An ab initio study on the transition paths from graphite to diamond under pressure

Area of Science:

• Materials Science
• Computational Chemistry
• Solid-State Physics

Background:

• Graphite and diamond are allotropes of carbon with distinct structures and properties.
• Understanding phase transitions between carbon allotropes is crucial for materials science.
• Previous studies have explored graphite-to-diamond transformations, but pathways and energy barriers require further investigation.

Purpose of the Study:

• To calculate and compare transition paths for graphite transforming into cubic and hexagonal diamond.
• To analyze the electronic structure changes, specifically π to σ bond transitions, during the graphite to cubic diamond phase change.
• To discover and characterize novel transition pathways and intermediate states for graphite to hexagonal diamond transformation.

Main Methods:

• Variable cell nudged elastic band (VCN EB) method was employed for calculating transition paths.
• Detailed analysis of electronic structure, focusing on π and σ bonding, was performed.
• Computational simulations were used to identify and characterize intermediate bonding configurations.

Main Results:

• The study details the π to σ bond transition during graphite to cubic diamond transformation.
• A novel transition path with a reduced energy barrier was identified for graphite to hexagonal diamond conversion.
• This new path features unique sp(2)-sp(3) bonding configurations at the transition state.

Conclusions:

• The discovered sp(2)-sp(3) transition state offers a more energetically favorable route for graphite to hexagonal diamond conversion.
• These findings suggest that sp(2)-sp(3) bonding configurations may represent a general phenomenon in cold-compressed graphite.
• The research provides valuable insights into the fundamental mechanisms of carbon allotrope phase transitions.