I was calculating MSD and RDF between some specific atoms in a trajectory, I follow these steps to achieve this task:

    (1) Define a set. Draw a structure unit in a .xsd file→ Find patterns based on "ElementType"and then click "new sets".

    (2) Choose a set. Edit sets→“select”.

    (3) Run Forcite→Analysis→MSD or RDF. Then a messagebox appeared,"there are no particles to work on"

There must be something wrong with my operation, can someone help me to solve this problem?