With AFLOWπ we introduce a minimalist framework for high-throughput first principles calculations that it easy to install and operate. The key components involve robust data generation, real time feedback and error control, curation and archival of the data, and post-processing tools for analysis and visualization. AFLOWπ simplifies the process of managing large sets of calculations to determine band strucures, density of states, phonon dispersions, elastic properties, complex dielectric constants, diffusive transport coefficients.
The software is implemented in Python2.7 (using the Python standard library and NumPy, Scipy, and matplotlib). The systematic use of regular expression (re module) to parse and modify the input and output files according the specific workflow makes the software very portable and expandable to a variety of electronic structure engines and tools. Currently, AFLOWπ encapsulates pw.x and several post-processing software from the Quantum Espresso package as well as ElaStic. In addition it uses features of findsym. The generation and manipulation of the TB Hamiltonians is done with the engine PAOπ.
Theory and applications of the methodology used by AFLOWπ to generate tight-binding (TB) hamiltonians for first principles plane-wave pseudopotential calculations have been discussed in Refs. [Agapito 2013, 2016a, 2016b]. Our implementation does not require any additional input with respect to the electronic structure calculations and pro- vides the real space representation of the TB matrix in self-contained XML format. The sparse TB matrix is represented on a real space grid that can be easily Fourier transformed and diagonalized to determine the full energy dispersion with the desired level of resolution in reciprocal space or to compute additional properties associated with derivatives in reciprocal space (linear momenta, and effective masses). The real space repre- sentation can also be used directly. We have recently applied these methodologies to study diffusive and bal- listic transport as well as the optical properties in the independent particles approximation [D'Amico 2016].
The TB representation of the electronic structure can be exploited to efficiently compute two-electron integrals for the development of local exchange functionals. AFLOWπ implements the direct and self-consistent evaluation of the on-site Hubbard U correction that greatly improves the accuracy of standard DFT calculations [Agapito 2015]. Due to the accurate TB representation, the evaluation of the U parameters for atoms in dif- ferent chemical environments or close to topological defects becomes trivial and AFLOWπ facilitates the investigation of such systems. ACBN0 only demands computational resources comparable to regular LDA or PBE calculations. We have extensively investigated the improvements and the limits of ACBN0 calculation in Refs. [Gopal 2015, Shishkin 2016]. Overall, ACBN0 delivers better accuracy for lattice parameters and bulk moduli, improves the energy band gap on semiconductors and insulators as well as the relative position of occupied d-manifolds in transition metal oxides, and optimizes the phonon dispersions and associated thermal transport properties.