Ramírez González Juan Pedro, Cinacchi Giorgio
Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, E-28049 Madrid, Spain.
Departamento de Física Teórica de la Materia Condensada, Instituto de Física de la Materia Condensada (IFIMAC), Instituto de Ciencias de Materiales "Nicolás Cabrera," Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, E-28049 Madrid, Spain.
J Chem Phys. 2023 Jul 28;159(4). doi: 10.1063/5.0153596.
By mostly using Monte Carlo numerical simulation, this work investigates the densest-known packings and phase behavior of hard spherical capsids, i.e., hard infinitesimally thin spherical caps with a subtended angle larger than the straight angle. The infinitely degenerate densest-known packings are all characterized by hard spherical capsids that interlock and can be subdivided into three families. The first family includes crystalline packings that are constructed by suitably rotating and stacking layers of hexagonally arranged and suitably tilted hard spherical capsids; depending on the successive rotations, the crystalline packings of this family can become the face-centered cubic crystal, the hexagonal close-packed crystal, and their infinitely degenerate variants in the hard-sphere limit. The second family includes crystalline packings that are characterized by rhombic motifs; they all become the face-centered cubic crystal in the hard-sphere limit. The third family includes crystalline packings that are constructed by suitably shifting and stacking layers in which hard spherical capsids are arranged in tightly packed, straight or zigzag, columns; depending on the successive shifts, the crystalline packings of this family can become the face-centered cubic crystal, the hexagonal close-packed crystal, and their infinitely degenerate variants in the hard-sphere limit. In the plane number density vs subtended angle, the phase diagram of hard spherical capsids features a hexagonal columnar liquid-crystalline phase, toward the hard-hemispherical-cap limit, and a plastic-crystalline phase, toward the hard-sphere limit, in addition to the isotropic fluid phase and crystalline phases. On departing from the hard-sphere limit, the increasing propensity of hard spherical capsids to interlock progressively disfavors the plastic-crystalline phase while favoring auto-assemblage into mostly dimeric interlocks in the denser isotropic fluid phase so that a purely entropic isotropic-fluid-plastic-crystal-isotropic-fluid re-entrant sequence of phase transitions is observed in systems of hard spherical capsids with a subtended angle intermediate between the straight angle and the complete angle.
通过主要使用蒙特卡罗数值模拟，本研究调查了硬球形衣壳（即所对角度大于平角的无限薄硬球冠）的已知最密堆积和相行为。所有无限简并的已知最密堆积都以相互连锁的硬球形衣壳为特征，可细分为三个族。第一族包括通过对六边形排列且适当倾斜的硬球形衣壳层进行适当旋转和堆叠而构建的晶体堆积；根据连续旋转情况，该族的晶体堆积在硬球极限下可变为面心立方晶体、六方密堆积晶体及其无限简并变体。第二族包括以菱形图案为特征的晶体堆积；它们在硬球极限下都变为面心立方晶体。第三族包括通过对硬球形衣壳紧密排列成直列或之字形列的层进行适当平移和堆叠而构建的晶体堆积；根据连续平移情况，该族的晶体堆积在硬球极限下可变为面心立方晶体、六方密堆积晶体及其无限简并变体。在平面数密度与所对角度的关系中，硬球形衣壳的相图除了各向同性流体相和晶体相外，在接近硬半球冠极限处有一个六方柱状液晶相，在接近硬球极限处有一个塑性晶体相。从硬球极限出发，硬球形衣壳相互连锁的倾向增加，逐渐不利于塑性晶体相，同时有利于在密度更大的各向同性流体相中自组装成主要为二聚体的连锁结构，因此在所对角度介于平角和周角之间的硬球形衣壳系统中观察到了纯粹由熵驱动的各向同性流体 - 塑性晶体 - 各向同性流体再入相变序列。
