Drive an IRC session

IrcSession traces the intrinsic reaction coordinate (IRC) on either side of a supplied saddle. IrcKind::Gs2 uses the moving mass-weighted constraint; IrcKind::Morokuma selects the predictor-corrector path. Each call to step performs one outer IRC move.

new accepts a molecular Cartesian packing and atom masses. new_euclidean accepts an arbitrary nonzero dimension with unit coordinate weights. from_surface estimates the launch mode through Hessian actions; a host with a measured mode can pass it to new.

set_direction restores the saddle and reverses the launch. reset clears the approximation at a surface change. The GS2 step rejects an energy increase above its specified numerical threshold and reduces the radius.

Select L2Norm or LinfNorm for a generic vector packing. MaxForceOnAtom groups Cartesian triples. The C interface exposes construction, stepping, position access, direction changes, reset and destruction; tests/c/irc_abi.c exercises both directions and both IRC methods.