Molecular Dynamics: Phases of Matter
A few hundred atoms interact through the Lennard-Jones potential — harsh repulsion up close, gentle van der Waals attraction further out — and are integrated with the velocity-Verlet algorithm in a periodic box, using a cell-list neighbour search and a Berendsen thermostat that nudges the kinetic energy toward your target temperature. Start hot and the box is a structureless gas; drag the temperature down and atoms condense into liquid droplets, then lock into hexagonally packed crystal rafts — three phases of matter from a single pair force. Atoms are coloured by kinetic energy from cold blue through white to hot orange, and you can drag through the box to stir the fluid. Particle-count and density sliders reshape the box, and live readouts report the instantaneous temperature and the potential energy per atom.
Runs 100% in your browser — simulations are computed locally on your device.
Read the full guide to this tool
Notes
- The potential V(r) = 4ε[(σ/r)¹² − (σ/r)⁶] was proposed by John Lennard-Jones in 1924: the r⁻⁶ tail is the physically correct induced-dipole attraction, the r⁻¹² core a computational convenience.
- Velocity Verlet is time-reversible and symplectic, so energy stays honest over long runs — Loup Verlet used it to simulate liquid argon in 1967, one of the first molecular-dynamics computations.
- Freezing in two dimensions is special: true long-range positional order is forbidden (Mermin–Wagner), and melting is predicted to pass through a "hexatic" phase via unbinding defects (KTHNY theory).
- Runs 100% in your browser — simulations are computed locally on your device.
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