When keyword MERS is present, information on a one-dimensional polymer, a two-dimensional layer structure or a full three-dimensional solid is written to a file for use by the band-structure program BZ. The integers n1, n2, and n3 define the number of fundamental unit cells in each dimension in a cluster. For a polymer, only n1, is used, for a layer structure n1 and n2 are used, and all three integers are used for true 3-D solids.
Making a data-set "by hand" that would allow band-structures to be generated is very difficult. Don't do it! However, an option is provided in the utility MAKPOL that writes the MOPAC data-set for band-structure work. Use MAKPOL!
The definition of a 'mer' might be of interest. In a polymer or other extended system, the fundamental repeating unit is the mer. For some simple polymers, such as polyethylene, the mer can also be identified with the monomer, in that both the mer and the monomer have the same formula. In other polymers, the mer is not the same as the monomer--condensation polymers are a good example, where the monomer looses water on forming the polymer. In order to be general, therefore, the unit of a polymer is not the monomer, but instead is the mer.
See also BCC