The BoxExternal interaction implements a repulsive 9-3 confining potential along the walls of an orthorhombic box, in all three directions. For each Cartesian direction i=0, 1, or 2 for which the box dimension is L[i], the interaction creates a repulsive potential centered around x[i] = 0 or x = L[i], thus confining x[i] to the domain 0 < x[i] < L[i]. The form of the potential in each direction is the same as that used in the one-dimensional SliExternal potential, which confines particles only in the z (i=2) direction.
The parameter file format is the same as for BoxExternal:
epsilon float
sigma float
cutoff float
As in BoxExternal, the parameter 
has a hard-coded default value of 
.
