Molden

Molden is a general molecular and electronic structure processing program.

Major features

Reads output from the ab initio packages GAMESS, Gaussian, MOLPRO, PySCF and from semi-empirical packages such as MOPAC, and supports a number of other formats.
Displays molecular orbitals or electron density as contour plots or 3D grid plots and output to a number of graphical formats.
Animates reaction paths and molecular vibrations.
A Z-matrix editor.

Molden program has been tested on different platforms, namely Linux, Windows NT, Windows95, Windows2000, WindowsXP, MacOSX, Silicon Graphics IRIX, Sun SunOS and Solaris.
Ambfor, the main force field module of Molden, is an external program that can be initialized from Molden. Ambfor admits protein force field Amber and GAFF. Use of Ambfor is automatic when a protein is studied with Molden. The GAFF force field is used only small molecules. Both Amber and GAFF are based on atomic charges. The differences are largely in computational cost, with GAFF being very expensive.
Molden can read several file formats with crystal information.