Ab initio Calculations of Structure and Elastic Properties of Lightweight High-Entropy Alloys (HEAs).*

High Entropy Alloys (HEAs) are a new class of metallic alloys with 5 or more principal elements, with the concentration of 5% to 35% each one. Despite the complex composition, HEAs are believed to form simple crystal structures, depending on the valence electron concentration VEC (BCC if VEC<6.8, FCC if VEC>8, mixed phases in between). Due to their unusual design, these alloys often exhibit special properties. The combination of such properties as low density, high strength, and corrosion resistance makes possible many potential applications of HEAs in aviation, engineering, orthopedics (bone implants), etc. The aim of our work is to study the atomic structure as well as the electronic and elastic properties of lightweight HEAs using density functional theory and evolutionary crystallography methods. The methodology is tested by calculating and comparing the elastic properties with the existing data for certain alloys.