6 research outputs found
Structurally Constrained Evolutionary Algorithm for the Discovery and Design of Metastable Phases
Metastable materials are abundant in nature and technology, showcasing
remarkable properties that inspire innovative materials design. However,
traditional crystal structure prediction methods, which rely solely on
energetic factors to determine a structure's fitness, are not suitable for
predicting the vast number of potentially synthesizable phases that represent a
local minimum corresponding to a state in thermodynamic equilibrium. Here, we
present a new approach for the prediction of metastable phases with specific
structural features, and interface this method with the XtalOpt evolutionary
algorithm. Our method relies on structural features that include the local
crystalline order (e.g., the coordination number or chemical environment), and
symmetry (e.g., Bravais lattice and space group) to filter the parent pool of
an evolutionary crystal structure search. The effectiveness of this approach is
benchmarked on three known metastable systems: XeN, with a two-dimensional
polymeric nitrogen sublattice, brookite TiO, and a high pressure BaH
phase that was recently characterized. Additionally, a newly predicted
metastable melaminate salt, -1 WCN, was found to possess an
energy that is lower than two phases proposed in a recent computational study.
The method presented here could help in identifying the structures of compounds
that have already been synthesized, and developing new synthesis targets with
desired properties
Electron-phonon physics from first principles using the EPW code
EPW is an open-source software for calculations of
electron-phonon interactions and related materials properties. The code
combines density functional perturbation theory and maximally-localized Wannier
functions to efficiently compute electron-phonon coupling matrix elements on
ultra-fine Brillouin zone grids. This data is employed for predictive
calculations of temperature-dependent properties and phonon-assisted quantum
processes in bulk solids and low-dimensional materials. Here, we report on
significant new developments in the code that occurred during the period
2016-2022, namely: a transport module for the calculation of charge carrier
mobility and conductivity under electric and magnetic fields within the
Boltzmann transport equation; a superconductivity module
for the calculation of critical temperature and gap structure in
phonon-mediated superconductors within the anisotropic
multi-band Eliashberg theory; an optics module for calculations of
phonon-assisted indirect transitions; a module for the calculation of small and
large polarons without supercells using the polaron
equations; and a module for calculating electron-phonon couplings, band
structure renormalization, and temperature-dependent optical spectra using the
special displacement method. For each capability, we outline the methodology
and implementation, and provide example calculations. We describe recent code
refactoring to prepare EPW for exascale architectures, we discuss efficient
parallelization strategies, and report on extreme parallel scaling tests.Comment: 61 pages, 9 figure
Structurally Constrained Evolutionary Algorithm for the Discovery and Design of Metastable Phases
Metastable materials are abundant in nature and technology, showcasing remarkable properties that inspire innovative materials design. However, traditional crystal structure prediction methods, which rely solely on energetic factors to determine a structure's fitness, are not suitable for predicting the vast number of potentially synthesizable phases that represent a local minimum corresponding to a state in thermodynamic equilibrium. Here, we present a new approach for the prediction of metastable phases with specific structural features, and interface this method with the XTALOPT evolutionary algorithm. Our method relies on structural features that include the local crystalline order (e.g., the coordination number or chemical environment), and symmetry (e.g., Bravais lattice and space group) to filter the parent pool of an evolutionary crystal structure search. The effectiveness of this approach is benchmarked on three known metastable systems: XeN8 , with a two-dimensional polymeric nitrogen sublattice, brookite TiO2 , and a high pressure BaH 4 phase that was recently characterized. Additionally, a newly predicted metastable melaminate salt, P-1 WC3N6 , was found to possess an energy that is lower than two phases proposed in a recent computational study. The method presented here could help in identifying the structures of compounds that have already been synthesized, and developing new synthesis targets with desired properties
Full-bandwidth anisotropic Migdal-Eliashberg theory and its application to superhydrides
<p>QE input files for "Full-bandwidth anisotropic Migdal-Eliashberg theory and its application to superhydrides" by Roman Lucrezi, Pedro P. Ferreira, Samad Hajinazar, Hitoshi Mori, Hari Paudyal, Elena R. Margine, and Christoph Heil.</p>