Discovering novel VC1−x compounds through hybrid first-principles and evolutionary algorithms

• Evolutionary algorithm USPEX was performed to find potentially stable vanadium carbides.
• The Pnnm-V2C is a newly discovered structure with lower energy than previously reported Pbcn-V2C.
• Vanadium rearrangement results in the strengthening of mechanical strength.

VC1−x compounds, known as ultra-high temperature ceramics, are able to maintain stability in a range of chemical compositions. Herein, using evolutionary algorithm USPEX, we performed a global search for potentially stable VC1−x compounds. We have discovered two stable compounds (P3112-V6C5 and Pnnm-V2C) and a number of near-ground-state compounds (Fm3¯m-VC, P4332-V8C7, P1¯-V5C4, I4¯3m-V4C3, Cmcm-V3C2, and Cmcm-V3C). The stable Pnnm-V2C is a new structure with lower total energy than experimentally reported α-V2C. Based on these stable and meta-stable VC1−x compounds, we have systemically investigated their structures, mechanical properties, and chemical bonding. We found that Cmcm-V3C2 and Cmcm-V3C display different arrangements of vanadium from other VC1−x compounds. We suggest that such rearrangement of vanadium are able to enhance mechanical strength. Most of VC1−x compounds possess very good mechanical properties, indicating that they have potential to be utilized for structural applications.