Dear GROMACS user, Hello. I am new to molecular dynamics simulation, and also to simulation of interface. Recently I have simulated liquid-vapor interface of heptane in a slab with NVT ensemble, and liquid-liquid inteface of water-heptane in NPzAT ensemble. I am using GROMOS force field and SPC/E water model. Using g_density, I obtained the density profile of each system across the z direction of my simulation box. I have two questions I want to ask all of you.
1. In GROMACS, how can I calculate the thickness of these interfaces? I have checked through the manual, and I couldn't find any command for this purpose. 2. What is the expression used for calculating the density profile of liquid-vapor and liquid-liquid interface by g_density? I have gone through the gmx_density.c code and unfortunately I couldn't understand it at the moment due to my zero experience in programming. In a paper I saw that one author use this equation to determine the coexistence densities between liquid and vapor interface: rho(z) = 0.5 [rho(liquid) + rho(vapor)] - 0.5 [rho(liquid) - rho(vapor)] tanh [(z-z0)/d]. z is the z direction of the box, z0 is location of the Gibbs dividing surface, and d is the interface thickness. Is the g_density command also based on that equation? Best regards, Widya
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