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 (Epot), 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 (Tc,exp = 425.0 K, ρc,exp = 245 kg/m3, Pc,exp = 43.2 bar and Tc,ρ = 430.25 ± 2.50 K, ρc,ρ = 234.25 ± 2.66 kg/m3, Pc,ρ = 39.09 ± 0.73 bar), while from the SSA and potential energy the critical temperature can be reproduced within 1% of deviation (Tc,SSA = 426.5, Tc,Epot = 426.0 K).