Molecular interactions encode macroscopic phenomena. Molecular dynamics simulations (MD) based on classical force fields can provide structural and energetic information about phase equilibrium at different conditions as well as about systems above the critical point. In this study, vapor/liquid interface of 1,3-butadiene is investigated using classical MD and Two Phase Molecular Dynamics (2ϕMD) techniques in order to test force field parameters as well as to analyze structural and energetic details from ambient conditions to the supercritical phase. A new approach is proposed based on Voronoi-tessellation to categorize vapor, liquid and ‘phase transferring’ molecules.

The force field (OPLS-AA with 1.14*CM1A partial atomic charges) combined with the 2ϕMD method is used to reproduce experimental data (density and surface tension) of 1,3-butadiene well for all investigated phases. Density (ρ), potential energy (E_pot), surface tension (γ) and specific surface area (SSA) based methods have also been tested to calculate the critical parameters of the molecular system. It is found that the density based approach is the best alternative for retrieving experimental data for the critical point (T_c,exp = 425.0 K, ρ_c,exp = 245 kg/m³, P_c,exp = 43.2 bar and T_c,ρ = 430.25 ± 2.50 K, ρ_c,ρ = 234.25 ± 2.66 kg/m³, P_c,ρ = 39.09 ± 0.73 bar), while from the SSA and potential energy the critical temperature can be reproduced within 1% of deviation (T_c,SSA = 426.5, T_c,Epot = 426.0 K).

分子相互作用编码宏观现象。基于经典力场的分子动力学模拟（MD）可以提供有关不同条件下的相平衡以及高于临界点的系统的结构和能量信息。在这项研究中，使用经典的MD和两相分子动力学（2ϕMD）技术研究了1,3-丁二烯的气/液界面，以便测试力场参数以及分析从环境条件到超临界的结构和能量细节。相。提出了一种基于Voronoi镶嵌的新方法，以对蒸气，液体和“相转移”分子进行分类。

力场（带有1.14 * CM1A部分原子电荷的OPLS-AA）与2ϕMD方法相结合，用于再现所有研究阶段的1,3-丁二烯井的实验数据（密度和表面张力）。还测试了基于密度（ρ），势能（E _pot），表面张力（γ）和比表面积（SSA）的方法来计算分子系统的关键参数。发现基于密度的方法是检索临界点实验数据的最佳选择（T _c，exp  = 425.0 K，ρc _，exp  = 245 kg / m ³，P _c，exp  = 43.2 bar和T _{c ，ρ}  = 430.25±2.50 K， ρc _，ρ = 234.25±2.66 kg / m ³，P _c，ρ  = 39.09±0.73 bar），而根据SSA和势能，临界温度可在偏差的1％之内再现（T _c，SSA  = 426.5，T _c，Epot  = 426.0 K）。