Density-optimized radial exponents for X-ray charge-density refinement from ab initio crystal calculations.
Density-optimized radial exponents for X-ray charge-density refinement from ab initio crystal calculations.
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从头开始晶体计算的 X 射线电荷密度细化的密度优化径向指数。
DOI：
10.1107/s0108767300018547
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
P. Coppens
中科院分区：
文献类型：
--
作者：
A. Volkov;Y. Abramov;P. Coppens
利用基于周期密度泛函(DFT)计算的25个分子晶体的结构因子，对Hansen-Coppens多极模型的kappa和kappa伸缩参数精确值的变化趋势进行了评估。正如以前发现的和物理上预期的那样，球价壳卡帕参数与原子净电荷密切相关，负原子被扩展，反之亦然。Kappa参数衡量了非球形变形函数的径向相关性，对于特定的键合环境是非常一致的。观察到碳和氧的系统性趋势，但氮的数值变化更大。表中列出了不同成键环境中氧和碳的平均值，当实验数据的精炼因电荷密度参数集缺乏唯一性而受到影响时，可以使用这些平均值。氮气值必须根据特定的键合环境进行更精细的调整。原子电荷和卡帕之间的关系提供了在非常大的分子的电荷密度精化中引入约束的可能性，对此参数集的尺寸的减小可能是必不可少的。
Structure factors based on periodic density-functional (DFT) calculations on 25 molecular crystals have been used to evaluate trends in refined values of the kappa and kappa' expansion-contraction parameters of the Hansen-Coppens multipole formalism. As found previously and expected physically, the spherical-valence-shell kappa parameters are closely related to the net atomic charges, negative atoms being expanded and vice versa. kappa' parameters, which scale the radial dependence of the non-spherical deformation functions, are remarkably consistent for particular bonding environments. Systematic trends are observed for both carbon and oxygen, but the values obtained for nitrogen show a larger variation. Average values for oxygen and carbon in different bonding environments are tabulated and can be used whenever refinement of experimental data is affected by lack of uniqueness of the charge-density parameter set. Values for nitrogen must be more finely tuned to the specific bonding environment. The relation between atomic charge and kappa offers the possibility of introducing a constraint in the charge-density refinement of very large molecules, for which reduction of the size of the parameter set may be essential.