自旋交叉配合物Fe(pap-5NO2)2中 barocaloric效应的振动起源：DFT与平均场结合研究
Vibrational Origin of the Barocaloric Effect in the Spin-Crossover Complex Fe(pap-5NO2)2: A Combined DFT and Mean-Field Study
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中文总结 AI 辅助
本研究结合DFT与平均场理论，明确自旋交叉配合物Fe(pap-5NO2)2的barocaloric效应主要源于金属-配体振动贡献，定量重现实验结果并确定其熵变机制。
中文摘要 AI 辅助
尽管近期已报道了自旋交叉配合物Fe(pap-5NO2)2的 barocaloric性能，但其压力诱导熵变的微观起源仍知之甚少。特别是，振动、构型和自旋自由度对 barocaloric响应的相对贡献尚未得到定量确定。本文中，我们开发了一个结合密度泛函理论（DFT）计算与有效平均场哈密顿量的理论框架，以研究该自旋交叉配合物的 barocaloric效应。将第一性原理计算得到的低自旋（S = 0）和高自旋（S = 2）态的振动频率纳入热力学模型，该模型明确考虑了构型、自旋和晶格熵的贡献。通过位移矢量重叠分析建立两种自旋态振动光谱的对应关系，我们确定低频和中频金属-配体振动是振动熵变的主要微观起源。所提出的模型定量重现了实验报道的2 kbar压力变化下的 barocaloric熵变，对应最大可逆熵变约为70 J kg-1 K-1，且预测的常压下自旋交叉温度T_1/2 = 313 K，与实验值308 K吻合良好。熵组分分析显示，与分子振动相关的晶格熵约占总 barocaloric响应的84%，而构型和自旋贡献相对较小。
英文摘要
Despite the barocaloric performance recently reported for the spin-crossover complex Fe(pap-5NO2)2, the microscopic origin of its pressure-induced entropy change remains poorly understood. In particular, the relative contributions of vibrational, configurational, and spin degrees of freedom to the barocaloric response have not yet been quantitatively established. Here, we develop a theoretical framework that combines density functional theory (DFT) calculations with an effective mean field Hamiltonian to investigate the barocaloric effect in this spin-crossover complex. Vibrational frequencies of the low-spin (S = 0) and high-spin (S = 2) states obtained from first-principles calculations are incorporated into a thermodynamic model that explicitly accounts for configurational, spin, and lattice entropy contributions. By establishing a correspondence between the vibrational spectra of both spin states through displacement-vector overlap analysis, we identify low and mid frequency metal-ligand vibrations as the primary microscopic origin of the vibrational entropy change. The proposed model quantitatively reproduces the experimentally reported barocaloric entropy change for a pressure variation of 2 kbar, corresponding to a maximum reversible entropy change of approximately 70 J kg-1 K-1, and predicts a spin-crossover temperature of T_1/2 = 313 K under ambient pressure, in excellent agreement with the experimental value of 308 K. Analysis of the entropy components reveals that lattice entropy associated with molecular vibrations accounts for approximately 84% of the total barocaloric response, whereas configurational and spin contributions are comparatively small.
发表机构
- Universidade do Estado do Rio de Janeiro（里约热内卢州立大学）
- Oak Ridge National Laboratory（橡树岭国家实验室）
- Universidade Federal Fluminense（弗鲁米嫩塞联邦大学）
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