Cell Link

Set here the parameters to build a Random Close Packing (RCP) structure.

Radius, Number

To build a RCP structure, a fixed number of atoms is randomly allocated in the Cell volume and then the closest atoms are sucessively moved apart until the minimum atom-atom distance converges to a suitable value, the final hard-sphere diameter, used to determine the volume density and the radius for all atoms (Jodrey algorithm).

By default, GAMGI calculates the number of atoms to allocate such that the final atoms and the template atom will have approximately the same radius. The radius are not exactly the same because the number of atoms must be an integer and the final radius depends of the random sequence and of the relaxation time, but the approximation is close, particularly for larger cell volumes (with more atoms).

Clicking on Number, users can set in the enabled entry the number of atoms to create. These atoms and the template atom will have different radius.

When the Cell volume (in Radius mode) or the number of atoms (in Number mode) is too small, an error is shown.


The relaxation time controls the dynamics of the convergence process. Typically, increasing 10 times the relaxation time, increases 10 times the processing time and increases slightly the density, in the range 0.62-0.64 (the atoms have more time to find better positions).


Initially atoms are randomly allocated using a sequence of (pseudo) random numbers, generated from a Seed initiator. Using different seeds, different random sequences and final results will be produced. Using the same seed, the same results will be obtained.