BZ

Do not attempt to add keyword BZ.  Use the utility program MAKPOL with keyword "LET" - that will make a data set in the correct format.

In order for BZ to work, certain specific conditions must be satisfied, these are:

1. The data set must consist of a set of fundamental unit cells, in a specific order.  For a solid, the order of unit cells is (0,0,0), (1,0,0), (2,0,0), ... (0,1,0), (1,1,0), ... (0,0,1), (1,0,1), ...(0,1,1), (1,1,1), ... (n,l,m).  Within each unit cell, the order of the atoms must be exactly the same.  Because these conditions make writing the data set very difficult, the utility program MAKPOL should always be used to create the data set.  MAKPOL is normally used for generating data sets for modeling the chemistry of solids, mainly organic systems, so the default in MAKPOL is for the data set to consist of entire molecules.  For band-structure work, an extra keyword "LET" must be added; this suppresses the operation that generates entire molecules, and instead makes a data set suitable for use with BZ.
    
2. When "LET" is present, only the atoms that make up the unit cell should be present.  The unit cell must also be stoichiometric, that is, there must be an exact integer multiple of the formula present.  For example, TiO₂ in the rutile structure has a unit cell with one titanium atom at a vertex and one at the center of the tetragonal unit cell.   There must also be four oxygen atoms, two inside the unit cell and two on the surface of the unit cell.
    
3. Keyword MERS must be present.  This is written out when MAKPOL is run, and it should not be edited or deleted. 
    
4. The Large Unit Cell (LUC) used must be sufficiently large that all phenomena relating to solid-state effects would not change if the LUC was increased in size.  This condition is normally satisfied if the LUC could hold a sphere of diameter 9 Ångstroms.  For narrow band gap solids (the semiconductors) and true metals, the LUC might need to be larger, for example big enough to hold a sphere of diameter 10 or 11 Ångstroms.
    
5. The geometry should not be modified after MAKPOL is run.  This means that if geometry optimization is run, the optimized geometry should then be used in constructing a new data set for MAKPOL.

Two types of file can be generated by BZ: electronic band structure files and phonon band structure files.  If an electronic band structure is needed, then at least one SCF calculation must be run, and a normal output must be generated, i.e., an output that includes the line "FINAL HEAT OF FORMATION"  If a phonon band structure is needed, then a FORCE calculation must be run.  This calculation normally takes a long time to run, so a useful strategy is to write out the force matrix (using ISOTOPE) as an insurance in case anything goes wrong.  If something does go wrong, then correct the error and use RESTART to re-run the end of the job.

To summarize, for an electronic band structure calculation, use keywords BZ MERS=(n₁,n₂,n₃) and possibly 1SCF, together with a data set generated by the program MAKPOL.  For a phonon band structure calculation, use keywords BZ MERS=(n₁,n₂,n₃) FORCE and possibly RESTART,