Department of Chemical Engineering, Brigham Young University, Provo, Utah 84602, USA.
J Chem Phys. 2017 May 21;146(19):194110. doi: 10.1063/1.4983406.
Molecular simulation has the ability to predict various physical properties that are difficult to obtain experimentally. For example, we implement molecular simulation to predict the critical constants (i.e., critical temperature, critical density, critical pressure, and critical compressibility factor) for large n-alkanes that thermally decompose experimentally (as large as C). Historically, molecular simulation has been viewed as a tool that is limited to providing qualitative insight. One key reason for this perceived weakness in molecular simulation is the difficulty to quantify the uncertainty in the results. This is because molecular simulations have many sources of uncertainty that propagate and are difficult to quantify. We investigate one of the most important sources of uncertainty, namely, the intermolecular force field parameters. Specifically, we quantify the uncertainty in the Lennard-Jones (LJ) 12-6 parameters for the CH, CH, and CH united-atom interaction sites. We then demonstrate how the uncertainties in the parameters lead to uncertainties in the saturated liquid density and critical constant values obtained from Gibbs Ensemble Monte Carlo simulation. Our results suggest that the uncertainties attributed to the LJ 12-6 parameters are small enough that quantitatively useful estimates of the saturated liquid density and the critical constants can be obtained from molecular simulation.
分子模拟具有预测各种难以通过实验获得的物理性质的能力。例如，我们通过分子模拟来预测在实验中热分解（如 C 以上）的大烷烃的临界常数（即临界温度、临界密度、临界压力和临界压缩因子）。从历史上看，分子模拟一直被视为一种仅限于提供定性见解的工具。分子模拟被认为存在这种弱点的一个关键原因是难以量化结果的不确定性。这是因为分子模拟有许多传播且难以量化的不确定性来源。我们研究了其中一个最重要的不确定性来源，即分子间力场参数。具体来说，我们量化了 CH、CH 和 CH 统一原子相互作用位点的 Lennard-Jones (LJ) 12-6 参数的不确定性。然后，我们展示了参数中的不确定性如何导致 Gibbs 系综蒙特卡罗模拟中获得的饱和液体密度和临界常数值的不确定性。我们的结果表明，归因于 LJ 12-6 参数的不确定性足够小，以至于可以从分子模拟中获得定量有用的饱和液体密度和临界常数的估计值。
