I have a rather general question of what software packages exist to do Quantum Theory Atom in Molecule (QTAIM) analysis of periodic and non-periodic systems. Working with Gaussian I have previously used Multiwfn. What other codes exist and what advantages/disadvantages do they have?
critic2 is a very nice QTAIM code that supports interfaces to many codes, including also periodic systems: "WIEN2k, elk, PI, Quantum ESPRESSO, abinit, VASP, DFTB+, Gaussian, psi4, siesta, and to any other program capable of writing the scalar field of interest to a grid"
From personal experience, critic2 is very straight forward to compile and the developer is responsive to any issues, so definitely recommended!
Purely to calculate Bader charge basins, the Henkelman Bader tool is also very fast and reliable for specifically gridded data (VASP CHGCAR or Gaussian CUBE).
There is also a newer tool called TopoMS that promises improved robustness and has some compelling case-studies in its paper.
"QTAIM" itself is a broad topic, for example I'm not aware which tools currently available might be able to access information about, for example, bond bundles or other features.
Multiwfn is a QTAIM package which supports most quantum chemistry codes, seemingly focusing on non-periodic systems. For example, from a formatted Gaussian checkpoint file it is capable of calculating cube files of properties such as the electrostatic potential or electron localization function. These properties can then be used for many advanced uses of which I have only personally explored a few in a recent article I worked on.
- Critical point analysis of electron density: Identify bonds and lone pairs which exist in a molecule
- Charge analysis of electron density: Identify partial oxidation states arising from polarized bonds or from charge transfer in complexes
- Noncovalent interaction analysis (NCI): Identify where weak interaction/bonding is occurring as well as where steric effects are taking place within the molecule
- Interaction Region Indicator (IRI) / Density Overlap Regions Indicator (DORI) analysis: Similar to NCI analysis but strong chemical bonding can also be visually seen.
- Electrostatic potential analysis: Identify local maxima and minima on an isosurface of electrostatic potential. This allows for accurate quantification of the isosurface, compared to just visual identification.