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

Abstract VC 1− 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 VC 1− x compounds. We have discovered two stable compounds ( P 3 1 12-V 6 C 5 and Pnnm -V 2 C) and a number of near-ground-state compounds ( Fm 3 ¯ m -VC, P 4 3 32-V 8 C 7 , P 1 ¯ -V 5 C 4 , I 4 ¯ 3 m -V 4 C 3 , Cmcm -V 3 C 2 , and Cmcm -V 3 C). The stable Pnnm -V 2 C is a new structure with lower total energy than experimentally reported α -V 2 C. Based on these stable and meta-stable VC 1− x compounds, we have systemically investigated their structures, mechanical properties, and chemical bonding. We found that Cmcm -V 3 C 2 and Cmcm -V 3 C display different arrangements of vanadium from other VC 1− x compounds. We suggest that such rearrangement of vanadium are able to enhance mechanical strength. Most of VC 1− x compounds possess very good mechanical properties, indicating that they have potential to be utilized for structural applications.