Why the function "GetAtomPos" doesn't work?

Geant4 Version:11.1.3
Operating System:Ubuntu 22.00.04
Compiler/Version: 11.4.0
CMake Version: 3.26.3

Problem

G4Exception : cry001
issued by: G4CrystalExtension::GetAtomBase()
Atom base for element Si is not registered.

Code

Add the following code into DetectorConstruction.cc in channeling examples

for(auto el : *(Crystal->GetElementVector())) {
    for(auto i : crystalExtension->GetAtomBase(el)->GetPos()) {
        G4cout << "Element: " << el << "X: " << i.x() << "\t Y:" << i.y() << "\t Z: " << G4endl; 
   }
}

How to solve this warning? I want to get the position of some element in the crystal.