In many tetrahedral network-forming liquids, structural relaxation is anomalously accelerated by compression over relatively low pressure ranges. Here, for silica, we study this problem through comparative molecular dynamics simulations using two different models. Under compression, the network structures are compacted by slight tuning of the intertetrahedral bond angles while nearly preserving the unit tetrahedral structure. The consequent structural changes are remarkable for length scales larger than the nearest neighbor ion-pair distances. Accompanying with such structural changes, the interactions of the nearest Si-O pairs remain almost unchanged, whereas those of other ion pairs are, on average, strengthened by the degree of compression. In particular, the enhancement of the net Si-O interactions at the next nearest neighbor distance, which assist an ion in escaping from the potential well, reduces the activation energy, leading to a significant acceleration of structural relaxation. The results of our comparative molecular dynamics simulations are compatible with the scenario proposed by Angell, and further indicate that the structural relaxation dynamics cannot be uniquely determined by the configurations but strongly depends on the details of the coupling between the structure and the interaction.

中文翻译：

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液态二氧化硅结构弛豫时间的负密度依赖性：来自比较分子动力学研究的见解

在许多形成四面体网络的液体中，结构松弛通过在相对低压范围内的压缩而异常加速。在这里，对于二氧化硅，我们通过使用两种不同模型的比较分子动力学模拟来研究这个问题。在压缩下，网络结构通过略微调整四面体键角而被压实，同时几乎保留了单位四面体结构。对于大于最近邻离子对距离的长度尺度，随之而来的结构变化是显着的。伴随着这种结构变化，最近的 Si-O 对的相互作用几乎保持不变，而其他离子对的相互作用平均而言会因压缩程度而增强。特别是，在下一个最近邻距离处的净 Si-O 相互作用的增强，这有助于离子从势阱中逃逸，降低了活化能，导致结构弛豫的显着加速。我们的比较分子动力学模拟的结果与 Angell 提出的方案兼容，并进一步表明结构弛豫动力学不能由构型唯一确定，而在很大程度上取决于结构和相互作用之间耦合的细节。