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:
-
2 ns of NPT equilibration
-
4 ns of NVT production
-
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