A Modified Elastic Constant Calculation Method for Triclinic-Like Special Quasi-Random Structures: Application to Pd-M (M = Cu, Ag) Solid Solutions

The mechanical properties of Palladium alloys need to be calculated using first principles due to high experiment cost. For FCC disordered Pd alloys, special quasi-random structure (SQS) is usually used for modeling at first and the calculation of mechanical properties usually begins with elastic constants. However, SQS supercells are often triclinic-like and show lower symmetry than origin FCC structure, which would lead to the elements of elastic matrix calculated by DFT aren't equal to elastic constants. To solve this problem, a strain operation method is put forward by linear transformation, L-SQS' = SDL, to modify energy-strain method. Taking Pd-M (M = Cu, Ag) random alloys as an application case, the elastic properties of Pd-Cu and Pd-Ag alloys with 5 at% concentration gradient are calculated. The calculation results are similar to experiment data and other DFT works, which indicate that the preceding formula is valid. Electron structure analysis shows that Pd valence electrons are the main contributors to metallic bonds.