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Abstract EPW is an open-source software for ab initio 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, and to perform predictive calculations of temperature-dependent properties and phonon-assisted quantum processes in bulk solids and low-dimensional materials. Here, we report on significant developments in the code since 2016, namely: a transport module for the calculation of charge carrier mobility under electric and magnetic fields using the Boltzmann transport equation; a superconductivity module for calculations of phonon-mediated superconductors using 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; and a module for calculating 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. 

Reported Li–B–C compounds and calculated phase diagram establishing conditions required for LiBC delithiation.

 

A new member of the transition metal dichalcogenide (TMD) family, 2M-WS 2, has been recently discovered and shown to display superconductivity with a critical temperature (Tc) of 8.8 K, the highest Tc among superconducting TMDs at ambient pressure. Using first-principles calculations combined with the Migdal-Eliashberg formalism, we explore how the superconducting properties of 2M-WS 2 can be enhanced through doping. Mo, Nb, and Ta are used as dopants at the W sites, while Se is used at the S sites. We demonstrate that the monotonous decrease in the Tc observed experimentally for Mo and Se doping is due to the decrease in density of states at the Fermi level and the electron–phonon coupling of the low-energy phonons. In addition, we find that a noticeable increase in the electron–phonon coupling could be achieved when doping with Nb and Ta, leading to an enhancement of the Tc of up to 50% compared to the undoped compound. 

The tin-selenide and tin-sulfide classes of materials undergo multiple structural transitions under high pressure leading to periodic lattice distortions, superconductivity, and topologically non-trivial phases, yet a number of controversies exist regarding the structural transformations in these systems. We perform first-principles calculations within the framework of density functional theory and a careful comparison of our results with available experiments on SnSe 2 reveals that the apparent contradictions among high-pressure results can be attributed to differences in experimental conditions. We further demonstrate that under hydrostatic pressure a superstructure can be stabilized above 20 GPa in SnS 2 via a periodic lattice distortion as found recently in the case of SnSe 2 , and that this pressure-induced phase transition is due to the combined effect of Fermi surface nesting and electron–phonon coupling at a momentum wave vector q = (1/3, 1/3, 0). In addition, we investigate the contribution of nonadiabatic corrections on the calculated phonon frequencies, and show that the quantitative agreement between theory and experiment for the high-energy A 1g phonon mode is improved when these effects are taken into account. Finally, we examine the nature of the superconducting state recently observed in SnSe 2 under nonhydrostatic pressure and predict the emergence of superconductivity with a comparable critical temperature in SnS 2 under similar experimental conditions. Interestingly, in the periodic lattice distorted phases, the critical temperature is found to be reduced by an order of magnitude due to the restructuring of the Fermi surface.