Well-tempered metadynamics simulations are employed to explore the phase diagram of ZIF-4, a porous crystalline metal–organic framework of industrial relevance. Despite the vast amount of experimental efforts, the phase diagram that includes ZIF-4 and its related polymorphs has not yet been fully determined. For example, the crystalline phase called ZIF-4-cp is not experimentally observed when high pressure ramps are applied, even though it is known to be stable under temperature and pressure conditions within the studied range. Our simulations shed light on the phase diagram topology and allow us to further look into the collective degrees of freedom that drive the phase transitions in the T = 150–450 K and P = 0–200 MPa region. The porous ZIF-4 phase transforms into ZIF-4-cp through pore closure, while the latter has a phase transition in higher pressure regimes to ZIF-4-cp-II, a transformation which involves subtle changes in the orientation of four member rings with respect to unit cell vectors.

中文翻译：

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来自计算机模拟的 ZIF-4 相图


采用 Well-tempered 元动力学模拟来探索 ZIF-4 的相图，ZIF-4 是一种具有工业相关性的多孔结晶金属-有机框架。尽管进行了大量实验工作，但包括 ZIF-4 及其相关多晶型物的相图尚未完全确定。例如，当施加高压斜坡时，实验不会观察到称为 ZIF-4-cp 的结晶相，即使已知它在研究范围内的温度和压力条件下是稳定的。我们的仿真阐明了相图拓扑结构，并使我们能够进一步研究驱动 T = 150–450 K 和 P = 0–200 MPa 区域相变的集体自由度。多孔 ZIF-4 相通过孔隙闭合转化为 ZIF-4-cp，而后者在较高压力状态下发生相变为 ZIF-4-cp-II，这种转变涉及四个元环相对于晶胞向量方向的细微变化。