In the optical examples of GEANT4, specifically in the cerenkov.mac file where the LXe geometry is defined, is it possible to change the geometry and material of the scintillator and PMTs from LXe to a different material, such as NaI (sodium iodide)? In the cerenkov.mac file, which is part of the optical examples provided in GEANT4, the geometry and material of the scintillator and PMTs are initially defined as LXe (liquid xenon). However, I would like to modify this to use a different material, such as NaI (sodium iodide). I attempted to make this change by modifying the material definition in the DetectorConstuction.cc file, but encountered errors. How can I successfully make this modification, and how can I resolve any potential issues that arise?