dmf.in (10.7 KB)
DMF.mol (989 Bytes)
lmp_29Aug_2024.out (13.5 KB)
nohup_lmp_Aug_2023.out (29.7 KB)
Hello everyone,
I am using LAMMPS (29Aug2024) to simulate 450 rigid DMF (Dimethyl Formamide) molecules with united-atom methyl groups under ambient conditions. To enforce rigidity, I am using fix rigid/npt/small with a timestep of 0.2 fs.
After 300,000 steps, the potential energy and simulation box size appear reasonable. However, as the number of timesteps increases, the simulation box unexpectedly deforms along the z-axis.
To investigate, I ran an NVT simulation, which revealed that the pressure is 135 atm instead of 1 atm in a box of 50 Angstroms.
The same simulation runs without any issues in the Aug/2023 LAMMPS version, producing expected results (density = 0.943 g/cm³, potential energy = 44.22 kJ/mol, pressure = 1.08 atm, temperature = 298.55 K).
I have attached:
nohup.out files from both LAMMPS versions showing the box size evolution.
The DMF.mol file.
My input script.
A JPEG file showing the CS2_M potential and atom numbering.
Any insights or suggestions would be greatly appreciated.
Regards
Costas Vlahos