**Syntax:**

probability style value

maxvalue = Pmax = fraction between 0.0 and 1.0diffvalue = M = multiplier on sum of diffusive distances

**Examples:**

probability max 0.5 probability diff 1.5

**Description:**

Set parameters that determine how binary reactions are computed for spatial simulations. A binary reaction occurs in a timestep with a probability P when a pair of reactant particles are within a cutoff distance R.

The *max* style uses the specifed Pmax to set one distance R for all
reactions so that the fastest reaction (maximum rate constant) will
occur with probability Pmax and give the desired k for a well-mixed
system with diffusion-limited reactions. Since other reactions happen
less frequently (smaller rate constants) their P values are set
smaller than the specified Pmax.

The *diff* style sets a distance R for each reaction based on the
diffusion coefficients of its 2 reactants. The sum of the root-mean
squared value for each reactant is multipled by the specified M factor
to compute R. The P for each reaction is then set so that each
reaction happens at the desired frequency for a well-mixed system with
diffusion-limitd reactions.

Note that values of P and R for individual reactions can be overridden via the react_modify command.

**Restrictions:**

This command can only be used for spatial simulations.

**Related commands:** none

**Default:**

max 0.5