interfragment polyatomic linears

[psi-rking]

Debug, check, test if interfragment optimizations work for linear molecules. Note that detection of linearity must lead to the omission of some coordinates, so that a full optimization might not occur. So if the user desires a final non-linear structure, it would be better to either 1) start with a bent structure; or 2) use a supermolecule approach.

Good tests would be acetylene dimer, and acetylene+water.