# Expand selection

This modifier expands an existing particle selection by selecting additional particles that are neighbors of already selected particles. You can choose between four different modes:

> 1. Cutoff: A distance threshold can be specified to select all particles that are within range of an already selected particle.

> 2. Nearest: Selects those particles that are among the N nearest neighbors of an already selected particle. The number N is adjustable.

> 3. Bonded: Extends the selection to particles connected by a bond to at least one already selected particle.

> 4. Molecule: Expands the selection to all particles that belong to the same molecule(s) as already selected particles. In other words, one selected atom in a molecule is sufficient to select the entire molecule.

## Parameters

Cutoff distance

  A particle will be selected if it is within this distance of an already selected particle.

N

  The number of nearest neighbors to select around each already selected particle. The modifier sorts the neighbor list of already selected particles by ascending distance and selects the leading N entries from the neighbor list.

Number of iterations

  This parameter allows you to expand the selection in multiple recursive steps. For example, setting this parameter to a value of 2 will expand the current selection to the second shell of neighbors, i.e., as if the modifier had been applied twice.

See also

`ovito.modifiers.ExpandSelectionModifier` (Python API)