Applied Physics, RMIT University, GPO Box 2476 V, Victoria 3001, Australia.
J Phys Chem B. 2009 Oct 1;113(39):12988-98. doi: 10.1021/jp9038368.
We study the role of short-range directional interactions in coarse-graining (CG) of protic (i.e., acetamide, methanol, ethanol, and water) and aprotic (i.e., acetone, benzene, and toluene) liquids at normal conditions. For this purpose, we introduce a new CG method in which the average interactions between atomistic molecules and CG beads measured in an N,P,T ensemble are preserved. We show that the spherically symmetric effective CG potential constructed according to our scheme is able to reproduce structural/thermodynamic properties of aprotic liquids; the heat of vaporization and total bonding energy profile for monomer are reproduced with good accuracy, while the density and radial distribution function are reproduced with fair accuracy within the proposed method. In contrast, the isobaric heat capacity is underestimated in the CG simulation because some of the fluctuations have been washed out from atomistic aprotic liquids. For protic liquids, spherically symmetric effective CG potential produces more structure, enhanced packing of beads, and underestimated isobaric heat capacity of CG liquids. This fundamental difference between protic and aprotic liquids can be explained by the presence of short-range directional interactions in the former liquids. We conclude that some information during the CG into spherically symmetric interaction potentials of protic liquids has to be lost. However, understanding how short-range directional interactions influence the structural and thermodynamic properties of the CG liquids seems to be the key for improving the CG methods.
我们研究了短程定向相互作用在质子（即乙酰胺、甲醇、乙醇和水）和非质子（即丙酮、苯和甲苯）液体的粗粒化（CG）中的作用。为此，我们引入了一种新的 CG 方法，其中在 N，P，T 系综中测量的原子分子与 CG 珠之间的平均相互作用得到了保留。我们表明，根据我们的方案构造的具有球形对称的有效 CG 势能能够重现非质子液体的结构/热力学性质；单体的汽化热和总键合能分布得到了很好的重现，而密度和径向分布函数在提出的方法内得到了较好的重现。相比之下，CG 模拟中的等压热容被低估了，因为一些波动已经从原子非质子液体中被冲刷掉了。对于质子液体，球形对称的有效 CG 势能产生更多的结构，增强了珠的堆积，并且 CG 液体的等压热容被低估。质子液体和非质子液体之间的这种基本差异可以用前者液体中短程定向相互作用的存在来解释。我们得出结论，在 CG 到质子液体的球形对称相互作用势能的过程中，必须丢失一些信息。然而，理解短程定向相互作用如何影响 CG 液体的结构和热力学性质似乎是改进 CG 方法的关键。
