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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsSELF (Steric Exclusion Localization Function) is a quantum-mechanical method for quantifying and locating steric repulsion in molecules. Rather than reducing steric effects to one overall number, it maps where repulsion occurs in three dimensions and can examine interactions between fragments within a single molecule as well as between molecules.
What SELF measures
Steric effects are often used to explain molecular shapes and reaction outcomes, but the term can describe more than one physical contribution. SELF’s authors frame steric repulsion in terms of the Pauli principle: the kinetic-energy cost associated with same-spin electrons being constrained to occupy the same spatial region.
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The method decomposes a Pauli kinetic-energy-excess density into intra-fragment and inter-fragment contributions. It uses the inter-fragment contribution to represent steric exclusion, then displays SELF values on a surface derived from the Independent Gradient Model (IGM). Colors on the surface indicate the intensity of repulsion. The result is a spatially resolved visualization, not simply a single total steric score. The Chemical Science paper describes the method and its applications.
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How the map differs from a steric number
A scalar descriptor can be useful for comparing systems, but it compresses spatial detail: it does not, by itself, show where an interaction occurs or which fragments contribute. SELF is intended to retain that location information while providing quantitative values. The authors also describe atomic-level decomposition, so a user can inspect contributions at a finer scale than a whole-molecule summary.
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This distinction matters when a molecule has several possible sources of crowding. A map can help distinguish a prominent clash from less obvious interactions elsewhere in the structure. It does not automatically establish which interaction controls a reaction or property; that interpretation still depends on the chemical system and the rest of the evidence.
What the researchers demonstrated
Organocatalytic stereoselectivity
In one organocatalysis example, a reaction’s selectivity had been attributed to clashes between a catalyst’s mesityl group and a p-methoxyphenyl group on the substrate. Chemistry World reports that SELF supported this explanation while also revealing additional, less obvious steric interactions. That is evidence from a particular application, not proof that the method predicts selectivity for catalysts generally. Chemistry World’s report discusses the example.
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Atropisomerism and rotation barriers
The paper also applies SELF to atropisomeric pharmaceutical scaffolds and presents it as suitable for intramolecular steric repulsion, including interactions associated with rotation barriers. This addresses a different question from the familiar picture of two separate molecules approaching: parts of one molecule can crowd each other as a bond rotates.
Éric Hénon, one of the authors, told Chemistry World that earlier approaches were designed for separate molecules approaching one another and that SELF handles intramolecular rotation barriers naturally. This is the researcher’s characterization of the method, rather than an independent comparative benchmark.
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Nickel–phosphine complexes
For Ni(CO)3L phosphine complexes, the paper compares SELF with the established Tolman-angle approach. Chemistry World reports that the results correlated with Tolman angles, while SELF indicated a smaller interaction between the nickel center and ligand than the Tolman analysis suggested. This single case does not show that SELF universally replaces Tolman angles.
SELF and other ways to assess steric effects
The authors position SELF against two broad kinds of approach: geometric descriptors based on fixed-size hard spheres, and methods that report energies without the same spatial localization. Their argument is that these approaches can be less specific about where repulsion occurs and which atoms participate. That is the paper’s rationale for SELF, not an independent ranking of all steric-analysis methods.
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| Comparison question | Why it matters |
|---|---|
| Quantum-mechanical or geometric? | Clarifies whether the descriptor is based on an electronic-structure calculation or a geometric model. |
| Aggregate value or spatial map? | Shows whether the result summarizes a system or identifies where repulsion is localized. |
| Atom or fragment resolution? | Indicates how specifically the result can attribute contributions. |
| Intermolecular, intramolecular, or both? | Tests whether the method can address crowding within one molecule as well as between separate species. |
| What calculation is required? | The SELF paper says its input can be a single electronic-structure calculation on the complete system; practical suitability still depends on the system being studied. |
| Is it validated for this chemistry? | A published demonstration in one setting does not establish performance in every catalyst, ligand, or molecule. |
What is known about implementation
The method is implemented in IGMPlot. The study reports using version 3.17, and its data-availability statement points to the code online. That version number describes the software used in the paper; current availability, installation requirements, supported platforms, and the latest version are not established by the article. The paper’s data-availability statement is the source for the implementation information.
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The primary paper by Guillaume Hénon Just, Corentin Lefebvre, Akilan Rajamani, Hassan Khartabil, Julien Pilmé, and Éric Hénon was first published on 9 January 2026 in Chemical Science, volume 17, pages 5394–5403, DOI 10.1039/D5SC07952G. It is open access. Read the paper for the method’s definitions and system-specific calculations.
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Promise and practical limits
SELF’s strongest practical distinction is that it aims to combine a quantitative description with a visual account of where steric exclusion occurs, including within a molecule. The examples span organocatalysis, atropisomerism, and nickel–phosphine coordination chemistry, but they are demonstrations rather than evidence of universal predictive performance.
In Chemistry World, computational organic chemist Robert Paton described the approach as moving toward a more correct picture of sterics because it creates a steric map rather than providing only an energy value. Natalie Fey, a computational organometallic chemistry researcher at the University of Bristol, welcomed its theoretical rigor and visualization while cautioning that Tolman parameters are well established and that adoption may take time. Whether SELF adds practical value for a given problem therefore depends on the system, the question being asked, and how its output complements established analyses.
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