I note that Silicon calculations using Ghemical result in high steric energies (ie 393 kJ for tetramethylsilane) and absurd C-Si bond lengths, ie 0.12 nm. I think there is clearly an error in the force field parameters for this element. Can anyone confirm this? -- Henry Rzepa. +44 (020) 7594 5774 (Voice); +44 (0870) 132 3747 (eFax); rzepahs at mac.com (iChat) http://www.ch.ic.ac.uk/rzepa/ Dept. Chemistry, Imperial College London, SW7 2AZ, UK. (Voracious anti-spam filter in operation for received email. If expected reply not received, please phone/fax).