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. Type in a title: the first line of input.
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. For each of the types defined by the ATOMS keys (and in the same order) do:
5. Define the numerical (Herman-Skillman-type) spherically symmetric free atom: (block-type) key DIRAC.
6. Add (optionally) Slater-type basis functions; key: BASISFUNCTIONS.
7. Supply fit functions (used for evaluation of the Coulomb potential from the charge density); key: FITFUNCTIONS.
8. Add further keys for features you don't want to be defaulted, for instance SPIN (if you want to do a spin-unrestricted calculation), ACCINT (precision parameter for numerical integration in real space), KSPACE (parameter for numerical integration over the Brillouin Zone), DOS (generation of the density-of-states), and so on.
9. Terminate the input file by typing END INPUT

Consult the sample runs and description below, to see how you may use the various keys (LATTICE, ATOMS, DIRAC...).