gromacs

name	gromacs
description	Use when setting up and running biomolecular MD simulations with GROMACS. Generate topologies, write MDP input files, execute simulations, and perform basic analysis.

GROMACS - Molecular Dynamics Simulation

Overview

GROMACS is a high-performance engine for biomolecular MD simulations, including proteins, lipids, and nucleic acids in explicit solvent.

When to Use GROMACS vs. Other Tools

Scenario	Recommended Tool	Why
Biomolecular systems (proteins, membranes, DNA) in explicit solvent	GROMACS	Optimized force fields, extensive biophysical analysis tools
Materials, coarse-grained, or reactive MD	LAMMPS	Flexible potentials, ReaxFF, granular/CG support
Quick structure conversion or small test calculations	ASE	Lightweight Python interface, many calculators

Key rule: Use GROMACS when the system is biomolecular and you need production-quality explicit-solvent MD with thermodynamic analysis.

Requirements

GROMACS must be installed and gmx must be available in your PATH.

Core Capabilities

1. Write MDP Files

Generate standard MDP files for common protocols.

python scripts/write_mdp.py em minimization.mdp
python scripts/write_mdp.py nvt equilibration.mdp
python scripts/write_mdp.py npt production.mdp

2. Run Simulations

Prepare and run simulations.

python scripts/run_simulation.py --mdp production.mdp --gro system.gro --top system.top --o run.tpr --run

3. Run Analysis

Compute RMSD, RMSF, and RDF.

python scripts/run_analysis.py --xtc traj.xtc --gro system.gro --task rmsd --o rmsd.xvg

Anti-Patterns (Do Not Do These)

• Do not skip energy minimization before equilibration. Bad contacts cause immediate crashes or LINCS failures.
• Do not start NPT production without NVT equilibration first. Temperature coupling must stabilize before pressure coupling is turned on.
• Do not use a time step larger than 2 fs without constraints. Unconstrained bonds to hydrogen require dt <= 1 fs.
• Do not ignore LINCS warnings. They indicate an unstable integrator or a poor starting structure.
• Do not run analysis on raw trajectories without considering periodic boundary conditions (PBC). Molecules may appear broken across box boundaries.

Best Practices

• Always minimize before equilibration.
• Run NVT first, then NPT, then production.
• Use dt = 0.002 with bond constraints (e.g., constraints = h-bonds).
• Use PME for long-range electrostatics in biomolecular systems.
• Write coordinates every 5–10 ps (nstxout = 5000 at 2 fs/step) to balance disk usage and analysis resolution.
• Set gen_seed for reproducibility when generating velocities.
• For questions about the latest GROMACS features, new MDP options, or version-specific syntax changes, use WebFetch on https://manual.gromacs.org/current/ before answering.

Common Errors and Fixes

Error / Symptom	Likely Cause	Fix
grompp fails with "atomtype not found"	Missing force-field parameters or wrong topology path	Check *.itp includes and force-field selection
mdrun crashes with LINCS warnings	Too-large time step or poorly minimized structure	Reduce dt, increase nsteps in EM, or check clashes
Energy or temperature drift	Cutoffs too short, missing constraints, or integration errors	Increase rcoulomb/rvdw, verify constraints, reduce dt
Analysis shows broken molecules	PBC not handled	Use gmx trjconv -center -pbc mol before analysis
Fatal error: number of coordinates does not match	Atom count mismatch between .gro and .top	Reconcile topology with structure (e.g., missing water or ions)

References

• Official Documentation: https://manual.gromacs.org/current/
• Tutorials: https://tutorials.gromacs.org/
• GitHub: https://gitlab.com/gromacs/gromacs

Getting Live Information

If the user asks about recently added features, new options, or version-specific syntax changes, use WebFetch on the official documentation at https://manual.gromacs.org/current/ before answering.