Sorption - Metal

Hi,

I was wondering how I may simulate a sorption in Co or Ni with Hydrogen; Do I need to use standalone structure or attach the element to something else and minimize it. How about impurities in nanotubes as Fe or Ni, is there  a way to attacheh them to nanotube and look into the changes? I tried multiple ways to use stand alone atom or connected to the tube but failed. Any help and or example would be appreciated.

Sincerely,

Mahdi