Superhard F-carbon predicted by ab initio particle-swarm optimization methodology

Area of Science:

• Materials Science
• Computational Chemistry
• Solid State Physics

Background:

• Graphite, a common carbon allotrope, can transform into various metastable phases under extreme conditions.
• Understanding these high-pressure carbon phases is crucial for developing new materials with unique properties.

Purpose of the Study:

• To propose and characterize a new sp(3) carbon allotrope, termed F-carbon.
• To investigate the stability, electronic, and mechanical properties of F-carbon.
• To explore the potential formation of F-carbon from cold-compressed graphite.

Main Methods:

• Ab initio particle-swarm optimization for crystal structure prediction.
• Band structure and hardness calculations.
• Variable cell nudged elastic band method for transition pathway analysis.

Main Results:

• F-carbon, an eight-atom unit cell (5+6+7)-sp(3) carbon, was computationally discovered.
• F-carbon is energetically more stable than 2H-graphite above 13.9 GPa.
• Calculations predict F-carbon to be a transparent superhard material with a 4.55 eV band gap at 15 GPa and 93.9 GPa hardness at zero pressure.
• Simulated X-ray diffraction patterns of F-carbon match experimental data for cold-compressed graphite phases.
• Transition routes and energy barriers for graphite compression were simulated.

Conclusions:

• F-carbon represents a novel, stable, transparent, and superhard carbon allotrope.
• The findings suggest that F-carbon could be a metastable phase formed during the cold compression of graphite.
• The study highlights the potential for discovering new carbon materials with exceptional properties through advanced computational simulations.