High-Throughput

To perform the very large number of calculations, we have to implement a set of automatic tools to prepare intitial data, perform calculations, and analyze the results

Preparation of input files: All input files should be prepared by starting from templates based on prototype chemistry. The initial volume of a unit cell is determined as a linear combination of the atomic volumes of the pure elements [1]. Internal positions of atoms are either generated automatically (for fcc, bcc, hcp superstructures) or are extracted from the CRYSTMET and Pauling File databases.

Ab-initio Calculations: Calculations are performed using a high-throughput tool called AFLOW (automatic flow), which automatically searches for unfinished calculations, initiates a calculation, and monitors its progress through to completion.

 Details of the high-throughput error checking process can be found in Stefano Curtarolo's Thesis.

Ground State Energy

The ground state energy is the zero temperature (and pressure) energy of a compound (e.g. Ag₃Cd) in a particular crystal structure. This quantity is calculated using ab initio techniques based on DFT (VASP, Wien2K, FHI..) which solves the Kohn-Sham equations for the electronic degrees of freedom and evolves structural parameters to their local energy minimum (provided it exists). The ground state energy does not include entropic effects due to available excitations such as atomic vibrations, site exchanges, and electronic excitations. In addition, zero-point fluctuation corrections are also ignored. While the ground state energy is a good indication of the stability of a compound at zero temperature, it is possible that stability changes with temperature due to differences in entropy between the stable and unstable structures. This is particularly true for structures whose ground state energy is within k_BT of the stable structure.

Exemples