How to decide, how many times we should optimize the structure. like optimization after creating amorphous polymer chain, optimization after amorphous cell creation, optimization in annealing....etc, should we optimize the geometry in every step, if yes then why it is required. 

I have created semicrystalline polymer and verified its properties like mechanical and thermal after that I used this geometry for the calculation of gas diffusivity using MSD. when I introduced gas atoms into geometry then should I need to optimize the geometry again or not.

can anyone explain the concept of optimization/ any suggestion?

Thankyou.