Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA.
J Phys Chem B. 2011 Apr 7;115(13):3452-65. doi: 10.1021/jp1063935. Epub 2011 Mar 11.
Coarse-grain potentials allow one to extend molecular simulations to length and time scales beyond those accesssible to atomistic representations of the interacting system. Since the coarse-grain potentials remove a large number of interaction sites and, hence, a large number of degrees of freedom, it is generally assumed that coarse-grain potentials are not transferable to different systems or state points (temperature and pressure). Here we apply lessons learned from the parametrization of transferable atomistic potentials to develop a systematic procedure for the parametrization of transferable coarse-grain potentials. In particular, we apply an iterative Boltzmann optimization for the determination of the bonded interactions for coarse-grain beads belonging to the same molecule and separated by one or two coarse-grain bonds and parametrize the nonbonded interactions by fitting to the vapor-liquid coexistence curves computed for selected molecules represented by the TraPPE-UA (transferable potentials for phase equilibria-united atom) force field. This approach is tested here for linear alkanes where parameters for C(3)H(7) end segments and for C(3)H(6) middle segments of the TraPPE-CG (transferable potentials for phase equilibria-coarse grain) force field are determined and it is shown that these parameters yield quite accurate vapor-liquid equilibria for neat n-hexane to n-triacontane and for the binary mixture of n-hexane and n-hexatriacontane. In addition, the position of the first peak in various radial distribution functions and the coordination number for the first solvation shell are well reproduced by the TraPPE-CG force field, but the first peaks are too high and narrow.
粗粒化势允许将分子模拟扩展到超出相互作用系统的原子表示法可访问的长度和时间尺度。由于粗粒化势去除了大量的相互作用位点，因此也去除了大量的自由度，因此通常假定粗粒化势不能转移到不同的系统或状态点（温度和压力）。在这里，我们从可转移原子势的参数化中吸取教训，开发了一种系统的可转移粗粒化势参数化方法。特别是，我们应用迭代玻尔兹曼优化来确定属于同一分子的粗粒化珠之间的键相互作用，并用拟合蒸汽-液体共存曲线的方法来参数化非键相互作用，这些曲线是为代表 TraPPE-UA（用于相平衡的可转移势-统一原子）力场的选定分子计算的。在这里，我们将这种方法应用于线性烷烃，确定了 TraPPE-CG（用于相平衡的可转移势-粗粒化）力场中 C(3)H(7)末端片段和 C(3)H(6)中间片段的参数，并表明这些参数对于纯净的正己烷到正三十烷以及正己烷和正三十六烷的二元混合物都能得到相当准确的汽液平衡。此外，TraPPE-CG 力场很好地再现了各种径向分布函数中的第一个峰和第一个溶剂化壳的配位数，但第一个峰太高太窄。
