Coordination analysis

This modifier performs two computations:

Element-wise RDFs

The Compute partial RDFs option lets the modifier compute separate radial distribution functions for all pair-wise combinations of particle types or chemical elements. The computed partial RDFs will be normalized such that the summation of the partial RDFs, weighted by the product of the two corresponding elemental concentrations, yields the total RDF. For example, for a binary system with two particle species ɑ and β, the modifier computes a set of three partials functions gɑɑ, gɑβ and gββ, which add up to the total distribution as follows:

g(r) = cɑ2 gɑɑ(r) + 2 cɑcβ gɑβ(r) + cβ2 gββ(r)

Here, the cɑ and cβ denote the concentrations of the two species in the system and the factor 2 in the mixed term appears due to gɑβ(r) and gβɑ(r) being always identical.

Time-averaged RDF

Note that the Coordination analysis modifier calculates the instantaneous RDF for the current simulation frame only and outputs it as a data table that varies with simulation time. Subsequently, you can use the Time averaging modifier of OVITO to reduce all per-frame RDFs to one mean RDF, averaging over all frames of the loaded trajectory.

Bond length distribution

Furthermore, OVITO provides another analysis tool for computing the bond length distribution specifically for bonded pairs of particles: the Bond analysis modifier. This modifier can additionally compute the distribution of bond angles formed by triplets of particles.

See also

CoordinationAnalysisModifier (Python API) pro