The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values for the range of the potential, with the aim of investigating the conditions under which a diamond crystal can be formed. We find that the diamond phase is never stable for our longer-ranged potential. At low temperatures and pressures, the fluid freezes into a body-centred-cubic solid that can be viewed as two interpenetrating diamond lattices with a weak interaction between the two sublattices. Upon compression, an orientationally ordered face-centred-cubic crystal becomes more stable than the body-centred-cubic crystal, and at higher temperatures a plastic face-centered-cubic phase is stabilized by the increased entropy due to orientational disorder. A similar phase diagram is found for the shorter-ranged potential, but at low temperatures and pressures, we also find a region over which the diamond phase is thermodynamically favored over the body-centred-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centred-cubic solid explains why it is stable even though the enthalpy of the latter phase is lower. Some preliminary studies on the growth of the diamond structure starting from a crystal seed were performed. Even though the diamond phase is never thermodynamically stable for the longer-ranged model, direct coexistence simulations of the interface between the fluid and the body-centred-cubic crystal and between the fluid and the diamond crystal show that, at sufficiently low pressures, it is quite probable that in both cases the solid grows into a diamond crystal, albeit involving some defects. These results highlight the importance of kinetic effects in the formation of diamond crystals in systems of patchy particles.
From layered 2D carbon to 3D tetrahedral original allotropes C12 and C18 with physical properties related to diamond: Crystal chemistry and DFT investigations
Silicon Driven Facet Regulation Enables Tunable Micro-Diamond Architectures in Liquid Ga In
University of Aveiro（阿威罗大学）；Intelligent Systems Associate Laboratory (LASI)（智能系统联合实验室）；Instituto de Engenharia de Sistemas e Computadores - Microssistemas e Nanotecnologia（系统工程与计算机研究所-微系统与纳米技术）；IPFN, Instituto Superior Técnico, University of Lisbon（里斯本理工大学高级理工学院核物理研究组）；DECN, Instituto Superior Técnico, University of Lisbon（里斯本理工大学高级理工学院能源转换中心）
Electronic structure of the frustrated diamond lattice magnet NiRh$_2$O$_4$
$A$位尖晶石NiRh $_2$ O $_4$是自旋为1的金刚石晶格磁体的唯一已知实现，并且被预测为由受抑最近邻和次最近邻交换以及轨道简并驱动的非常规磁性现象。以前的工作没有发现磁秩序的迹象，但发现了一个缺口色散磁激发表明可能的价键磁基态。然而，许多竞争的低能量自由度和有限的经验微观约束的存在使进一步的分析复杂化。在这里，我们进行共振非弹性X射线散射（RIXS）和X射线吸收光谱（XAS）来表征的局部电子结构的NiRh $_2$ O $_4$。的RIXS数据可以部分地描述由四面体配位的镍$^{2+}$的单离子模型，并表示一个tetrandom畸变$Δt_2\!=\!70$毫电子伏，分裂的$t_2$轨道成一个高能量的轨道单线态和较低能量的轨道双峰。我们确定的RIXS光谱的特点是一致的铑-镍两个网站的激发表明强金属-金属杂化介导的氧在NiRh $_2$ O $_4$。我们还确定了电子-声子耦合的签名，通过外观的声子边带，衣服的晶体场激发。这些结果建立了NiRh $_2$ O $_4$的磁性相关的关键能量尺度，并进一步表明，共价性和晶格动力学在控制$A$位尖晶石的磁性基态中起着至关重要的作用。
