I was trying to get the charges and the topology file for this molecule ($\ce{C28H58O7S8}$). enter image description here

But I get the following error despite using the right number of hydrogens.

Semi-empirical geometry optimisation failed. The most likely cause is that either: (1) the geometry was inappropriate; (2) the number of hydrogen atoms or the net charge was inappropriate. Details: *** FAILURE TO LOCATE STATIONARY POINT, SCF HAS NOT CONVERGED (seems to only fail on step 1)

What does it mean by inappropriate geometry? I have tried to address the steric clashes by flattening the whole polymer from a curled conformation. But both of them result in the same error. However the same structure would process easily without the benzene rings and $\ce{-CH3}$ group in their places. What am I missing?

enter image description here enter image description here


1 Answer 1


Did you want to draw Si instead of S? Sulfur atoms bonded to two oxygens and two carbons, like the ones you have drawn here, are at least very rare, if not non-existent. It makes much better sense if what you want is to calculate the molecule with silicons instead of sulfurs, since that will be a silicone oligomer, which looks much more natural than the molecule you are drawing here. The highly non-conventional electronic structure of the four-coordinate sulfur atoms is probably the cause of the SCF convergence failure.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .