  ORBKIT is a toolbox for post-processing electronic structure calculations
based on a highly modular and portable Python architecture. The program allows
computing a multitude of electronic properties of molecular systems on
arbitrary spatial grids from the basis set representation of its electronic
wavefunction, as well as several grid-independent properties. The required data
can be extracted directly from the standard output of a large number of quantum
chemical programs. ORBKIT can be used as a standalone program to determine
standard quantities, for example, the electron density, molecular orbitals, and
derivatives thereof. The cornerstone of ORBKIT is its modular structure. The
existing basic functions can be arranged in an individual way and can be easily
extended by user-written modules to determine any other desired quantities.
ORBKIT offers multiple output formats that can be processed by common
visualization tools (VMD, Molden, etc.). Additionally, ORBKIT possesses
routines to order molecular orbitals computed at different nuclear
configurations according to their electronic character and to interpolate the
wavefunction between these configurations. The program is open-source under
GNU-LGPLv3 license and freely available at
http://sourceforge.net/projects/orbkit/. This article provides an overview of
ORBKIT with particular focus on its capabilities and applicability, and
includes several example calculations.
