Where to Download Chemissian and Find Its Documentation

Chemissian is available from its official site, chemissian.com. The site's navigation includes Download, Order, Online Help, FAQ, News and updates, and Contact us pages, so you can get the software and its documentation from the same place. Use the Download page to obtain the program, the Online Help and FAQ pages for usage questions, and the Order page for licensing.

Getting the Software

The site lists a dedicated Download page in its main navigation. That is the entry point for obtaining Chemissian. The site also has an Order page, which indicates that licensing or purchase is handled separately from the download; the available materials do not state prices or whether the download itself is unrestricted, so check both pages before assuming terms.

Documentation and Support

The Online Help page is the main documentation resource, and the FAQ page covers recurring questions. The News and updates page carries current information about the software, which is worth checking when you want to know whether a feature or fix you need has been released.

What the Documentation Covers

Knowing what Chemissian does helps you target the right help page. According to the site, Chemissian analyzes the electronic structure and spectra of molecules. Its documented capabilities include:

• Building molecular orbital energy-level diagrams using Hartree-Fock and Kohn-Sham methods, with a graphical editor for text labels, connecting lines between levels, and placing electrons on levels.
• Comparing calculated and experimental UV-VIS electronic spectra on the same plot.
• Building, visualizing, and interpreting UV-VIS spectra from TDDFT/CIS output.
• Calculating and visualizing spin natural orbitals, natural transition orbitals, and electronic and spin densities, prepared for publication.
• Analyzing electronic density distribution and calculating populations and valences.

If your question concerns one of these tasks, the Online Help page is the place to look first; the FAQ is better suited to setup or recurring-issue questions.

Input Files You Can Bring

A practical check before downloading: Chemissian reads output files from a range of quantum chemistry packages, including Gaussian, US-Gamess, Firefly/PC-Gamess, Q-Chem, Molpro, NWChem, ORCA, Turbomole, and Spartan. The UV-VIS spectrum tools are described for output from GAMESS, Firefly (PC-GAMESS), GAUSSIAN, Spartan, NWChem, Orca, and Q-Chem containing TDDFT/CIS data. Confirm your program is on these lists so the file you plan to load is supported.

A Reasonable First Session

1. Open chemissian.com and go to the Download page to get the software.
2. Install it, then open Online Help and read the sections matching your task, such as MO diagrams or UV-VIS spectra.
3. Load an output file from a supported package that contains the relevant data (for spectra, TDDFT/CIS results).
4. If something behaves unexpectedly, check the FAQ before using Contact us.
5. Check News and updates periodically for changes that affect your workflow.

The main snag to expect is loading a file without the data a feature needs, for example a spectrum tool applied to output with no TDDFT/CIS results. Verifying the calculation type in your output before loading avoids most of these dead ends.