How does GMSH adopt PML boundary absorption

Hi there ,
I am trying to use GMSH for partition,
here,I did it this way,python LibGmsh2Specfem_convert_Gmsh_to_Specfem2D_official.py test.msh -t F -l A -b A -r A
but the boundary reflection is a bit obvious, I see that PML boundary conditions can be used in the script, so how can I use PML boundary absorption when applying to the script ,LibGmsh2Specfem_convert_Gmsh_to_Specfem2D_official.py?

Thanks very much.

zhang