1. The problem statement, all variables and given/known data I have a fcc structure, the net parametre is 4.46*10-10m, the potential energy/mol is -1.88kJ/mol. My task is to find the parametres ε and σ of the potential. 2. Relevant equations Φ=-4ε[(σ/r)6+(σ/r)12] 3. The attempt at a solution I can find the value of r using the net paramentre; r=[(√2)/4]*a. If I divide the potential energy/mol by 6.02*1023 I can find the potential energy/atom, but I still have only one equation with both of the parametres to determine. I have to find another equation with one or both paramentres, but I don't know where to find it. All sugestions are appreciated. Thank you very much.