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Register a new userWloopPHI: A tool for ab initio characterization of Weyl semimetals
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WloopPHI is a Python code that expands the features of WIEN2k, a full-potential all-electron density functional theory package, by the characterization of Weyl semimetals. It enables the calculation of the chirality (or monopole charge) associated with Weyl nodes and nodal lines. The theoretical methodology for the calculation of the chirality is based on an extended Wilson loop method and a Berry phase approach. We validate the code using TaAs, which is a well-characterized Weyl semimetal, both theoretically and experimentally. Afterwards, we applied the method to the characterization of YRh$_6$Ge$_4$ and found two sets of Weyl points (ca. 0.2 eV below the Fermi energy) together with a topological nodal line (protected by mirror symmetry) crossing the Fermi energy and mapped their chiralities.
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We study the general problem of mixing for ab-initio quantum-mechanical problems. Guided by general mathematical principles and the underlying physics, we propose a multisecant form of Broydens second method for solving the self-consistent field equations of Kohn-Sham density functional theory. The algorithm is robust, requires relatively little finetuning and appears to outperform the current state of the art, converging for cases that defeat many other methods. We compare our technique to the conventional methods for problems ranging from simple to nearly pathological.
First-principles calculation predict that olivine Li4MnFeCoNiP4O16 has ferrotoroidic characteristic and ferrimagnetic configuration with magnetic moment of 1.56 muB per formula unit. The ferrotoroidicity of this material makes it a potential candidate for magnetoelectric materials . Based on the orbital-resolved density of states for the transtion-metal ions in Li4MnFeCoNiP4O16, the spin configuration for Mn2+,Fe3+,Co2+, and Ni2+ is t2g3eg2, t2g3eg2,t2g1t2g3eg1eg2, and t2g2t2g3eg1eg2, respectively. Density functional theory plus U (DFT+U) shows a indirect band gap of 1.25 eV in this predicted material, which is not simply related to the electronic conductivity in terms of being used as cathode material in rechargeable Li-ion batteries.
RESPACK is a first-principles calculation software for evaluating the interaction parameters of materials and is able to calculate maximally localized Wannier functions, response functions based on the random phase approximation and related optical properties, and frequency-dependent electronic interaction parameters. RESPACK receives its input data from a band-calculation code using norm-conserving pseudopotentials with plane-wave basis sets. Automatic generation scripts that convert the band-structure results to the RESPACK inputs are prepared for xTAPP and Quantum ESPRESSO. An input file for specifying the RESPACK calculation conditions is designed pursuing simplicity and is given in the Fortran namelist format. RESPACK supports hybrid parallelization using OpenMP and MPI and can treat large systems including a few hundred atoms in the calculation cell.
So far, the circular photogalvanic effect (CPGE) is the only possible quantized signal in Weyl semimetals. With inversion and mirror symmetries broken, Weyl and multifold fermions in band structures with opposite chiralities can stay at different energies and generate a net topological charge. Such kind of net topological charge can present as a quantized signal in the circular polarized light induced injection current. According to current theoretical understanding, RhSi and its counterparts are believed to be the most promising candidate for the experimental observation of the quantized CPGE. However, the real quantized signal was not experimentally observed to date. Since all the previous theoretical studies for the quantized CPGE were based on effective model but not realistic band structures, it should lose some crucial details that influence the quantized signal. The current status motives us to perform a realistic ab-initio study for the CPGE. Our result shows that the quantized value is very easy to be interfered by trivial bands related optic transitions, and an fine tuning of the chemical potential by doping is essential for the observation of quantized CPGE. This work performs the first ab-initio analysis for the quantized CPGE based on realistic electronic band structure and provides an effective way to solve the current problem for given materials.
The anomalous plasmon linewidth dispersion (PLD) measured in K by vom Felde, Sprosser-Prou, and Fink (Phys. Rev. B 40, 10181 (1989)), has been attributed to strong dynamical electron-electron correlations. On the basis of ab initio response calculations, and detailed comparison with experiment, we show that the PLD of K is, in fact, dominated by decay into particle-hole excitations involving empty states of d-symmetry. For Li, we shed new light on the physics of the PLD. Our all-electron results illustrate the importance of ab initio methods for the study of electronic excitations.
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