Comment on On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model by Volkov, King, Coppens & Farrugia (2006).
Comment on On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model by Volkov, King, Coppens & Farrugia (2006).
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Volkov、King、Coppens 评《论从非球面赝原子模型计算静电势、电场和电场梯度》
DOI：
10.1107/s0108767307001298
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
M. Spackman
中科院分区：
文献类型：
--
作者：
M. Spackman
从非球面伪原子模型中确定相关的物理性质，并与独立的实验和/或计算结果进行比较，仍然是许多基于高分辨率低温x射线衍射数据的现代电荷密度研究的关键目标。最近由Volkov， King， Coppens & Farrugia [Acta crystal]发表的论文。（2006）， A62, 400-408]（以下简称VKCF）代表了在常规电荷密度分析中实现这一目标的重要一步。从非球面伪原子模型出发，提出了新的和改进的计算静电势（ESP）、电场（EF）和电场梯度（EFG）的公式，并将其应用于结构因子的实验集和模型集。具有相当实际意义的是，这些表达式已被纳入到XDPROP的新版本中，XDPROP是XD包的一部分，目前正在广泛使用（Koritsanszky等人，2003）。这封信的目的是补充VKCF所描述的工作，为该工作中提出的一些问题提供更广泛的视角，并对他们提出的一些结果进行评论。VKCF写道（第401页），“从x射线衍射数据计算ESP的各种方法已经被描述并因此在文献中得到应用。这些方法基本上可以分为两种截然不同的方法：(i)直接从实验测量的结构因素（Bertaut, 1978; Schwarzenbach & Thong, 1979; Stewart, 1979）和（ii）从电子密度的静态模型。重要的是要认识到(i)组并不局限于实验测量，而且可以更广泛地应用于任何一组有效的结构因素（例如静态，从非球面伪原子模型计算，如下所述）。此外，方法(i)和方法（ii）之间存在密切关系，并且通过两种方法的组合最有利地计算晶体中的许多性质。几十年前，RF Stewart就从x射线衍射数据中明确地概述了ESP， EF和EFG的这一方面，VKCF引用了Stewart的论文，讨论了从x射线衍射数据中确定“内部矩”（即涉及负r次方的平均值，而不是涉及零和正r次方的“外部矩”，如偶极子和四极子矩），重点是傅里叶求和技术（Stewart, 1979）。该工作给出了电磁感应、电磁感应、电磁感应、电荷密度（包括原子核）、电磁感应梯度和电荷密度梯度的综合表达式。重要的是，它还提供了方法的细节（可以推广到高阶内矩），讨论了ESP的起源项，实验数据的有限分辨率（因此各种性质的收敛行为和级数终止的影响），并观察到基于傅立叶系数的结果，包括变形电子密度的振动（或热）平均，在远离原子核的区域非常接近静态结果。20世纪80年代初，Stewart小组发表了大量论文，概述了计算ESP、EF和EFG的傅里叶求和、直接空间和组合策略，并以匹兹堡大学Craven小组测量的咪唑和9-甲基腺呤的伪原子多极拟合实验数据为例（Spackman & Stewart, 1981; Stewart, 1982; Spackman & Stewart, 1984）。这种方法后来的应用包括傅立叶/直接空间的组合方法来映射…
The determination of relevant physical properties from the aspherical pseudoatom model and comparison with independent experimental and/or computational results remains a key objective of many modern charge-density studies based on high-resolution lowtemperature X-ray diffraction data. The recent paper published by Volkov, King, Coppens & Farrugia [Acta Cryst.(2006), A62, 400–408](referred to as VKCF in the following) represents an important step towards realizing this goal in routine charge-density analyses. It presented new and improved formulae for calculating the electrostatic potential (ESP), electric field (EF) and electric field gradient (EFG) from the aspherical pseudoatom model, with applications made to both experimental and model sets of structure factors. Of considerable practical importance, these expressions have been incorporated in a new version of XDPROP, part of the XD package now in widespread use (Koritsanszky et al., 2003). This Letter aims to complement the work described by VKCF by providing a broader perspective on some of the issues raised in that work, and commenting on some of the results presented by them. VKCF write (p. 401) that ‘Various methods for calculating the ESP from X-ray diffraction data have been described and consequently applied in the literature. These methods can basically be split into two very different groups:(i) directly from experimentally measured structure factors (Bertaut, 1978; Schwarzenbach & Thong, 1979; Stewart, 1979) and (ii) from static models of the electron density.’It is important to recognize that the group identified as (i) is not restricted to experimental measurements, and can be applied much more broadly to any set of valid structure factors (eg static, computed from the aspherical pseudoatom model, as discussed further below). Moreover, there is an intimate relationship between approaches (i) and (ii), and many properties in the crystal are most advantageously computed via a combination of the two approaches. This aspect of the determination of the ESP, EF and EFG from X-ray diffraction data was clearly outlined several decades ago by RF Stewart, and Stewart’s paper cited by VKCF discussed the determination of ‘inner moments’(ie averages that involve negative powers of r, as opposed to ‘outer moments’ such as the dipole and quadrupole moments, which involve zero and positive powers of r) from X-ray diffraction data, with a focus on Fourier summation techniques (Stewart, 1979). That work presented comprehensive expressions for the determination of the ESP, EF, EFG, charge density (ie including nuclei), gradient of the EFG and gradient of the charge density. Importantly, it also provided details of the method (which can be generalized to inner moments of higher order), discussed the origin term for the ESP, the finite resolution of experimental data (and hence convergence behaviour of the various properties and the effects of series termination), and observed that results based on Fourier coefficients incorporating vibrational (or thermal) averaging of deformation electron densities closely approximate static results in regions far from the nuclei.A number of papers that emerged from Stewart’s group in the early 1980s outlined Fourier summation, direct space and combined strategies for the computation of the ESP, EF and EFG, with examples drawn from pseudoatom multipole fits to experimental data for imidazole and 9-methyladenine measured by Craven’s group at the University of Pittsburgh (Spackman & Stewart, 1981; Stewart, 1982; Spackman & Stewart, 1984). Later applications of this kind included a combined Fourier/direct-space approach to mapping the …
晶体衍射的分子静电势：神经递质 γ-氨基丁酸。
影响因子：
3.4
作者：
Stewart,RF;Craven,BM
通讯作者：
Craven,BM