A Practicable Measure and Spatial Visualization of Steric repulsion with Atomic Resolution

Steric repulsion, often regarded as a macroscopic manifestation of the Pauli exclusion principle, which prevents electrons with the same spin from occupying the same space, is experiencing renewed interest across the field of chemistry. While its importance is widely recognized, visualizing where and how it occurs remains challenging. We introduce the Steric Exclusion Localization Function (SELF), a novel tool that reveals steric interactions in three dimensions, requiring only a single quantum calculation. With SELF, chemists can see exactly where steric clashes happen in their molecules, quantify their magnitude, and identify which atoms contribute mostly to them. SELF transforms abstract quantum mechanical concepts into intuitive 3D maps accessible through the user-friendly IGMPlot software. We demonstrate its power across diverse chemical systems: from understanding atropisomerism in pharmaceutical scaffolds to rationalizing selectivity in catalysis. Unlike traditional quantum mechanical methods that yield only numbers, SELF provides visual insights that organic chemists can immediately interpret and apply. This approach bridges the gap between theory and practical chemical understanding, making sophisticated quantum mechanical analysis accessible to the broader chemical community. We hope this tool will prove valuable for chemical design, research applications, and teaching steric effects.