Setting up an Input File

We now give a brief guide to set up input.

You first specify the minimally required information: the geometric structure and the definition of the atoms (positions and function sets) that constitute the system. Then you add keys for all aspects for which you don't want to use the defaults.

1. Specify a title using the key Title.
2. Define the structure of periodicity with the key Lattice.
3. Give the positions of the atoms with the key Atoms.
   All atoms specified in the corresponding data block belong to one type of atom.
   Consequently, the key Atoms must be repeated as many times
   as there are different types of atoms. Different chemical elements necessarily belong to
   different types. The reverse is not true: it is allowed to define more than one 'type' of
   Carbon atom, for instance to equip them with different basis sets.
4. Specify the BasisDefaults key. With this you can set the quality
   of the basis set to be used, and the size of the frozen core. Given your settings the program will
   look up an appropriate basis set for each type from the database. This replaces the old style AtomType
   key that needed to be specified for each type.
5. Add further keys for features you don't want to be defaulted, for instance
   Unrestricted (if you want to do a spin-unrestricted calculation),
   Accuracy (general precision parameter),
   KSpace (parameter for numerical integration over the Brillouin Zone),
   DOS (generation of the density-of-states), and so on.
6. Terminate the input file by typing End Input
7. Comments: everything behind a exclamation mark "!" is treated as comment. If you put it behind a
   key, leave some space between it, otherwise it will be seen as part of the key.

Consult the sample runs and description below, to see how you may use the various keys (Lattice, Atoms, BasisDefaults).