# Unsupervised Classification of Local Clathrate Hydrate Structures

## TL;DR

This paper introduces a new algorithm to classify and analyze the molecular structures of clathrate hydrates, improving understanding of their properties and behavior.

## Contribution

A novel cavity-finder algorithm integrated with DBSCAN enables accurate unsupervised classification of local clathrate hydrate structures.

## Key findings

- The new algorithm successfully identifies coexisting water states in clathrate hydrates.
- It accurately detects hydrate cavities by analyzing molecular rings around voids.
- The method works robustly for structure I CO2 and structure II mixed CH4/Dioxane hydrates.

## Abstract

Quantifying and differentiating
the structural characteristics
of clathrate hydrates at the molecular level is crucial for understanding
the properties that underpin hydrate-based technologies. While useful,
current approaches lack sufficient resolution to discern, e.g., interfacial
and dynamical structures. In this study, we present an algorithm based
on Density-Based Spatial Clustering of Applications with Noise (DBSCAN)
that accurately identifies different water states coexisting within
clathrate hydrates. A key novel component is an effective cavity-finder
algorithm, which provides input to the clustering framework. The new
algorithm detects hydrate cavities by analyzing the number and type
of constituent molecular rings around voids. Integrating the new algorithm
with widely used order parameters (e.g., F3, F4, and F4t) provides
a powerful and accurate tool for analyzing hydrate structures at interfaces
and phase transitions. The performance of the new algorithm is assessed
for structure I (sI) CO2 hydrates and for structure II
(sII) mixed CH4/Dioxane hydrates, demonstrating its robustness
and adaptability across different clathrates. Crucially, the proposed
algorithm enables us to identify partially ordered structures characteristic
of the quasi-liquid layer, thereby capturing interfacial dynamics
and molecular-scale details essential for understanding hydrates under
realistic conditions.