lammps.js

Run LAMMPS directly in the browser — a WebAssembly build with TypeScript-ready bindings. The package exports the compiled lammps.js module together with a modern interface (LAMMPSWeb) that exposes snapshots for particles, bonds and simulation box data.

Usage

import { LammpsClient } from "lammps.js/client";

const lammps = await LammpsClient.create();

lammps.start().runScript(`
  units lj
  atom_style atomic
  lattice fcc 0.8442
  region box block 0 3 0 3 0 3
  create_box 1 box
  create_atoms 1 box
  mass 1 1.0
  pair_style lj/cut 2.5
  pair_coeff 1 1 1.0 1.0 2.5
  run 1
`);

const particles = lammps.syncParticles({ copy: true });
console.log(`atoms: ${particles.count}`);

const wrapped = lammps.syncParticles({ wrapped: true, copy: true });
console.log(`wrapped positions length: ${wrapped.positions.length}`);

lammps.dispose();

Advance the solver (via advance(stepCount, applyPre?, applyPost?)) between snapshots to receive new frames.

Advance the solver (advance(stepCount, applyPre?, applyPost?)) before sampling to obtain subsequent frames. The TypeScript definitions are shipped with the package under types/index.d.ts, so IDEs receive auto-complete everywhere.

High-level client

For a more ergonomic API, use the helpers in lammps.js/client:

import { LammpsClient } from "lammps.js/client";

const lammps = await LammpsClient.create();
await fetch("/in.lj")
  .then(res => res.text())
  .then(script => lammps.runInput("in.lj", script));

for (let frame = 0; frame < 10; frame += 1) {
  lammps.advance(1, false, false);
  const { positions, count } = lammps.syncParticles({ copy: true });
  console.log(`frame ${frame}: ${count} atoms`);
}

lammps.dispose();

Advance the solver (via advance(stepCount, applyPre?, applyPost?)) between snapshots to receive new frames.

Use syncParticles({ wrapped: true }) and syncBonds({ wrapped: true }) to access raw periodic coordinates while the default returns minimum-image data, ready for rendering.

Install via npm:

npm install lammps.js

Building the wasm bundle

npm run build:wasm

This calls cpp/build.py, which keeps the upstream LAMMPS checkout in cpp/lammps fresh and emits cpp/lammps.js (single-file ES module).

Test suite

The Vitest suite spins up a jsdom environment, instantiates the wasm module, loads a miniature Lennard-Jones sample and validates the public interface.

npm test

The build step fetches the LAMMPS sources on first run. Subsequent runs are incremental thanks to the cached checkout and Emscripten cache.

Examples

A ready-to-run Three.js demo lives in examples/threejs:

cd examples/threejs
npm install
npm run dev

It links against the local workspace copy of lammps.js and renders the Lennard-Jones sample (tests/fixtures/lj.mini.in).