Tommi, Is there a elegant way to add silicon parameters for the Tripos engine? I know there are a few other atoms that are just using "approximations" basically Hydrogen values. -Donald ----- Forwarded message from Sean Nedd <sean at si.fi.ameslab.gov> ----- We have been using the Tripos5.2 method form some MM calculations with an emphasis on Siloxane systems. I have been getting erroneous bond lengths for Si-C and Si-O bonds as can be seen in the input file attached. ----- End forwarded message -----