optimizing subset in a supermolecule in G98



Dear CCL-ers,

I want to perform a geom. optz. calculation for a monomer in a trimer supermolecule system maintaining the trimer starting structure (which is coming from x-ray study). Could you tell me some hint about how to perform it? Any suggestion will be helpful. Thank you in advance.
Sorry, I forget to mention that I am using G98 in my previous message.
 


Best regards,
 tarek