Chachiyo Teepanis, Rodriguez Jorge H
Department of Physics, Purdue University, West Lafayette, Indiana 47907-2036, USA.
J Chem Phys. 2005 Sep 1;123(9):94711. doi: 10.1063/1.2007708.
An efficient computational method for locating minimum-energy crossing points (MECPs) between potential-energy surfaces in spin-crossover transitions and nonadiabatic spin-forbidden (bio)chemical reactions is introduced. The method has been tested on the phenyl cation and the computed MECP associated with its radiationless singlet-triplet spin crossover is in good agreement with available data. However, the convergence behavior of the present method is significantly more efficient than some alternative methods which allows us to study nonadiabatic processes in larger systems such as spin crossover in metal-containing compounds. The convergence rate of the method obeys a fast logarithmic law which has been verified on the phenyl cation. As an application of this new methodology, the MECPs of the ferrous complex Fe(ptz)(6)(2), which exhibits light-induced excited spin state trapping, have been computed to identify their geometric and energetic parameters during spin crossover. Our calculations, in conjunction with spin-unrestricted density-functional calculations, show that the transition from the singlet ground state to a triplet intermediate and to the quintet metastable state of Fe(ptz)(6)(2) is accompanied by unusually large bond-length elongations of the axial ligands ( approximately 0.26 and 0.23 A, respectively). Our results are consistent with crystallographic data available for the metastable quintet but also predict new structural and energetic information about the triplet intermediate and at the MECPs which is currently not available from experiment.
介绍了一种用于确定自旋交叉跃迁和非绝热自旋禁阻（生物）化学反应中势能面之间最小能量交叉点（MECP）的高效计算方法。该方法已在苯基阳离子上进行了测试，计算得到的与其无辐射单重态 - 三重态自旋交叉相关的MECP与现有数据吻合良好。然而，本方法的收敛行为比一些替代方法显著更高效，这使我们能够研究更大体系中的非绝热过程，如含金属化合物中的自旋交叉。该方法的收敛速率服从快速对数规律，这已在苯基阳离子上得到验证。作为这种新方法的应用，已计算出表现出光诱导激发自旋态捕获的亚铁配合物Fe(ptz)(6)(2)的MECP，以确定其在自旋交叉过程中的几何和能量参数。我们的计算与自旋非限制密度泛函计算相结合表明，Fe(ptz)(6)(2)从单重态基态到三重态中间体再到五重态亚稳态的转变伴随着轴向配体的键长异常大幅伸长（分别约为0.26和0.23 Å）。我们的结果与亚稳态五重态的晶体学数据一致，但也预测了关于三重态中间体和MECP的新结构和能量信息，目前这些信息无法从实验中获得。
