D'Angelo Paola, Roscioni Otello Maria, Chillemi Giovanni, Della Longa Stefano, Benfatto Maurizio
Dipartimento di Chimica, Università di Roma La Sapienza, Piazzale A. Moro 5, 00185 Rome, Italy.
J Am Chem Soc. 2006 Feb 15;128(6):1853-8. doi: 10.1021/ja0562503.
A general procedure to compute X-ray absorption near-edge structure (XANES) spectra within multiple-scattering theory starting from molecular dynamics (MD) structural data has been developed and applied to the study of a Ni(2+) aqueous solution. This method allows one to perform a quantitative analysis of the XANES spectra of disordered systems using a proper description of the thermal and structural fluctuations. The XANES spectrum of Ni(2+) in aqueous solution has been calculated using the structural information obtained from the MD simulations without carrying out any minimization in the structural parameter space. A very good reproduction of the experimental data was obtained including the second-shell water molecules in the calculation, thus showing that the second hydration shell provides a detectable contribution to the XANES spectra of ionic solutions. The analysis including the first-shell cluster only permitted us to quantitatively determine the effect of disorder on the amplitude of the XANES spectra for molecular complexes. These results simultaneously confirm the reliability of the procedure and the structural results obtained from MD simulations. The combination of MD and XANES is found to be very helpful to get important new insights into the quantitative estimation of structural properties of disordered systems.
一种从分子动力学（MD）结构数据出发，基于多重散射理论计算X射线吸收近边结构（XANES）光谱的通用程序已被开发出来，并应用于对Ni(2+)水溶液的研究。该方法允许使用对热涨落和结构涨落的适当描述，对无序体系的XANES光谱进行定量分析。利用从MD模拟获得的结构信息，在不进行结构参数空间最小化的情况下，计算了Ni(2+)在水溶液中的XANES光谱。计算中包含了第二壳层水分子，从而很好地再现了实验数据，这表明第二水合壳层对离子溶液的XANES光谱有可检测的贡献。仅包含第一壳层簇的分析使我们能够定量确定无序对分子络合物XANES光谱振幅的影响。这些结果同时证实了该程序的可靠性以及从MD模拟获得的结构结果的可靠性。发现MD和XANES的结合对于深入了解无序体系结构性质的定量估计非常有帮助。
