For POTEntial=SQUAre-well, a square-well function is used:
where 
is defined as
S is the scale factor specified by the SCALe statement, C is the scale
factor specified by the SQCOnstant statement, and d, 
, and
are specified by the ASSIGn statement:
The exponent exp is specified by
the SQEXponent statement and
is specified by the SQOFfset value.
The distance R is defined in Section 18.2.
