# Density fitting (Zlm Fit)¶

The default density fitting scheme in BAND is the so-called Zlm Fit, described in reference 53. We do not recommend to use the STO Fit anymore.

## Zlm Fit¶

The basic idea behind Zlm Fit can be described as follows: the total electron-density is split into atomic densities (in a similar way as the volume is partitioned for the Becke grid). These atomic densities are then approximated by a combination of radial spline functions and real spherical harmonics (Zlm).

ZlmFit (block-type)

ZlmFit
Quality [Basic|Normal|Good|VeryGood|Excellent]
End

Quality
(Default: Normal) controls the accuracy and quality of fitted properties.

ZlmFit
{AtomDepQuality
Ia1 [basic|normal|good|verygood|excellent]
Ia2 [basic|normal|good|verygood|excellent]
...
SubEnd}
End

AtomDepQuality
One can define a different fit quality for each atom, with input numbers Ia1, Ia2, etc. If an atom is not present in the AtomDepQuality section, the quality defined in the Quality key will be used. Example: Multiresolution illustrates how to use this option.

## Obsolete Method - STO Fit¶

In previous version of BAND this was the default option, which is now replaced by Zlm Fit. It is still used in the context of NMR and OldResponse calculations.