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Register a new userDescribing Migdal effects in diamond crystal with atom-centered localized Wannier functions
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Recent studies have theoretically investigated the atomic excitation and ionization induced by the dark matter (DM)-nucleus scattering, and it is found that the suddenly recoiled atom is much more likely to excite or lose its electrons than expected. Such phenomenon is called the Migdal effect. In this paper, we extend the established strategy to describe the Migdal effect in isolated atoms to the case in semiconductors under the framework of tight-binding (TB) approximation. Since the localized aspects of electrons are respected in form of the Wannier functions (WFs), the extension of the existing Migdal approach for isolated atoms is much more natural, while the extensive nature of electrons in solids is reflected in the hopping integrals. We take diamond target as a concrete proof of principle for the methodology, and calculate relevant energy spectra and projected sensitivity of such diamond detector. It turns out that our method as a preliminary attempt is practically effective.
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We investigate a recently developed approach [P. L. Silvestrelli, Phys. Rev. Lett. 100, 053002 (2008); J. Phys. Chem. A 113, 5224 (2009)] that uses maximally localized Wannier functions to evaluate the van der Waals contribution to the total energy of a system calculated with density-functional theory. We test it on a set of atomic and molecular dimers of increasing complexity (argon, methane, ethene, benzene, phthalocyanine, and copper phthalocyanine) and demonstrate that the method, as originally proposed, has a number of shortcomings that hamper its predictive power. In order to overcome these problems, we have developed and implemented a number of improvements to the method and show that these modifications give rise to calculated binding energies and equilibrium geometries that are in closer agreement to results of quantum-chemical coupled-cluster calculations.
We review the formalisms of the self-consistent GW approximation to many-body perturbation theory and of the generation of optimally-localized Wannier functions from groups of energy bands. We show that the quasiparticle Bloch wave functions from such GW calculations can be used within this Wannier framework. These Wannier functions can be used to interpolate the many-body band structure from the coarse mesh of Brillouin zone points on which it is known from the initial calculation to the usual symmetry lines, and we demonstrate that this procedure is accurate and efficient for the self-consistent GW band structure. The resemblance of these Wannier functions to the bond orbitals discussed in the chemical community led us to expect differences between density-functional and many-body functions that could be qualitatively interpreted. However, the differences proved to be minimal in the cases studied. Detailed results are presented for SrTiO_3 and solid argon.
Orbital magnetic susceptibility involves rich physics such as interband effects despite of its conceptual simplicity. In order to appreciate the rich physics related to the orbital magnetic susceptibility, it is essential to derive a formula to decompose the susceptibility into the contributions from each band. Here, we propose a scheme to perform this decomposition using the modified Wannier functions. The derived formula nicely decomposes the susceptibility into intraband and interband contributions, and from the other aspect, into itinerant and local contributions. The validity of the formula is tested in a couple of simple models. Interestingly, it is revealed that the quality of the decomposition depends on the degree of localization of the used Wannier functions. The formula here complements another formula using Bloch functions, or the formula derived in the semiclassical theory, which deepens our understanding of the orbital magnetic susceptibility and may serve as a foundation of a better computational method. The relationship to the Berry curvature in the present scheme is also clarified.
We report on the implementation of the Wannier Functions (WFs) formalism within the full-potential linearized augmented plane wave method (FLAPW), suitable for bulk, film and one-dimensional geometries. The details of the implementation, as well as results for the metallic SrVO3, ferroelectric BaTiO3 grown on SrTiO3, covalently bonded graphene and a one-dimensional Pt-chain are given. We discuss the effect of spin-orbit coupling on the Wannier Functions for the cases of SrVO3 and platinum. The dependency of the WFs on the choice of the localized trial orbitals as well as the difference between the maximally localized and first-guess WFs are discussed. Our results on SrVO3 and BaTiO3, e.g. the ferroelectric polarization of BaTiO3, are compared to results published elsewhere and found to be in excellent agreement.
A method to calculate the crystal field parameters {it ab initio} is proposed and applied to trivalent rare earth impurities in yttrium aluminate and to Tb$^{3+}$ ion in TbAlO$_3$. To determine crystal field parameters local Hamiltonian expressed in basis of Wannier functions is expanded in a series of spherical tensor operators. Wannier functions are obtained by transforming the Bloch functions calculated using the density functional theory based program. The results show that the crystal field is continuously decreasing as the number of $4f$ electrons increases and that the hybridization of $4f$ states with the states of oxygen ligands is important. Theory is confronted with experiment for Nd$^{3+}$ and Er$^{3+}$ ions in YAlO$_3$ and for Tb$^{3+}$ ion in TbAlO$_3$ and a fair agreement is found.
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