Automated quantum conductance calculations using maximally-localised Wannier functions

Shelley, Matthew; Poilvert, Nicolas; Mostofi, Arash A.; Marzari, Nicola

doi:10.1016/j.cpc.2011.05.017

Cited by 33 publications

(42 citation statements)

References 41 publications

(49 reference statements)

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“…Our method (described in detail elsewhere [12]), in which accurate yet compact model Hamiltonians of largescale systems are constructed from first-principles calculations, enables us to study transport through meso-scale systems with modest computational cost: our largest simulations consist of a conductor region of length 116 nm (8432 atoms) coupled to semi-infinite leads. Our procedure is largely automated, which has made it possible to perform high-throughput calculations and undertake a comprehensive study of a large structural parameter space.…”

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confidence: 99%

Prediction of high zT in thermoelectric silicon nanowires with axial germanium heterostructures

Shelley

Mostofi

2011

EPL

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-We calculate the thermoelectric figure of merit, zT = S 2 GT /(κ l + κe), for p-type Si nanowires with axial Ge heterostructures using a combination of first-principles density-functional theory, interatomic potentials, and Landauer-Buttiker transport theory. We consider nanowires with up to 8400 atoms and twelve Ge axial heterostructures along their length. We find that introducing heterostructures always reduces S 2 G, and that our calculated increases in zT are predominantly driven by associated decreases in κ l . Of the systems considered, ⟨111⟩ nanowires with a regular distribution of Ge heterostructures have the highest figure-of-merit: zT = 3, an order of magnitude larger than the equivalent pristine nanowire. Even in the presence of realistic structural disorder, in the form of small variations in length of the heterostructures, zT remains several times larger than that of the pristine case, suggesting that axial heterostructuring is a promising route to high-zT thermoelectric nanowires.

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confidence: 99%

Prediction of high zT in thermoelectric silicon nanowires with axial germanium heterostructures

Shelley

Mostofi

2011

EPL

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“…This approach combines plane-wave calculations with the use of a minimal basis set suitable for quantum transport calculations. 36,37,43,49,50 When one is dealing with lowdimensional systems and subtle band-structure effects such as spin-orbit coupling, the accuracy of electronic-structure description becomes crucial. Therefore, the application of a highly precise all-electron full-potential linearized augmented plane-wave code is desirable.…”

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confidence: 99%

One-dimensional ballistic transport with FLAPW Wannier functions

et al. 2012

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We present an implementation of the ballistic Landauer-Büttiker transport scheme in one-dimensional systems based on density functional theory calculations within the full-potential linearized augmented plane-wave (FLAPW) method. In order to calculate the conductance within the Green's function method, we map the electronic structure from the extended states of the FLAPW calculation to Wannier functions, which constitute a minimal localized basis set. Our approach benefits from the high accuracy of the underlying FLAPW calculations, allowing us to address the complex interplay of structure, magnetism, and spin-orbit coupling and is ideally suited to study spin-dependent electronic transport in one-dimensional magnetic nanostructures. To illustrate our approach, we study ballistic electron transport in nonmagnetic Pt monowires with a single stretched bond including spin-orbit coupling, and in ferromagnetic Co monowires with different collinear magnetic alignment of the electrodes with the purpose of analyzing the magnetoresistance when going from tunneling to the contact regime. We further investigate spin-orbit scattering due to an impurity atom. We consider two configurations: a Co atom in a Pt monowire and vice versa. In both cases, the spin-orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it. The main contribution stems from ballistic spin scattering for the magnetic Co impurity in the nonmagnetic Pt monowire, and for the Pt scatterer in the magnetic Co monowire from the band formed from states with d xy and d x 2 −y 2 orbital symmetry. We quantify this effect by calculating the ballistic anisotropic magnetoresistance, which displays values up to as much as 7% for ballistic spin scattering and gigantic values of around 100% for the Pt impurity in the Co wire. In addition, we show that the presence of a scatterer can reduce as well as increase the ballistic anisotropic magnetoresistance.

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“…TiMeS currently has interfaces to accept this information from OpenMX, [35][36][37] DFTB þ , 27 and the Quantum Espresso plane-wave DFT code via transformation to Wannier orbitals. 41,42 Like other localized-orbital electronic transport codes based on Landauer or NEGF theory, [21][22][23][24] TiMeS calculates the self-energy of the semi-infinite electrodes based on the surface Green's function for the given "on-site" and "hopping" Hamiltonian and overlap matrices for the electrodes. 43 The entire transport region is broken into three sub-regions: the two electrodes and a scattering region (see Fig.…”

Section: B Transport Propertiesmentioning

confidence: 99%

Transport properties and electrical device characteristics with the TiMeS computational platform: Application in silicon nanowires

Sharma

Ansari

Feldman

et al. 2013

Journal of Applied Physics

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Nanoelectronics requires the development of a priori technology evaluation for materials and device design that takes into account quantum physical effects and the explicit chemical nature at the atomic scale. Here, we present a cross-platform quantum transport computation tool. Using first-principles electronic structure, it allows for flexible and efficient calculations of materials transport properties and realistic device simulations to extract current-voltage and transfer characteristics. We apply this computational method to the calculation of the mean free path in silicon nanowires with dopant and surface oxygen impurities. The dependence of transport on basis set is established, with the optimized double zeta polarized basis giving a reasonable compromise between converged results and efficiency. The current-voltage characteristics of ultrascaled (3 nm length) nanowire-based transistors with p-i-p and p-n-p doping profiles are also investigated. It is found that charge self-consistency affects the device characteristics more significantly than the choice of the basis set. These devices yield sourced-drain tunneling currents in the range of 0.5 nA (p-n-p junction) to 2 nA (p-i-p junction), implying that junctioned transistor designs at these length scales would likely fail to keep carriers out of the channel in the off-state. (C) 2013 AIP Publishing LLC

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Automated quantum conductance calculations using maximally-localised Wannier functions

Cited by 33 publications

References 41 publications

Prediction of high zT in thermoelectric silicon nanowires with axial germanium heterostructures

Prediction of high zT in thermoelectric silicon nanowires with axial germanium heterostructures

One-dimensional ballistic transport with FLAPW Wannier functions

Transport properties and electrical device characteristics with the TiMeS computational platform: Application in silicon nanowires

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