体结构在GGA+U中是不稳定的，而不是像在GGA中那样是亚稳定的。在单斜结构中，GGA+U和GGA中的掺杂剂氧化态相同（三价Fe，二价Co，Ni）。Co和Ni离子在GGA+U中的自旋态比在GGA中的自旋态高。二价掺杂剂在GGA+U内比三价掺杂剂更大程度上使单斜结构不稳定，如从先前GGA计算所预期。总的来说，我们的研究结果表明，GGA和GGA+U中计算的性质之间的相对接近的协议有时可能是误导，因为潜在的电子行为可能是深刻的不同。
英文摘要：
First principles density functional theory calculations within the GGA+U approximation were performed for LiMn$_{1-x}$M$_x$O$_{2}$, a candidate cathode material for lithium-ion batteries, with ($x=0.25$, M=Ni, Fe, Co, Mg), to investigate the effect of doping on the destabilization of the monoclinic structure relative to the layered rhombohedral structure. A primary motivation of this work was to determine to what extent the predictions of the electronically more realistic GGA+U treatment would differ from those obtained within the GGA. Several significant qualitative changes are found. For the pristine system in the rhombohedral structure, Mn ions show a high-spin state within GGA+U, rather than the low spin (metallic) state found in GGA. The doped rhombohedral structure is unstable within GGA+U, rather than metastable, as in GGA. In the monoclinic structure, the dopant oxidation states are the same (trivalent Fe, divalent Co, Ni) in GGA+U and GGA. Co and Ni ions show a higher spin state in GGA+U than in GGA. The divalent dopants destabilized the monoclinic structure to a greater extent than trivalent dopants within the GGA+U, as expected from previous GGA calculations. Overall, our results suggest that the relatively close agreement sometimes found between properties calculated within the GGA and GGA+U may be misleading, because the underlying electronic behaviors may be profoundly different.
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