The Pfizer Institute for Pharmaceutical Materials Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
J Chem Theory Comput. 2008 Oct 14;4(10):1795-805. doi: 10.1021/ct800195g.
The computer-generation of the crystal structures of the α-amino acid valine is used as a challenging test of lattice energy modeling methods for crystal structure prediction of flexible polar organic molecules and, specifically, to examine the importance of molecular polarization on calculated relative energies. Total calculated crystal energies, which combine atom-atom model potential calculations of intermolecular interactions with density functional theory intramolecular energies, do not effectively distinguish the real (known) crystal structures from the rest of the low energy computer-generated alternatives when the molecular electrostatic models are derived from isolated molecule calculations. However, we find that introducing a simple model for the bulk crystalline environment when calculating the molecular energy and electron density distribution leads to important changes in relative total crystal energies and correctly distinguishes the observed crystal structures from the set of computer-generated possibilities. This study highlights the importance of polarization of the molecular charge distribution in crystal structure prediction calculations, especially for polar flexible molecules, and suggests a computationally inexpensive approach to include its effect in lattice energy calculations.
使用计算机生成α-氨基酸缬氨酸的晶体结构，作为对用于预测柔性极性有机分子晶体结构的晶格能建模方法的挑战性测试，特别是考察分子极化对计算相对能量的重要性。当从孤立分子计算中推导出分子静电模型时，将结合原子-原子模型势能计算的分子间相互作用与密度泛函理论的分子内能量相结合的总计算晶体能量，并不能有效地将真实（已知）晶体结构与其余低能量计算机生成的替代结构区分开来。然而，我们发现，在计算分子能量和电子密度分布时引入简单的晶态环境模型会导致相对总晶体能量发生重要变化，并正确地区分观察到的晶体结构与计算机生成的可能性集。这项研究强调了在晶体结构预测计算中，特别是对于极性柔性分子，分子电荷分布极化的重要性，并提出了一种计算成本低廉的方法来在晶格能计算中包含其影响。
