print_usage Subroutine

   subroutine print_usage()
      character(len=256) :: prog_name
      integer :: stat

      call get_command_argument(0, prog_name, status=stat)
      if (stat /= 0) prog_name = "pic_basis_reader"

      print *
      print *, "Usage: ", trim(prog_name), " <geometry.xyz> <basis_name>"
      print *
      print *, "Arguments:"
      print *, "  geometry.xyz   XYZ format molecular geometry file"
      print *, "  basis_name     Name of basis set (e.g., 6-31G, 6-311G**)"
      print *
      print *, "Options:"
      print *, "  -h, --help     Show this help message"
      print *
      print *, "Example:"
      print *, "  ", trim(prog_name), " water.xyz 6-31G"
      print *

   end subroutine print_usage