# Perspective: Configurational entropy of glass-forming liquids

## TL;DR

This paper reviews the importance, challenges, and recent computational advances in measuring the configurational entropy of glass-forming liquids, highlighting its role in understanding the glass transition.

## Contribution

It provides a pedagogical overview of the configurational entropy, discusses measurement difficulties, and critically reviews computational methods for its accurate determination.

## Key findings

- Simulations enable precise measurements of configurational entropy.
- Computational tools offer non-ambiguous, experimentally relevant data.
- The perspective bridges experimental and theoretical approaches in glass physics.

## Abstract

The configurational entropy is one of the most important thermodynamic quantities characterizing supercooled liquids approaching the glass transition. Despite decades of experimental, theoretical, and computational investigation, a widely accepted definition of the configurational entropy is missing, its quantitative characterization remains fraud with difficulties, misconceptions and paradoxes, and its physical relevance is vividly debated. Motivated by recent computational progress, we offer a pedagogical perspective on the configurational entropy in glass-forming liquids. We first explain why the configurational entropy has become a key quantity to describe glassy materials, from early empirical observations to modern theoretical treatments. We explain why practical measurements necessarily require approximations that make its physical interpretation delicate. We then demonstrate that computer simulations have become an invaluable tool to obtain precise, non-ambiguous, and experimentally-relevant measurements of the configurational entropy. We describe a panel of available computational tools, offering for each method a critical discussion. This perspective should be useful to both experimentalists and theoreticians interested in glassy materials and complex systems.