Turnover of the melting line of highly compressed molecular hydrogen

TL;DR

This study uses molecular dynamics to explore how the melting temperature of highly compressed hydrogen varies with pressure, revealing a smooth increase that turns negative at megabar pressures, linked to changes in chemical bonding.

Contribution

It provides new insights into the melting behavior of compressed hydrogen and connects the melting line turnover to chemical bonding parameters.

Findings

Melting temperature increases smoothly with pressure

At megabar pressures, the melting slope becomes negative

Turnover linked to changes in H2 chemical bonding

Abstract

Conventional molecular dynamics simulation has been used to determine melting temperature of highly compressed classical molecular hydrogen in a wide range of pressures and temperatures using non-empirical atom-atom potentials approximation. It is shown that the raise of melting temperature with increasing pressure becomes more and more smooth and at megabar pressures its slope goes negative. We discuss the reasons of this turnover and analyze connection of this effect with the parameters of chemical bonding in H2.