A question about lj/expand potential

In my simulation system, around a large nanoparticle there is homogenerous polymer in my initial configuration.
As you can see in the picture attached below, there is a extra shell around the nanopaticle. The radius of this extra shell
coresponds to the position of traslational potential well depth.(blue curve is original and orange is truncated and shifted lj/expand potential)

What i expect is that i just want to reserve right side of potential function because the left side of potential actually make no
science sense.
What i should do to shield this?