Some questions about fixregGL and fixSL in the config file ps_config.xml

1、The fixregGL region mentioned in the ps_config.xml configuration file in your code is a fixed atomic region for each subdomain, but shouldn't the simulation emulate all the atoms? Why do you need to fix some regions of atoms about:

#Define the region where atoms are fixed in every SLD:
region **fixregGL  **block 0.0 100.0 0.0 100.0 0.0 6.5

2、The fixSL parameter in the program is determined according to what.

<!-- Execute this every time new atoms are passed into the Engine -->
<PostInitScript>
group fixGL region fixregGL
#Note - **SLParSplice will define fixSL**
group mobile subtract all fixGL fixSL
fix freeze1 fixGL setforce 0.0 0.0 0.0
fix freeze2 fixSL setforce 0.0 0.0 0.0
velocity    fixGL set 0.0 0.0 0.0
velocity    fixSL set 0.0 0.0 0.0
</PostInitScript>

3、As for the Ag atom in the example, is this program only suitable for metals or crystals? Whether the performance is as good in non-metallic or non-crystalline.