发表机构
The University of Osaka; Massachusetts Institute of Technology（大阪大学; 麻省理工学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出双态化学势积分（TSCPI）方法，高效计算活化自由能，揭示移动间隙原子对缺陷动力学具有阻滞与加速双重作用，并阐明其随浓度变化的交叉机制。
AI 中文摘要
移动间隙原子在缺陷迁移过程中发生再分布，这使得缺陷动力学的预测变得复杂，并导致了关于加速和阻滞效应的相互矛盾的报道。我们在固定间隙原子化学势的正则系综中构建了缺陷活化模型，并定义了路径自由能景观 $\Delta G(\Lambda;T,\mu)$ 及相应的活化自由能 $\Delta G^{\ddagger}$。我们通过两种方法计算这些量：基于平均力关系的超平面约束热力学积分，以及双态化学势积分（记为TSCPI）。后者仅需对初始态和过渡态进行采样；一次化学势积分即可在宽 $\mu$ 范围内得到 $\Delta G^{\ddagger}(T,\mu)$，从而能够快速绘制温度和化学势的图谱。将该方法应用于FCC、BCC和HCP金属中氢（包括Zr中的面内和面外扩散）以及BCC W中氦的空位扩散，两种自由能路径得到的结果与分子动力学均方位移得到的扩散系数一致。所得图谱揭示了抑制和增强的区域，包括随氢浓度增加从抑制到增强的交叉转变。位点占据分析将势垒变化与态相关的位点谱变化和可转移的间隙原子相互作用项联系起来。
英文摘要
Mobile interstitial atoms redistribute while defects migrate, complicating prediction of defect kinetics and leading to contradictory reports of acceleration and retardation. We formulate defect activation in a grand-canonical ensemble at fixed interstitial chemical potential and define a pathway free-energy landscape $ΔG(Λ;T,μ)$ and the corresponding activation free energy $ΔG^{\ddagger}$. We compute these quantities using both hyperplane-constrained thermodynamic integration via a mean force relation and a two-state chemical-potential integration, denoted TSCPI. The latter requires sampling only the initial and transition states; a single chemical-potential integration then yields $ΔG^{\ddagger}(T,μ)$ across a wide $μ$ range, enabling rapid mapping over temperature and chemical potential. Applied to vacancy diffusion in FCC, BCC, and HCP metals with H (including in plane and cross plane diffusion in Zr) and in BCC W with He, both free energy routes agree with diffusion coefficients from molecular dynamics mean square displacements. The resulting maps reveal regimes of suppression and enhancement, including a crossover from suppression to enhancement with increasing hydrogen concentration. A site occupancy analysis links barrier shifts to state dependent site spectrum changes and transferable interstitial interaction terms.
