6.1 Database

The database contains standard basis sets (and fit sets, frozen core orbitals) for all chemical elements of the periodic table at different levels of accuracy. The database is partitioned in subdirectories. Some of these are special: the subdirectory Dirac contains input files for the program dirac (computation of relativistic potentials and charge densities). Most subdirectories contain files for the create runs: subdirectories SZ through TZ2P.

The names of the files in the database consist of two parts: the standard symbol for the chemical element and the level of frozen core approximation. Mn.2p for instance is a data file for Manganese with a frozen core up to and including the 2p shell.

Polarization functions are not provided for all elements because our experience with them is limited. If you contemplate to compile more extended basis sets, by including one or more polarization functions, a good rule of thumb to choose the functional characteristics, is the following. Take the next higher l-value that does not yet occur in the function set (however, do not go beyond f-functions: the program cannot (yet) handle g-type basis functions), select the minimum value for the main quantum number n that is compatible with the l-value (i.e.: 2p, 3d, 4f), and determine the exponential decay factor such that the function attains its maximum value at somewhere between 1/3 and 1/2 times the bond length; the functional maximum for a Slater-type exponential function is at R=(n-1)/ a.

A few all-electron basis are included in the data base. In addition, some all-electron sets are provided in the subdirectory Special/ae of the database. However, the files in Special/AE do NOT contain fit functions so they cannot be used directly in Create runs. Fit functions for the all-electron basis sets must include more, in particular more contracted functions that the standard fit sets that are provided in the normal database files. If you would combine the all-electron basis set with an inadequate fit set the results are unreliable and absolutely in adequate, in the same fashion as when you would have used a highly inadequate basis set.