In this work, we describe the thermodynamics and mechanism of CO₂ polymorphic transitions under pressure from form I to form III combining standard molecular dynamics, well-tempered metadynamics, and committor analysis. We find that the phase transformation takes place through a concerted rearrangement of CO₂ molecules, which unfolds via an anisotropic expansion of the CO₂ supercell. Furthermore, at high pressures, we find that defected form I configurations are thermodynamically more stable with respect to form I without structural defects. Our computational approach shows the capability of simultaneously providing an extensive sampling of the configurational space, estimates of the thermodynamic stability, and a suitable description of a complex, collective polymorphic transition mechanism.

中文翻译：

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压力下CO ₂填充多态性：I-III多态性转变的机理和热力学

在这项工作中，我们描述了从标准I到标准I到标准III的压力下CO ₂多晶型转变的热力学和机理，结合了标准的分子动力学，良好的变元动力学和贡献者分析。我们发现，相变是通过协调一致的CO ₂分子重排而发生的，CO ₂分子通过CO ₂的各向异性膨胀而展开超级单元。此外，在高压下，我们发现有缺陷的I型构型相对于没有结构缺陷的I型在热力学上更稳定。我们的计算方法显示了能够同时提供构型空间的大量采样，热力学稳定性的估计以及对复杂的集体多晶型转变机制的适当描述的能力。