For POTential=SOFTsquare, the square-well function is used for
distances within a specified ``switching" region (
, specified
by the RSWITch statement), whereas outside this region a ``soft"
asymptote is used:
where 
is given by Eq. 18.9 and
a and b are determined by the program such that 
is a smooth function at the point 
.
The
slope of the asymptote c is specified by the ASYMptote statement,
is specified by the RSWItch statement, and the
exponent softexp is specified
by the SOEXponent statement.
The distance R is defined in Section 18.2.
