Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
J Phys Condens Matter. 2011 Oct 12;23(40):405403. doi: 10.1088/0953-8984/23/40/405403. Epub 2011 Sep 22.
We have performed a set of first-principles simulations to consider the possible phase transitions in molecular crystals of HCN under high pressure. Our calculations reveal several transition paths from the orthorhombic phase to tetragonal and then to triclinic phases. The transitions from the orthorhombic to the tetragonal phases are of the second order, whereas those from the tetragonal to the triclinic phases turn out to be of the first-order type and characterized by an abrupt decrease in volume. Our calculations show that, by adjustment of the temperature and pressure of the HCN molecular crystal, novel layered and polymeric crystals with insulating, semiconducting or metallic properties can be found. Based on our simulation results, two different crystal formation mechanisms are deduced. The stabilities of the predicted structures at ambient pressure are further assessed by performing phonon or MD simulations. In addition, the electron transport properties of the predicted polymers are obtained using the non-equilibrium Green's function technique combined with density functional theory. The results show that the polymers have metallic-like I-V characteristics.
我们进行了一系列第一性原理模拟，以研究高压下 HCN 分子晶体中可能发生的相变。我们的计算揭示了从正交相到四方相再到三斜相的几种转变路径。从正交相到四方相的转变是二级相变，而从四方相到三斜相的转变则是一级相变，表现为体积的急剧下降。我们的计算表明，通过调整 HCN 分子晶体的温度和压力，可以发现具有绝缘、半导体或金属性质的新型层状和聚合晶体。基于我们的模拟结果，推导出了两种不同的晶体形成机制。通过声子或 MD 模拟进一步评估了预测结构在常压下的稳定性。此外，使用非平衡格林函数技术结合密度泛函理论获得了预测聚合物的电子输运性质。结果表明，聚合物具有类金属的 I-V 特性。
