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SELF (Steric Exclusion Localization Function) is a quantum-mechanical method for mapping where steric repulsion occurs in a molecule or between molecular fragments. Instead of reducing steric effects to one overall number, it visualizes their location and intensity, with the potential for atomic-level analysis. The method is implemented in IGMPlot; the study introducing it used version 3.17.
What SELF measures
Steric effects are commonly used to explain molecular shapes, reaction selectivity and barriers to rotation. SELF gives that idea a spatial description grounded in Pauli repulsion: the kinetic-energy cost associated with same-spin electrons being constrained to occupy the same region of space.
The method decomposes a Pauli kinetic-energy-excess density into contributions within fragments and between fragments. SELF uses the inter-fragment contribution to describe steric exclusion. Its values are displayed on a surface derived from the Independent Gradient Model (IGM), with color indicating the intensity of repulsion. The result is a map of where the interaction occurs, rather than only a single aggregate steric parameter.
How the visualization is produced
The authors describe SELF as using a single electronic-structure calculation on the complete system as its input. The resulting map can be decomposed at the atomic level and applied to fragments within one molecule as well as to separate molecules. In this context, “quantitative” means that the map encodes calculated values; it does not imply one universal score or a validated prediction for every chemical system.
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SELF is implemented in IGMPlot. The paper reports using version 3.17, and its data-availability statement points to the code online. Current software versions, installation requirements and supported operating systems are not established by the paper. The open-access paper was published in Chemical Science on 9 January 2026 (volume 17, pages 5394–5403).
What the paper demonstrates
Organocatalysis and stereoselectivity
One application examines a reaction whose selectivity had been attributed to a clash between a catalyst’s mesityl group and a substrate’s p-methoxyphenyl group. Chemistry World reports that SELF supported this explanation while also showing less obvious steric interactions. This is evidence for how the method can analyze a particular case, not proof that it predicts selectivity in all organocatalytic reactions. Chemistry World’s report was published on 5 February 2026.
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Atropisomerism and rotation barriers
The researchers also apply SELF to atropisomerism in pharmaceutical scaffolds and describe its use for intramolecular steric effects, including those associated with rotation barriers. That matters because a method designed only for two molecules approaching one another may not represent interactions within a single molecule in the same way. Éric Hénon, one of the researchers, characterized this intramolecular use as a new opportunity; that is the author’s view, not an independent comparative benchmark.
Nickel–phosphine complexes
For Ni(CO)3L phosphine complexes, the paper compares SELF with Tolman angles, a familiar geometric descriptor in organometallic chemistry. Chemistry World reports that the results correlated with Tolman angles but indicated a smaller interaction between the nickel center and ligand than Tolman analysis suggested. A result from this application does not establish that SELF universally replaces or outperforms Tolman angles.
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How SELF differs from other steric descriptors
The paper’s rationale is that common approaches answer different questions. Geometric descriptors such as hard-sphere models represent steric demand through fixed-size shapes or angles; energy-based methods can quantify energetic effects without necessarily showing where they arise. SELF is intended to retain spatial information about the location of repulsion and the atoms or fragments involved. These are the authors’ framing and should not be read as a universal ranking of methods.
| Comparison question | SELF | Other descriptors or methods |
|---|---|---|
| Basis | Quantum-mechanical calculation of Pauli-related steric repulsion | May use geometric descriptors or energy-based analyses; the basis depends on the method |
| Output | Spatial map with quantitative values | May provide an aggregate number, geometry-based measure or energy decomposition |
| Localization | Designed to show where repulsion occurs, with atomic-level decomposition | Spatial and atomic detail vary by method |
| Intramolecular use | Demonstrated and described for effects such as rotation barriers | Some established approaches were designed primarily for interactions between separate molecules |
| Validation | Demonstrated on selected model and chemically relevant systems | Depends on the descriptor and the specific system |
When choosing a descriptor for a real problem, check whether it is quantum-mechanical or geometric, whether it reports a total value or locates the interaction, whether it resolves atoms or fragments, whether it treats intramolecular effects, what inputs it needs, and whether it has been validated for the chemistry at hand.
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What the results do—and do not—establish
SELF offers a way to inspect steric repulsion that combines calculated values with a visual map. The published examples cover organocatalytic stereoselectivity, atropisomerism and nickel–phosphine complexes, but they do not establish broad predictive performance across catalysts, ligands or molecules. The paper’s claims about input requirements and decomposition describe the method; they are not an independent benchmark across all chemistry applications.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchIn Chemistry World, computational organic chemist Robert Paton called the method a move toward a more correct picture of sterics because it produces a map rather than only an energy value. Computational organometallic chemist Natalie Fey welcomed its theoretical rigor and visualization while noting that Tolman parameters are well established and that adoption may take time. Those comments reflect expert responses to a new method, not a settled consensus about when it should replace existing descriptors.
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When SELF may be useful
- Use it when the question is not only how large a steric effect is, but where it arises in a molecular system.
- Consider it for intramolecular questions, such as possible steric contributions to a rotation barrier, as well as interactions between separate fragments.
- Interpret its maps alongside established descriptors and chemical evidence when working in areas where those measures are customary.
- Check that the calculation and decomposition are appropriate for the particular molecule and research question; the published examples do not validate every possible application.
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