LAMMPS Script Validation & Generation

When to use: Validate LAMMPS input scripts (.in files) for syntax errors and parameter conflicts before running MD simulations. Generate LAMMPS input scripts from workflow node parameters.

Prerequisites:

• LAMMPS installed on HPC or local system
• Input structure (PDB, MOL2, or LAMMPS data file)
• Understanding of potential types and force fields

Workflow Steps

1. Validate Existing LAMMPS Script

If you have a custom in.lammps script:

• Check syntax errors (missing semicolons, invalid commands)
• Verify command ordering (bond_style before read_data, etc.)
• Confirm parameter compatibility (e.g., PPPM with charged atoms)
• Detect mismatches between script and data file

# Use the validation skill
Input: in.lammps script content
Output: List of errors or "Script is valid"

2. Generate LAMMPS Script from Parameters

If you have workflow node parameters (potential type, temperature, steps, etc.):

• Auto-generate correct command sequence
• Set force field parameters automatically
• Include ensemble fixes (NVT/NPT/NVE)
• Add thermodynamic output and trajectory dumps

# Use the generation skill
Input: Node parameters (potential_type, temperature, steps, etc.)
Output: Complete in.lammps script ready to run

3. Workflow Integration

In CatGo MD nodes:

1. MD Node — Classical MD simulations with NVT/NPT/NVE ensembles
2. MD Minimize Node — Energy minimization with conjugate gradient or FIRE
3. Packmol Option — Build initial box from molecules (MD Minimize only)

Key Parameters

Potential Type

• Force Field (GAFF2, OPLS-AA, COMPASS) — Auto-generates bonds, angles, charges
• Lennard-Jones — Simple pair-wise LJ potential
• CHARMM — With long-range Coulomb (PPPM kspace)
• Buckingham — For ionic materials
• EAM — For metals (copper, aluminum, etc.)
• Tersoff — For covalent materials (Si, Ge)
• Custom — Manual pair_style and coefficients

Ensemble

• NVE — Microcanonical (constant energy)
• NVT — Canonical (constant temperature, Berendsen thermostat)
• NPT — Isothermal-isobaric (constant T and P)
• Minimize — Energy minimization (CG, SD, FIRE)

Force Field Settings

Auto-configured based on potential type:

Potential	Pair Style	Kspace	Bond/Angle
Force Field	lj/charmm/coul/long	PPPM	Auto
CHARMM	lj/charmm/coul/long	PPPM	harmonic
OPLS-AA	lj/charmm/coul/long	PPPM	harmonic
EAM	eam/alloy	None	N/A
Tersoff	tersoff	None	N/A

Common Issues & Fixes

Issue: "Pair style mismatch with data file"

Cause: Data file has bonds but script uses atom_style=atomic Fix: Change atom_style to "full" or "molecular"

Issue: "PPPM setup error"

Cause: Using PPPM without charged atoms or with non-periodic boundary Fix: Remove kspace_style or set boundary to periodic (ppp)

Issue: "Minimize never converges"

Cause: Energy tolerance (etol) too small or maxiter too low Fix: Increase etol to 1e-4 or maxiter to 50000

Issue: "Temperature oscillates wildly in NVT"

Cause: Thermostat damping too large or timestep too large Fix: Reduce timestep or adjust thermostat Tdamp parameter

Example Workflows

Minimize LJ fluid

Structure (PDB) → MD Minimize Node
  - Potential: Lennard-Jones
  - Min Style: CG
  - Max Iter: 10000
  - Etol: 1e-6
→ Output: trajectory.dump, system_minimized.data

Pack and relax water

Water molecule (PDB) → MD Minimize Node
  - Packmol: enabled (100 molecules, 1.0 g/cm³)
  - Force Field: GAFF2
  - Charge: Gasteiger
  - Min Style: FIRE
  - Etol: 1e-4
→ Output: packed structure, minimized trajectory

NVT MD for protein

Protein structure (PDB) → MD Node
  - Force Field: OPLS-AA
  - Ensemble: NVT
  - Temperature: 300 K
  - Steps: 100000
  - Timestep: 1.0 fs
→ Output: trajectory.dump, thermodynamic data

Validation Checklist

Before running MD:

• Data file has atoms matching atom_style
• Pair style compatible with potential type
• Bonds/angles only if molecule or full atom_style
• Kspace only if periodic (ppp) with charged atoms
• Timestep < 5 fs (1 fs typical for all-atom)
• Thermo freq < total steps
• Dump freq for trajectory output
• Temperature/pressure values reasonable
• Min_style and tolerances set for minimization

References

• LAMMPS Manual: https://lammps.sandia.gov/doc/Manual.html
• Force Field Database: https://www.ff14sb.net/ (AMBER)
• OPLS-AA Parameters: https://zarbi.chem.yale.edu/oplsaal/