# IFT in CG simulation using MARTINI 3.0 **URL:** \ **Category:** User discussions\ **Tags:** forcefield\ **Created:** [June 9, 2026, 11:26pm UTC](https://gromacs.bioexcel.eu/t/ift-in-cg-simulation-using-martini-3-0/13522 "2026-06-09T23:26:33Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![promovr](https://avatars.discourse-cdn.com/v4/letter/p/9de053/32.png) [@promovr](https://gromacs.bioexcel.eu/u/promovr)\ **Post date:** [June 9, 2026, 11:26pm UTC](https://gromacs.bioexcel.eu/t/ift-in-cg-simulation-using-martini-3-0/13522/1 "2026-06-09T23:26:33Z")
GROMACS version: 2026.0 GROMACS modification: No Dear GROMACS community, I am trying to simulate an “island-type” asphaltene model using the Martini 3.0 force field. I performed the CG mapping in Materials Studio 2024 and built my simulation box consisting of heptane (bottom), asphaltene (middle), and water (top). After successfully running the simulation, I am facing an issue with the interfacial tension (IFT). Even after calibrating the Lennard-Jones `epsilon` parameter for the `TC5` (asphaltene bead) - `C1` (heptane bead) interaction, I cannot achieve the expected IFT values (which should be around 1100 bar·nm). **My simulation protocol:** 1. 2 ns of NPT equilibration 2. 4 ns of NVT production 3. IFT is calculated from the last 2 ns of the NVT trajectory. Despite the calibration, the resulting IFT remains far from the target. What could be interfering with the IFT in this setup? Could it be related to the equilibration protocol, the choice of barostat, or perhaps the way I am calculating the IFT in GROMACS? I would be grateful for any suggestions or pointers on what else I could check or adjust. Thank you in advance for your help. NPT: title = NPT\_Martini\_MS\_Replica ; Integração (Igual ao MS: 10 fs, 200k passos = 2 ns) integrator = md dt = 0.010 ; 10 fs nsteps = 200000 ; 2e5 passos nstcalcenergy = 100 nstenergy = 1000 ; TrajectoryFrequency do NPT (1e3) nstlog = 1000 nstxout-compressed = 1000 ; Gravação da trajetória (.xtc) ; Interações não-ligadas (Padrão Martini 3 para estabilidade) cutoff-scheme = Verlet nstlist = 40 rcoulomb = 1.1 rvdw = 1.1 coulombtype = reaction-field epsilon-r = 15 vdw-type = cutoff vdw-modifier = Potential-shift-verlet pbc = xyz ;verlet-buffer-tolerance = 0.005 ; Termostato (Igual ao MS: Nose-Hoover, 300 K) tcoupl = nose-hoover tc-grps = ASF HEP W ; Três grupos automáticos tau\_t = 1.0 1.0 1.0 ; Três valores de tau\_t ref\_t = 300.0 300.0 300.0 ; Três valores de ref\_t ; Barostato (Ajustado do MS para Interface: Berendsen Semi-Isotrópico, 1 bar) pcoupl = Berendsen pcoupltype = isotropic ; Essencial para a física de interfaces/asfalteno tau\_p = 8.0 ; Acoplamento rápido para Berendsen ref\_p = 1.0 ; 0.0001 GPa = 1.0 bar (Plano X/Y e Eixo Z) compressibility = 4.5e-5 gen-vel = yes gen-temp = 300 gen-seed = -1 continuation = no NVT: title = NVT\_Martini\_MS\_Replica ; Integração (Igual ao MS: 10 fs, 400k passos = 4 ns) integrator = md dt = 0.010 ; 10 fs nsteps = 400000 ; 4e5 passos nstcalcenergy = 100 nstenergy = 1000 ; TrajectoryFrequency do NVT (2e3) nstlog = 1000 nstxout-compressed = 1000 ; Gravação da trajetória (.xtc) ; Interações não-ligadas (Mantido padrão estável) cutoff-scheme = Verlet nstlist = 40 rcoulomb = 1.1 rvdw = 1.1 coulombtype = reaction-field epsilon-r = 15 vdw-type = cutoff vdw-modifier = Potential-shift-Verlet pbc = xyz ;verlet-buffer-tolerance = 0.005 ; Termostato (Igual ao MS: Nose-Hoover, 300 K) tcoupl = nose-hoover tc-grps = ASF HEP W ; Três grupos automáticos tau\_t = 1.0 1.0 1.0 ; Três valores de tau\_t ref\_t = 300.0 300.0 300.0 ; Três valores de ref\_t ; Sem Barostato (Ensemble NVT) pcoupl = no continuation = yes ---
**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\ **Post date:** [June 12, 2026, 8:41am UTC](https://gromacs.bioexcel.eu/t/ift-in-cg-simulation-using-martini-3-0/13522/2 "2026-06-12T08:41:39Z")
I don’t understand you setup. You seem to have three layers. So you have surface tension contributions from water-asphaltene and asphaltene-heptane. But what happens around the periodic boundary? Do you have a water-heptane interface? Or a water-vacuum and a heptane-vacuum interface? There interfaces will also contribute to the total surface tension.