Atom overview

Atom is the continuum material solver. It uses the Moving Least Squares Material Point Method (MLS-MPM) on the GPU. Particles carry the material, and a background grid resolves collisions and pressure, so one solver handles sand piles, wobbling jelly, flowing mud, molten lava and breaking concrete.

The quickest start is an Atom template: Sand Bulldozer, Jelly Stairs, Mudslide or Sand Dust.

The graph

Emitter ───────┐
Atom material ─┤
Forces ────────┼─► Atom Solver ─► (Surface / Instance Mesher) ─► Simulation Output
Colliders ─────┤
Multiphase ────┘

Node	Purpose
Particle Emitter or Mesh Emitter	Where the material starts.
Atom material	What the particles are made of. See Materials.
Forces	Gravity, wind, drag, buoyancy, vortex, turbulence, attractor, curve and explosion.
Colliders	Object Collider, Ground Plane and Kill Volume.
Atom Multiphase	Interaction between materials. See Wetting, melting and multiphase.
Particle Wrangle	Your own per-particle code. See Wrangles.
Atom Solver	Runs the simulation.
Surface Mesher or Instance Mesher	Draw the particles as a liquid surface or as instanced grains.

Atom Solver settings

Setting	Default	What it does
Mode	Explicit	Explicit is accurate and crisp. Position-Based is 3 to 4 times faster at few substeps but softer.
Resolution	Grid	Whether the grid is set directly or from the particle separation.
Grid	64	Background grid cells across the domain. Up to 256 the grid is dense, which is fastest. Above that, a sparse grid allocates only cells the material occupies.
Particle Separation (m)	0.01	Spacing of the particles a volume is filled with. The grid cell is twice this.
Max Particles	1,000,000	Particle capacity. Allocated in tiers of 250,000, 1 million and 4 million.
Domain Scale (m)	2	Edge of the cubic domain. At the same grid resolution, a larger domain is coarser.
Domain Object	none	Position of the domain’s centre. Unset keeps it centred on the origin, floor-aligned.
Domain Walls	Slip	How particles behave at the domain’s edges.
Seed	0	Random seed. The same seed reruns bit-identically.
Export Deformation	off	Caches each particle’s deformation gradient and plastic state for rendering and the GPU mesher. Adds 44 bytes per particle per frame.
Debris Points	off	Emits a point wherever material breaks, for secondary debris instancing.
Sleeping	off	Particles that stay slow for a while stop integrating until the material around them moves.

See Time and stability for substeps, CFL and the time scale. Every setting is in the Solver reference.

Note

The Atom grid cannot place particles within a few cells of its walls. Templates keep their domain floor-aligned and start blocks a little above the floor for this reason. If your material seems to start in the wrong place, check that the emitter is inside the domain.

Drawing the result

Output mode	Use for
Points	A fast, accurate preview.
Instances	Sand and gravel as instanced grains.
Surface	Liquids and lava as a mesh. See Surface meshing.

With sand or snow drawn as points, Micro-Grains renders several small grains per particle.

Colour modes in the viewport

Uniform, Velocity, Material, Temperature, Damage, Emitter and Wetness. Pick one in Viewport Display.