Leetmaa Mikael, Ljungberg Mathias, Ogasawara Hirohito, Odelius Michael, Näslund Lars-Ake, Nilsson Anders, Pettersson Lars G M
Fysikum, AlbaNova, Stockholm University, SE-106 91 Stockholm, Sweden.
J Chem Phys. 2006 Dec 28;125(24):244510. doi: 10.1063/1.2408419.
X-ray absorption (XA) spectra have been computed based on water structures obtained from a recent fit to x-ray and neutron diffraction data using models ranging from symmetrical to asymmetrical local coordination of the water molecules [A. K. Soper, J. Phys.: Condens. Matter 17, S3273 (2005)]. It is found that both the obtained symmetric and asymmetric structural models of water give similar looking XA spectra, which do not match the experiment. The fitted models both contain unphysical structures that are allowed by the diffraction data, where, e.g., hydrogen-hydrogen interactions may occur. A modification to the asymmetric model, in which the non-hydrogen-bonded OH intramolecular distance is allowed to become shorter while the bonded OH distance becomes longer, improves the situation somewhat, but the overall agreement is still unsatisfactory. The electric field (E-field) distributions and infrared (IR) spectra are also calculated using two established theoretical approaches, which, however, show significant discrepancies in their predictions for the asymmetric structural models. Both approaches predict the Raman spectrum of the symmetric model fitted to the diffraction data to be significantly blueshifted compared to experiment. At the moment no water model exists that can equally well describe IR/Raman, x-ray absorption spectroscopy, and diffraction data.
基于从最近使用从水分子的对称到不对称局部配位模型对X射线和中子衍射数据进行拟合得到的水结构，计算了X射线吸收（XA）光谱[A. K. Soper，《物理：凝聚态物质》17，S3273（2005）]。结果发现，所得到的水的对称和不对称结构模型给出的XA光谱看起来相似，但与实验不匹配。拟合模型都包含衍射数据允许的非物理结构，例如可能发生氢-氢相互作用的地方。对不对称模型进行了修改，即允许非氢键合的OH分子内距离变短，而键合的OH距离变长，情况有所改善，但总体一致性仍然不令人满意。还使用两种已确立的理论方法计算了电场（E场）分布和红外（IR）光谱，然而，它们对不对称结构模型的预测存在显著差异。两种方法都预测，与实验相比，拟合到衍射数据的对称模型的拉曼光谱会有明显的蓝移。目前不存在能够同样好地描述红外/拉曼、X射线吸收光谱和衍射数据的水模型。
