Cross-over mechanism of the melting transition in monolayers of alkanes adsorbed on graphite and the universality of energy scaling

TL;DR

This study investigates how the scaling factor influences the melting transition in alkane monolayers on graphite, revealing a non-universal, length-dependent crossover mechanism affecting phase change behavior.

Contribution

It demonstrates for the first time that the scaling factor's value critically impacts melting mechanisms and varies with molecular length, challenging prior assumptions of universality.

Findings

Scaling factor decreases with molecular length

Different melting mechanisms are driven by the scaling factor

The melting transition mechanism is not universal

Abstract

The interplay between the torsional potential energy and the scaling of the 1-4 van der Waals and Coulomb interactions determines the stiffness of flexible molecules. In molecular simulations often ad-hoc values for the scaling factor (SF) are adopted without adequate justification. In this letter we demonstrate for the first time that the precise value of the SF has direct consequences on the critical properties and mechanisms of systems undergoing a phase transition. By analyzing the melting of n-alkanes (hexane C6, dodecane C12, tetracosane C24) on graphite, we show that the SF is not a universal feature, that it monotonically decreases with the molecular length, and that it drives a cross-over between two distinct mechanisms for melting in such systems.