There is Nothing Anomalous about 'Anomalous' Underscreening in Concentrated Electrolytes

Over the last decade, experimental measurements of electrostatic screening lengths in concentrated electrolytes have exceeded theoretical predictions by orders of magnitude. This disagreement has led to a paradigm in which such screening lengths are referred to as 'anomalous underscreening', while moderate screening lengths - predominantly those predicted by theory and molecular simulation - are referred to as 'normal underscreening'. Herein we use discrete Fourier analysis of the radial charge density obtained from molecular dynamics simulations to confirm the presence of many electrostatic screening modes present at any one time. We present a new approach for extracting screening lengths directly from the bulk charge density that reveals the origins of both normal and anomalous underscreening. These results reconcile a decades-old disagreement between experimental measurements and theoretical predictions of screening lengths in concentrated electrolytes.