Crystal-field effects in l-homoserine: multipoles versus quantum chemistry
Crystal-field effects in l-homoserine: multipoles versus quantum chemistry
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DOI：
10.1107/s0108767312013001
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发表时间：
2012-07-01
影响因子：
1.8
通讯作者：
Jayatilaka, D.
中科院分区：
文献类型：
--
作者：
Dittrich, B.;Sze, E.;Jayatilaka, D.
与具有相同几何形状的孤立分子相比，结晶固态分子的电子密度受到周围分子的场和分子间氢键的影响。这些影响尚未在分子电子密度分布水平上进行广泛的研究，这可以从高分辨率 X 射线单晶衍射以及从头算量子化学中获得。为了研究非标准氨基酸 L-高丝氨酸的“晶体场效应”，采用了三种方法：（i）从头开始点电荷分离分子模型； (ii) 使用具有或不具有周围点电荷和偶极子的赫什菲尔德原子进行结构细化； (iii) 使用密度泛函理论进行基准周期计算。对于（i）和（iii），多极模型适合静态结构因子。从各自的晶体模型和孤立分子计算获得的电子密度之间的差异产生了有关晶体场效应和偶极矩增强的详细信息。点电荷模型产生的相互作用密度特征与周期性从头量子化学的特征非常一致。另一方面，多极模型无法重现两性离子高丝氨酸相互作用密度的精细细节。
In contrast to an isolated molecule with identical geometry, the electron density of a molecule in the crystalline solid state is influenced by the field of surrounding molecules and by intermolecular hydrogen bonding. These influences have not yet found wide study on the level of the molecular electron-density distribution, which can be obtained both from high-resolution X-ray single-crystal diffraction as well as from ab initio quantum chemistry. To investigate this `crystal-field effect' on the non-standard amino acid l-homoserine, three approaches were taken: (i) an ab initio point-charge isolated-molecule model; (ii) structure refinement with Hirshfeld atoms with and without surrounding point charges and dipoles; (iii) benchmark periodic calculations using density functional theory. For (i) and (iii) multipole models were fitted to static structure factors. The difference between the electron density obtained from the respective in-crystal model and from the isolated-molecular calculations yields detailed information on the crystal-field effect and dipole-moment enhancements. The point-charge model produces features of interaction density which are in good agreement with those from periodic ab initio quantum chemistry. On the other hand the multipole model is unable to reproduce fine details of the interaction density for zwitterionic homoserine.