Munshi Parthapratim, Madsen Anders Ø, Spackman Mark A, Larsen Sine, Destro Riccardo
University of Western Australia, Australia.
Acta Crystallogr A. 2008 Jul;64(Pt 4):465-75. doi: 10.1107/S010876730801341X. Epub 2008 Jun 17.
Anisotropic displacement parameters (ADPs) are compared for H atoms estimated using three recently described procedures, both among themselves and with neutron diffraction results. The results convincingly demonstrate that all methods are capable of giving excellent results for several benchmark systems and identify systematic discrepancies for several atom types. A revised and extended library of internal H-atom mean-square displacements is presented for use with Madsen's SHADE web server [J. Appl. Cryst. (2006), 39, 757-758; http://shade.ki.ku.dk], and the improvement over the original SHADE results is substantial, suggesting that this is now the most readily and widely applicable of the three approximate procedures. Using this new library--SHADE2--it is shown that, in line with expectations, a segmented rigid-body description of the heavy atoms yields only a small improvement in the agreement with neutron results. The SHADE2 library, now incorporated in the SHADE web server, is recommended as a routine procedure for deriving estimates of H-atom ADPs suitable for use in charge-density studies on molecular crystals, and its widespread use should reveal remaining deficiencies and perhaps overcome the inherent bias in the majority of such studies.
使用最近描述的三种方法对氢原子的各向异性位移参数（ADPs）进行了比较，包括这些方法之间的比较以及与中子衍射结果的比较。结果令人信服地表明，所有方法对于几个基准体系都能够给出出色的结果，并且识别出了几种原子类型的系统偏差。本文给出了一个经过修订和扩展的内部氢原子均方位移库，用于与Madsen的SHADE网络服务器配合使用[《应用晶体学杂志》（2006年），39卷，757 - 758页；http://shade.ki.ku.dk]，与原始的SHADE结果相比有显著改进，这表明这是目前三种近似方法中最易于使用且应用最广泛的方法。使用这个新库——SHADE2——结果表明，正如预期的那样，对重原子采用分段刚体描述，与中子结果的一致性仅有小幅改善。现在已纳入SHADE网络服务器的SHADE2库，被推荐作为一种常规方法，用于推导适用于分子晶体电荷密度研究的氢原子ADPs估计值，其广泛应用应能揭示剩余的不足，并可能克服大多数此类研究中固有的偏差。
