发表机构
Laboratoire Charles Coulomb (L2C), Univ. Montpellier, CNRS（夏尔·库仑实验室（L2C），蒙彼利埃大学，法国国家科学研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过蒙特卡洛模拟和变分方法，揭示了半柔性磁性聚合物中刚度与磁自由度耦合导致的丰富相图，包括一级相变和有序晶体相。
AI 中文摘要
我们研究了一种半柔性磁性聚合物，其中每个单体携带一个二态自旋，从而产生耦合的构象、刚度和磁自由度。该模型为体内核蛋白复合物提供了最小表示，其中必须同时容纳DNA弯曲刚度和桥接蛋白。我们采用面心立方（FCC）晶格上的蒙特卡洛模拟，并辅以变分自由能上界方法，来表征作为弯曲刚度和温度函数的零场相图。在低刚度下，我们识别出一个一级相变，将线圈到球体的塌缩与铁磁到顺磁的转变相结合。在较低温度下，另一个一级相变将无序球体与有序晶体分开，该晶体以键切线的向列类取向序为特征。在高刚度下，球体消失，导致直接的线圈到晶体的一级相变。这些结果展示了链刚度和磁自由度如何与聚合物构象耦合，并重组零场相图。我们的模型连接了柔性磁性聚合物和半柔性均聚物这两个极限情况，后者对应于所有自旋对齐的强场极限。
英文摘要
We study a semiflexible magnetic polymer in which each monomer carries a two-state spin, giving rise to coupled conformational, stiffness, and magnetic degrees of freedom. The model provides a minimal representation of nucleoprotein complexes in vivo, in which DNA bending rigidity and bridging proteins must be simultaneously accommodated. We employ Monte Carlo simulations on a face-centered-cubic (FCC) lattice, complemented by a variational free-energy upper-bound approach, to characterize the zero-field phase diagram as a function of bending stiffness and temperature. At low stiffness, we identify a first-order transition combining coil-to-globule collapse with a ferromagnetic-to-paramagnetic transition. At lower temperatures, an additional first-order transition separates the disordered globule from an ordered crystal characterized by nematic-like orientational order of the bond tangents. At high stiffness, the globule disappears, resulting in a direct first-order coil-to-crystal transition. These results demonstrate how chain stiffness and magnetic degrees of freedom couple to polymer conformation and reorganize the zero-field phase diagram. Our model connects the two limiting cases of flexible magnetic polymers and semiflexible homopolymers, the latter corresponding to the strong-field limit in which all spins are aligned.
Comments15 pages, 16 figures (main+appendices)
