38 research outputs found
Ab Initio Electron-Phonon Interactions Using Atomic Orbital Wavefunctions
The interaction between electrons and lattice vibrations determines key
physical properties of materials, including their electrical and heat
transport, excited electron dynamics, phase transitions, and superconductivity.
We present a new ab initio method that employs atomic orbital (AO)
wavefunctions to compute the electron-phonon (e-ph) interactions in materials
and interpolate the e-ph coupling matrix elements to fine Brillouin zone grids.
We detail the numerical implementation of such AO-based e-ph calculations, and
benchmark them against direct density functional theory calculations and
Wannier function (WF) interpolation. The key advantages of AOs over WFs for
e-ph calculations are outlined. Since AOs are fixed basis functions associated
with the atoms, they circumvent the need to generate a material-specific
localized basis set with a trial-and-error approach, as is needed in WFs.
Therefore, AOs are ideal to compute e-ph interactions in chemically and
structurally complex materials for which WFs are challenging to generate, and
are also promising for high-throughput materials discovery. While our results
focus on AOs, the formalism we present generalizes e-ph calculations to
arbitrary localized basis sets, with WFs recovered as a special case
Charge Transport in Organic Molecular Semiconductors from First Principles: The Band-Like Hole Mobility in Naphthalene Crystal
Predicting charge transport in organic molecular crystals is notoriously
challenging. Carrier mobility calculations in organic semiconductors are
dominated by quantum chemistry methods based on charge hopping, which are
laborious and only moderately accurate. We compute from first principles the
electron-phonon scattering and the phonon-limited hole mobility of naphthalene
crystal in the framework of ab initio band theory. Our calculations combine GW
electronic bandstructures, ab initio electron-phonon scattering, and the
Boltzmann transport equation. The calculated hole mobility is in very good
agreement with experiment between 100300 K, and we can predict its
temperature dependence with high accuracy. We show that scattering between
inter-molecular phonons and holes regulates the mobility, though
intra-molecular phonons possess the strongest coupling with holes. We revisit
the common belief that only rigid molecular motions affect carrier dynamics in
organic molecular crystals. Our work provides a quantitative and rigorous
framework to compute charge transport in organic crystals, and is a first step
toward reconciling band theory and carrier hopping computational methods.Comment: 7 pages, 4 figures, Accepted by Phys. Rev.
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Electric-Field Control of Magnetism in Graphene Quantum Dots: Ab Initio Calculations
Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state can be accomplished by exploiting the distinctive electrical properties of the various magnetic configurations.Engineering and Applied SciencesPhysic
Novel Family of Chiral-Based Topological Insulators: Elemental Tellurium under Strain
Employing ab initio electronic structure calculations, we predict that trigonal tellurium consisting of weakly interacting helical chains undergoes a trivial insulator to strong topological insulator (metal) transition under shear (hydrostatic or uniaxial) strain. The transition is demonstrated by examining the strain evolution of the band structure, the topological Z_2 invariant and the concomitant band inversion. The underlying mechanism is the depopulation of the lone-pair orbitals associated with the valence band via proper strain engineering. Thus, Te becomes the prototype of a novel family of chiral-based three-dimensional topological insulators with important implications in spintronics, magneto-optics, and thermoelectrics
Approaching the Intrinsic Bandgap in Suspended High-Mobility Graphene Nanoribbons
We report electrical transport measurements on a suspended ultra-low-disorder
graphene nanoribbon(GNR) with nearly atomically smooth edges that reveal a high
mobility exceeding 3000 cm2 V-1 s-1 and an intrinsic band gap. The
experimentally derived bandgap is in quantitative agreement with the results of
our electronic-structure calculations on chiral GNRs with comparable width
taking into account the electron-electron interactions, indicating that the
origin of the bandgap in non-armchair GNRs is partially due to the magnetic
zigzag edges.Comment: 22 pages, 6 figure