Department of Physical Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28, Prague 6, Czech Republic.
Chemphyschem. 2020 Jun 3;21(11):1184-1194. doi: 10.1002/cphc.202000108. Epub 2020 May 12.
Sublimation enthalpies of alkane-α,ω-diamines exhibit an odd-even pattern within their homologous series. First-principles calculations coupled with the quasi-harmonic approximation for crystals and with the conformation mixing model for the ideal gas are used to explain this phenomenon from the theoretical point of view. Crystals of the odd and even alkane-α,ω-diamines distinctly differ in their packing motifs. However, first-principles calculations indicate that it is a delicate interplay of the cohesive forces, phonons, molecular vibrations and conformational equilibrium which governs the odd-even pattern of the sublimation enthalpies within the homologous series. High molecular flexibility of the alkane-α,ω-diamines predetermines higher sensitivity of the computational model to the quality of the optimized geometries and relative conformational energies. Performance of high-throughput computational methods, such as the density functional tight binding (DFTB, GFN2-xTB) and the explicitly correlated dispersion-corrected Møller-Plesset perturbative method (MP2C-F12), are benchmarked against the consistent state-of-the-art calculations of conformational energies and interaction energies, respectively.
烷烃-α,ω-二胺的升华焓在同系物中呈现出奇-偶规律。本文从理论角度，利用晶体的准谐近似和理想气体的构象混合模型，结合第一性原理计算，对这一现象进行了解释。奇数和偶数烷烃-α,ω-二胺的晶体在堆积方式上明显不同。然而，第一性原理计算表明，是内聚能、声子、分子振动和构象平衡之间的微妙相互作用，决定了同系物中升华焓的奇-偶规律。烷烃-α,ω-二胺的高分子柔韧性预先决定了计算模型对优化几何形状和相对构象能的质量的更高敏感性。密度泛函紧束缚（DFTB、GFN2-xTB）和显式相关色散校正的 Møller-Plesset 微扰方法（MP2C-F12）等高通量计算方法的性能，分别与构象能和相互作用能的一致最先进计算进行了基准测试。
