What Analyses and Visualizations Does Chemissian Offer?

Chemissian is a desktop tool for analyzing the electronic structure and spectra of molecules, and it produces publication-ready figures in five main areas: molecular orbital (MO) energy-level diagrams, MO contribution diagrams, UV-Visible spectra overlaid with experimental data, electronic and spin density maps, and population/valence results. It works by reading output files from quantum chemistry packages such as Gaussian, GAMESS/US-Gamess, Firefly/PC-Gamess, Q-Chem, Molpro, NWChem, ORCA, Turbomole, and Spartan, so the analyses you can run depend on what data those outputs contain (for example, TDDFT or CIS results are needed for spectra).

Molecular orbital energy-level diagrams

Chemissian builds MO diagrams from both Hartree-Fock and Kohn-Sham calculations. The diagram is not just a static plot: an integrated graphical editor lets you add text labels, draw connecting lines between energy levels, and "occupy" levels with electrons. You can move between energy levels with the keyboard or mouse cursor to inspect each one, which makes the diagrams suitable for explaining bonding and electronic structure in a paper or presentation.

Contribution diagrams

For any selected MO, Chemissian shows how much each atomic or molecular fragment contributes. This appears either as a separate contribution diagram or directly on the MO diagram. This is the feature to use when you need to argue that a particular orbital is localized on one fragment or delocalized across the molecule.

UV-Visible spectra

Chemissian includes a graphical analyzer for electronic spectra. Load an output file containing TDDFT or CIS data from GAMESS, Firefly, Gaussian, Spartan, Q-Chem, NWChem, or ORCA, and the spectrum is displayed. Calculated and experimental UV-VIS spectra can be plotted on the same chart, which supports assigning observed bands to computed transitions and studying the nature of those transitions.

Electronic and spin density maps

The software calculates and visualizes electronic density and spin density, and prepares the images for publication. It also handles spin natural orbitals and natural transition orbitals, which are useful for describing excited states and open-shell systems in a compact orbital picture.

Populations and valences

Chemissian calculates populations and valences, giving quantitative backing to the orbital pictures above — for example, when you want to compare charge distribution or bonding character across a series of molecules.

Practical notes before you start

• Check your output type first. Spectra require TDDFT/CIS data in the output; MO diagrams require the orbital energies and coefficients that the supported packages write by default.
• Confirm package support. The site lists Gaussian, US-Gamess, Firefly/PC-Gamess, Q-Chem, Molpro, NWChem, ORCA, Turbomole, and Spartan, but the spectra section names a slightly narrower set (GAMESS, Firefly, Gaussian, Spartan, Q-Chem, NWChem, ORCA). If you use Molpro or Turbomole, verify that the specific analysis you need is available.
• Plan for figure editing. Labels, connecting lines, and electron occupancy are added inside Chemissian, so you can finish diagrams there rather than exporting to a separate drawing tool.

The site provides a download page, an order page, and online help; pricing and licensing terms are not stated in the material reviewed here, so check the Order page directly if cost matters for your decision.