非晶态SiN的原子结构：结合Car-Parrinello和Born-Oppenheimer第一性原理分子动力学
Atomic structure of amorphous SiN: combining Car-Parrinello and Born-Oppenheimer first-principles molecular dynamics
摘要：
采用第一性原理分子动力学描述了非晶SiN的原子结构，非化学计量的化合物属于Si $_x$ N $_{y}$家族。为了通过液体的冷却来产生非晶态，利用Car-Parrinello和Born-Oppenheimer方法来获得具有相当大的原子迁移率的系统。在高温下，由于SiN的特殊电子结构，表现出间隙闭合效应，不能遵循Car-Parrinello方法，因为涉及离子和电子自由度的非绝热效应确实发生。通过采用Born-Oppenheimer方法克服了这个缺点，该方法允许在$T$ = 2500 K下实现显著的离子扩散。从这个高扩散的样品，在室温下的非晶状态，得到淬火速率为10 K/ps。创建了四种不同的模型，它们的大小和热循环不同。我们发现，原子N的子网具有与化学计量材料Si $_3$ N $_4$中相同的环境，因为N主要与Si三重配位。还可以发现Si原子与四个N原子配位，如在Si $_3$ N $_4$中，但是它们中的相当大一部分与一个、两个、三个甚至四个Si形成同极键。我们的结果与文献中已有的模型没有太大的不同，但它们具有更高的统计精度，并且更精确地将室温作为分析非晶态结构的参考温度条件。
英文摘要：
First-principles molecular dynamics is employed to describe the atomic structure of amorphous SiN, a non-stoichiometric compound belonging to the Si$_x$N$_{y}$ family. To produce the amorphous state via the cooling of the liquid, both the Car-Parrinello and the Born-Oppenheimer approaches are exploited to obtain a system featuring sizeable atomic mobility. At high temperatures, due to the peculiar electronic structure of SiN, exhibiting gap closing effects, the Car-Parrinello methodology could not be followed since non-adiabatic effects involving the ionic and electronic degrees of freedom do occur. This shortcoming was surmounted by resorting to the Born-Oppenheimer approach allowing to achieve significant ionic diffusion at $T$= 2500 K. From this highly diffusive sample, an amorphous state at room temperature was obtained with a quenching rate of 10 K/ps. Four different models were created, differing by their sizes and the thermal cycles. We found that the subnetwork of atoms N has the same environment than in the stoichiometric material Si$_3$N$_4$ since N is mostly threefold coordinated with Si. Si atoms can also be found coordinated to four N atoms as in Si$_3$N$_4$, but a substantial fraction of them forms homopolar bonds with one, two, three and even four Si. Our results are not too dissimilar from former models available in the litterature but they feature a higher statistical accuracy and refer more precisely to room temperature as the reference thermodynamical condition for the analysis of the structure in the amorphous state.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
