9 research outputs found
Implementation and benchmark of a long-range corrected functional in the density functional based tight-binding method
Bridging the gap between first principles methods and empirical schemes, the
density functional based tight-binding method (DFTB) has become a versatile
tool in predictive atomistic simulations over the past years. One of the major
restrictions of this method is the limitation to local or gradient corrected
exchange-correlation functionals. This excludes the important class of hybrid
or long-range corrected functionals, which are advantageous in thermochemistry,
as well as in the computation of vibrational, photoelectron and optical
spectra. The present work provides a detailed account of the implementation of
DFTB for a long-range corrected functional in generalized Kohn-Sham theory. We
apply the method to a set of organic molecules and compare ionization
potentials and electron affinities with the original DFTB method and higher
level theory. The new scheme cures the significant overpolarization in electric
fields found for local DFTB, which parallels the functional dependence in first
principles density functional theory (DFT). At the same time the computational
savings with respect to full DFT calculations are not compromised as evidenced
by numerical benchmark data
Towards a simplified description of thermoelectric materials: Accuracy of approximate density functional theory for phonon dispersions
We calculate the phonon-dispersion relations of several two-dimensional
materials and diamond using the density-functional based tight-binding approach
(DFTB). Our goal is to verify if this numerically efficient method provides
sufficiently accurate phonon frequencies and group velocities to compute
reliable thermoelectric properties. To this end, the results are compared to
available DFT results and experimental data. To quantify the accuracy for a
given band, a descriptor is introduced that summarizes contributions to the
lattice conductivity that are available already in the harmonic approximation.
We find that the DFTB predictions depend strongly on the employed repulsive
pair-potentials, which are an important prerequisite of this method. For
carbon-based materials, accurate pair-potentials are identified and lead to
errors of the descriptor that are of the same order as differences between
different local and semi-local DFT approaches
Atomic level modeling of extremely thin silicon-on-insulator MOSFETs including the silicon dioxide: Electronic structure
© 1963-2012 IEEE. Ultimate scaling of Si MOSFETs leads to extremely thin and short channels, which are justifiably modeled at the atomic level. Currently, hydrogen passivation of the channel is used in device models, as a compromise between efficiency and accuracy. This paper advances the state of the art by adopting a density-functional tight-binding Hamiltonian, permitting the inclusion of the confining amorphous oxide explicitly in the simulation domain in a way similar to ab initio approaches. Band structure of silicon-on-insulator films of different thicknesses is studied with this method, showing good agreement with the experiment and revealing large quantitative differences in comparison with simulations of H-passivated Si film.published_or_final_versio
The state of Fortran
A community of developers has formed to modernize the Fortran ecosystem. In this article, we describe the high-level features of Fortran that continue to make it a good choice for scientists and engineers in the 21st century. Ongoing efforts include the development of a Fortran standard library and package manager, the fostering of a friendly and welcoming online community, improved compiler support, and language feature development. The lessons learned are common across contemporary programming languages and help reduce the learning curve and increase adoption of Fortran
Accurate defect levels obtained from the HSE06 range-separated hybrid functional
Defect levels are a problem for standard implementations of density-functional theory and the error also influences the energetics. We demonstrate that the HSE06 functional, which describes the electronic structure of all group-IV semiconductors well (including Ge), gives highly accurate charge transition levels, too, if the defect wave function is host related-independent of localization. The degree of fulfilling the generalized Koopmans theorem shows the reliability of the results and the highest-occupied eigenvalue always seems to give the correct vertical ionization energy.Original Publication:Peter Deak, Balint Aradi, Thomas Frauenheim, Erik Janzén and Adam Gali, Accurate defect levels obtained from the HSE06 range-separated hybrid functional, 2010, PHYSICAL REVIEW B, (81), 15, 153203.http://dx.doi.org/10.1103/PhysRevB.81.153203Copyright: American Physical Societyhttp://www.aps.org
Accurate defect levels obtained from the HSE06 range-separated hybrid functional
Defect levels are a problem for standard implementations of density-functional theory and the error also influences the energetics. We demonstrate that the HSE06 functional, which describes the electronic structure of all group-IV semiconductors well (including Ge), gives highly accurate charge transition levels, too, if the defect wave function is host related-independent of localization. The degree of fulfilling the generalized Koopmans theorem shows the reliability of the results and the highest-occupied eigenvalue always seems to give the correct vertical ionization energy.Original Publication:Peter Deak, Balint Aradi, Thomas Frauenheim, Erik Janzén and Adam Gali, Accurate defect levels obtained from the HSE06 range-separated hybrid functional, 2010, PHYSICAL REVIEW B, (81), 15, 153203.http://dx.doi.org/10.1103/PhysRevB.81.153203Copyright: American Physical Societyhttp://www.aps.org
Using DFTB to Model Photocatalytic Anatase-Rutile TiO2 Nanocrystalline Interfaces and Their Band Alignment
Band alignment effects of anatase and rutile nanocrystals in TiO2 powders lead to electron-hole separation, increasing the photocatalytic efficiency of these powders. While size effects and types of possible alignments have been extensively studied, the effect of interface geometries of bonded nanocrystal structures on the alignment is poorly understood. To allow conclusive studies of a vast variety of bonded systems in different orientations, we have developed a new density functional tight-binding parameter set to properly describe quantum confinement in nanocrystals. By applying this set, we found a quantitative influence of the interface structure on the band alignment.Title in WoS: Using DFTB to Model Photocatalytic Anatase-Rutile TiO2 Nanocrystalline Interfaces and Their Band Alignment</p
DFT Exchange: Sharing Perspectives on the Workhorse of Quantum Chemistry and Materials Science
In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method developers and practitioners. The format of the paper is that of a roundtable discussion, in which the participants express and exchange views on DFT in the form of 300 individual contributions, formulated as responses to a preset list of 26 questions. Supported by a bibliography of 776 entries, the paper represents a broad snapshot of DFT, anno 2022