Warming the sample…
Melting and boiling points in this dataset are Celsius numbers from the element pages. The slider is Kelvin, because that is the scale kinetic theory actually uses. Below Tm the 64 particles rattle on a lattice. Between Tm and Tb they slip. Past Tb they fly and bounce off the box.
A cartoon, labeled as one
This is not molecular dynamics. There is no pair potential, no thermostat, and no periodic replica of a crystal. The switch at Tm and Tb is a stage direction: lock, slip, fly. Use it to watch kinetic energy compete with cohesion. Do not use it to predict a phase diagram. Helium boils at 4.2 K, so “room temperature” is already a gas. Tungsten, however, is still a rattling solid at thousands of kelvin.
The particles are atoms of the selected element, not molecules. Water is a compound, so its melting point is not on this list. If you want a metal that actually melts in range, pick sodium or mercury. The packing of a real solid is on the unit-cell page.
Questions this box answers
Is this a real molecular-dynamics simulation?
No. It is Verlet motion with three canned behaviors — rattling on lattice sites, slipping with weak cohesion, and free flight. The page then switches those behaviors at this dataset’s melting and boiling points. Use it to see kinetic theory. Do not use it to predict a phase diagram.
Why does helium start as a gas?
Helium’s boiling point is 4.2 K. Room temperature is already far into the gas field. Drag the slider to 0 K to freeze the cartoon lattice. The real solid, however, needs pressure as well as cold, which this box does not model.
What are the particles?
They stand for atoms of the selected element, not molecules. Water’s melting point is not on this list because H₂O is a compound. Pick Fe or Na if you want a metal that actually melts in the slider’s range.