Name: Institut für Theoretische und Angewandte Physik (ITAP) Molecular Dynamics configuration file
Extension: imd
Specification: IMD manual
Visualization programs: OVITO
Atomsk only supports IMD files that are "atom configuration files" (not "distribution files"), and only in ASCII format (i.e. those with "#F A" in the header). In IMD format the total number of atoms is not specified, therefore Atomsk must parse the file a first time to count atoms, then allocate the necessary memory, and then parse the file a second time to load atom positions into memory. As a result the reading of files in this format can be quite slow, especially when the number of atoms is large.
In the IMD format the atom species are not specified and are replaced by IMD atom "types" (0, 1, 2...). Because of technical issues, these "types" are all incremented (type 0 becomes 1, 1 becomes 2, etc.), and Atomsk interprets them as atomic numbers (1=H, 2=He, etc.). These dummy "types" can be replaced with the option -substitute. If velocities are present then Atomsk reads them. No other auxiliary property is supported for now.
When writing IMD files Atomsk automatically replaces the atom species by IMD "types" (0, 1, 2...), for the same reason as above. Alternatively the types can be defined thanks to the option -properties. If atom velocities are defined (e.g. if they were read from a format that supports it) they will be written to the IMD file, otherwise velocities equal to zero will be written.
atomsk my_system.cfg imd
This will read the file my_system.cfg, and convert it to my_system.imd.