PageRankベース集団変数に沿ったアンブレラサンプリングにより解明されたCALF-20の水和誘起構造転換のメカニズム

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🔬研究者:MOFの水和安定性と構造転換を自由エネルギー地形で捉える計算手法に関心のある材料科学・CCUS研究者に有用。

🏢実務担当者:CO2回収設備の吸着材選定や耐久性評価に関わる技術者にとって、水和劣化メカニズムの基礎的示唆となる。

Computational understanding of the structural transformation of superstable adsorbents for carbon capture and sequestration represents a forefront scientific endeavor. It enables not only a fundamental understanding of these processes but also the application of the acquired knowledge to the crystal engineering of novel, more efficient materials for industrial applications. Herein, hydration-induced structural transformations in CALF-20 were investigated using ab initio molecular dynamics, umbrella sampling, and a graph-theoretical collective variable based on the PageRank (PR) algorithm. The study was motivated by the recent experimental identification of the hydrated τ- and γ-CALF-20 polymorphs derived from the α phase. Conventional NVT simulations at T = 353 K revealed only weak and transient interactions between water molecules and Zn2+ coordination centers, indicating that hydration events occur on time scales inaccessible to unbiased simulations. To capture these rare events, atomic configurations were represented as weighted interaction networks and analyzed using the PageRank formalism. The resulting PR collective variable enabled reconstruction of the free-energy landscape associated with water coordination and framework reorganization. Distinct free-energy minima were identified and correlated with Zn2+–Ow distances in excellent agreement with experimental values reported for the τ- and γ-phases. Structural analysis revealed a transformation from a pentacoordinated Zn2+ environment in the α phase to hydrated hexacoordinated intermediates stabilized by Zn2+–water interactions. At larger PR values, excessive water coordination induced oxalate detachment and formation of a distorted tetracoordinated structure. These results demonstrate that hydration-induced phase transformations in CALF-20 arise from cooperative reorganization of the entire coordination network and establish PageRank as a promising collective variable for enhanced sampling of flexible metal–organic frameworks.

• semanticscholar https://pubs.acs.org/jpccck/article-pdf/doi/10.1021/acs.jpcc.6c04407/68452925/acs.jpcc.6c04407.pdffirst seen 2026-09-12 05:33:54 · last seen 2026-09-22 05:05:59