scholarly journals Quantum Phonon Transport in Nanomaterials: Combining Atomistic with Non-Equilibrium Green’s Function Techniques

Entropy ◽  
2019 ◽  
Vol 21 (8) ◽  
pp. 735 ◽  
Author(s):  
Leonardo Medrano Sandonas ◽  
Rafael Gutierrez ◽  
Alessandro Pecchia ◽  
Alexander Croy ◽  
Gianaurelio Cuniberti
Keyword(s):  
Quantum Transport ◽  
Density Functional ◽  
Tight Binding ◽  
Phonon Transport ◽  
Design Strategies ◽  
Computationally Efficient ◽  
Phonon Thermal Conductivity ◽  
Doping Effects ◽  
Two Dimensional Materials ◽  
Non Equilibrium Green’S Function

A crucial goal for increasing thermal energy harvesting will be to progress towards atomistic design strategies for smart nanodevices and nanomaterials. This requires the combination of computationally efficient atomistic methodologies with quantum transport based approaches. Here, we review our recent work on this problem, by presenting selected applications of the PHONON tool to the description of phonon transport in nanostructured materials. The PHONON tool is a module developed as part of the Density-Functional Tight-Binding (DFTB) software platform. We discuss the anisotropic phonon band structure of selected puckered two-dimensional materials, helical and horizontal doping effects in the phonon thermal conductivity of boron nitride-carbon heteronanotubes, phonon filtering in molecular junctions, and a novel computational methodology to investigate time-dependent phonon transport at the atomistic level. These examples illustrate the versatility of our implementation of phonon transport in combination with density functional-based methods to address specific nanoscale functionalities, thus potentially allowing for designing novel thermal devices.

Mirror symmetry origin of Dirac cone formation in rectangular two-dimensional materials

2020 ◽  
Vol 22 (12) ◽  
pp. 6619-6625 ◽  
Author(s):  
Xuming Qin ◽  
Yi Liu ◽  
Gui Yang ◽  
Dongqiu Zhao
Keyword(s):  
Band Structure ◽  
Mirror Symmetry ◽  
Density Functional ◽  
Tight Binding ◽  
Coupling Mechanism ◽  
Two Dimensional ◽  
Dirac Cone ◽  
Two Dimensional Materials ◽  
Tight Binding Method ◽  
Cone Formation

The origin of Dirac cone band structure of 6,6,12-graphyne is revealed by a “mirror symmetry parity coupling” mechanism proposed with tight-binding method combined with density functional calculations.

Ab initio calculations of quantum transport of Au–GaN–Au nanoscale junctions

RSC Advances ◽  
2014 ◽  
Vol 4 (94) ◽  
pp. 51838-51844 ◽  
Author(s):  
Tian Zhang ◽  
Yan Cheng ◽  
Xiang-Rong Chen
Keyword(s):  
Density Functional Theory ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Transport Properties ◽  
Quantum Transport ◽  
Electronic Transport ◽  
Density Functional ◽  
Function Method ◽  
Functional Theory ◽  
Non Equilibrium Green’S Function

We investigate the contact geometry and electronic transport properties of a GaN pair sandwiched between Au electrodes by performing density functional theory plus the non-equilibrium Green's function method.

scholarly journals High Accuracy Semi-Empirical Quantum Models Based on a Reduced Training Set

2021 ◽  
Author(s):  
Cong Huy Pham ◽  
Rebecca Lindsey ◽  
Laurence Fried ◽  
Nir Goldman
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Coupled Cluster ◽  
Computationally Efficient ◽  
Learning Potential ◽  
Training Set ◽  
Cluster Accuracy ◽  
High Level ◽  
Physical And Chemical ◽  
Many Body Interactions

There exists a great need for computationally efficient quantum simulation approaches that can achieve an accuracy similar to high-level theories while exhibiting a wide degree of transferability. In this regard, we have leveraged a machine-learned force field based on Chebyshev polynomials to determine Density Functional Tight Binding (DFTB) models for organic materials. The benefit of our approach is two-fold: (1) many-body interactions can be corrected for in a systematic and rapidly tunable process, and (2) high-level quantum accuracy for a broad range of compounds can be achieved with ∼0.3% of data required for one advanced deep learning potential (ANI- 1x). In addition, the total number of data points in our training set is less than one half of that used for a recent DFTB-neural network model (trained on a separate dataset). Validation tests of our DFTB model against energy and vibrational data for gas-phase molecules for additional quantum datasets shows strong agreement with reference data from either hybrid density-functional theory, coupled-cluster calculations, or experiments. Preliminary testing on graphite and diamond successfully reproduce condensed phase structures. The models developed in this work, in principle, can retain most of the accuracy of quantum-based methods at any level of theory with relatively small training sets. Our efforts can thus allow for high throughput physical and chemical predictions with up to coupled-cluster accuracy for materials that are computationally intractable with standard approaches.

The image charge effect and vibron-assisted processes in Coulomb blockade transport: a first principles approach

Nanoscale ◽  
2015 ◽  
Vol 7 (45) ◽  
pp. 19231-19240 ◽  
Author(s):  
A. M. Souza ◽  
I. Rungger ◽  
U. Schwingenschlögl ◽  
S. Sanvito
Keyword(s):  
Quantum Transport ◽  
First Principles ◽  
Coulomb Blockade ◽  
Density Functional ◽  
Image Charge ◽  
Functional Theory ◽  
Master Equation Approach ◽  
Image Charge Effect ◽  
Coulomb Blockade Regime ◽  
Non Equilibrium Green’S Function

We present a combination of density functional theory and of both non-equilibrium Green's function formalism and a Master equation approach to accurately describe quantum transport in molecular junctions in the Coulomb blockade regime.

scholarly journals A new photodetector structure based on graphene nanomeshes: an ab initio study

2020 ◽  
Vol 11 ◽  
pp. 1036-1044
Author(s):  
Babak Sakkaki ◽  
Hassan Rasooli Saghai ◽  
Ghafar Darvish ◽  
Mehdi Khatir
Keyword(s):  
Infrared Detectors ◽  
Density Functional ◽  
Tight Binding ◽  
Optical Devices ◽  
Functional Theory ◽  
Semiconducting Properties ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
Non Equilibrium Green’S Function ◽  
Insight Into

Recent experiments suggest graphene-based materials as candidates in future electronic and optoelectronic devices. In this paper, we propose to investigate new photodetectors based on graphene nanomeshes (GNMs). Density functional theory (DFT) calculations are performed to gain insight into electronic and optical characteristics of various GNM structures. To investigate the device-level properties of GNMs, their current–voltage characteristics are explored by DFT-based tight-binding (DFTB) in combination with non-equilibrium Green’s function (NEGF) methods. Band structure analysis shows that GNMs have both metallic and semiconducting properties depending on the arrangements of perforations. Also, absorption spectrum analysis indicates attractive infrared peaks for GNMs with semiconducting characteristics, making them better photodetectors than graphene nanoribbon (GNR)-based alternatives. The results suggest that GNMs can be potentially used in mid-infrared detectors with specific detectivity values that are 100-fold that of graphene-based devices and 1000-fold that of GNR-based devices. Hence, the special properties of graphene combined with the quantum feathers of the perforation makes it suitable for optical devices.

scholarly journals Reduced k-points based computationally efficient band structure approach for UTB device simulation

2021 ◽  
Author(s):  
Ravi Solanki ◽  
Nalin Vilochan Mishra ◽  
Aditya S Medury
Keyword(s):  
Band Structure ◽  
Density Functional ◽  
Tight Binding ◽  
Computational Time ◽  
Thin Body ◽  
Computationally Efficient ◽  
Wide Range ◽  
Full Band ◽  
Consistent Solution ◽  
Full Band Structure

The accurate calculation of channel electrostatics parameters, such as charge density and potential, in ultra-thin body (UTB) devices requires self-consistent solution of the Poisson’s equation and the full band structure, which is channel material and thickness dependent. For cubic crystals like silicon, the semi-empirical sp3d5s* tight-binding (TB) model is preferred in device simulations, over the density functional theory, to obtain the full band structure because of being computationally less intensive and equally accurate. However, the computational time of the TB model scales non-linearly with the channel thickness and becomes cumbersome for silicon, beyond 5 nm, primarily because of the increasing size of the TB hamiltonian that needs to be solved over the entire k-space, in the irreducible Brillouin zone. In this work, we precisely identify those k-points corresponding to the energies close to the band minima, where the Fermi-Dirac probability significantly affects electrostatics parameters. This enables us to demonstrate a computationally efficient approach based on solving the hamiltonian only on those reduced number of k-points. The rigorous benchmarking of the channel electrostatics parameters obtained from this approach is performed with results from accurate full band structure simulations showing excellent agreement over a wide range of channel thicknesses, oxide thicknesses, device temperatures and different channel orientations. By showing that the approach presented in this work is computationally efficient, besides being accurate, regardless of the number of atomic layers, we demonstrate its applicability for simulating UTB devices.

scholarly journals Density functional tight binding

2014 ◽  
Vol 372 (2011) ◽  
pp. 20120483 ◽  
Author(s):  
Marcus Elstner ◽  
Gotthard Seifert
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Taylor Series Expansion ◽  
State Density ◽  
Chemical Hardness ◽  
Computationally Efficient ◽  
Third Order ◽  
Functional Theory ◽  
Basic Principles ◽  
Efficient Representation

This paper reviews the basic principles of the density-functional tight-binding (DFTB) method, which is based on density-functional theory as formulated by Hohenberg, Kohn and Sham (KS-DFT). DFTB consists of a series of models that are derived from a Taylor series expansion of the KS-DFT total energy. In the lowest order (DFTB1), densities and potentials are written as superpositions of atomic densities and potentials. The Kohn–Sham orbitals are then expanded to a set of localized atom-centred functions, which are obtained for spherical symmetric spin-unpolarized neutral atoms self-consistently. The whole Hamilton and overlap matrices contain one- and two-centre contributions only. Therefore, they can be calculated and tabulated in advance as functions of the distance between atomic pairs. The second contributions to DFTB1, the DFT double counting terms, are summarized together with nuclear repulsion energy terms and can be rewritten as the sum of pairwise repulsive terms. The second-order (DFTB2) and third-order (DFTB3) terms in the energy expansion correspond to a self-consistent representation, where the deviation of the ground-state density from the reference density is represented by charge monopoles only. This leads to a computationally efficient representation in terms of atomic charges (Mulliken), chemical hardness (Hubbard) parameters and scaled Coulomb laws. Therefore, no additional adjustable parameters enter the DFTB2 and DFTB3 formalism. The handling of parameters, the efficiency, the performance and extensions of DFTB are briefly discussed.

Simulation and fabrication of an ammonia gas sensor based on PEDOT:PSS

Sensor Review ◽  
2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mokhtar Aarabi ◽  
Alireza Salehi ◽  
Alireza Kashaninia
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
Transport Properties ◽  
Quantum Transport ◽  
Density Functional ◽  
Function Method ◽  
Molecular Adsorption ◽  
Functional Theory ◽  
Content Type ◽  
Non Equilibrium Green’S Function

Purpose The purpose of this study is use to density functional theory (DFT) to investigate the molecular adsorption by PEDOT:PSS for different doping levels. DFT calculations are performed using the SIESTA code. In addition, the non-equilibrium Green’s function method is used within the TranSIESTA code to determine the quantum transport properties of molecular nanodevices. Design/methodology/approach Density functional theory (DFT) is used to investigate the molecular adsorption by PEDOT:PSS for different doping levels. DFT calculations are performed using the SIESTA code. In addition, the non-equilibrium Green’s function method is used within the TranSIESTA code to determine the quantum transport properties of molecular nanodevices. Findings Simulation results show very good sensitivity of Pd-doped PEDOT:PSS to ammonia, carbon dioxide and methane, so this structure cannot be used for simultaneous exposure to these gases. Silver-doped PEDOT:PSS structure provides a favorable sensitivity to ammonia in addition to exhibiting a better selectivity. If the experiment is repeated, the sensitivity is increased for a larger concentration of the applied gas. However, the sensitivity will decrease at a higher ratio than smaller concentrations of gas. Originality/value The advantages of the proposed sensor are its low-cost implementation and simple fabrication process compared to other sensors. Moreover, the proposed sensor exhibits appropriate sensitivity and repeatability at room temperature.

scholarly journals Finite-Temperature Single Molecule Vibrational Dynamics from Combined Density Functional Tight Binding Extended Lagrangian Dynamics Simulations and Time Series Analysis

2020 ◽  
Vol 20 (6) ◽  
pp. 201-212
Author(s):  
Bojana Koteska ◽  
Anastas Mishev ◽  
Ljupco Pejov
Keyword(s):  
Molecular Dynamics ◽  
Time Series ◽  
Single Molecule ◽  
Density Functional ◽  
Tight Binding ◽  
Range Data ◽  
Computationally Efficient ◽  
Vibrational Dynamics ◽  
Wide Range ◽  
Dynamics Simulations

AbstractCombining a computationally efficient and affordable molecular dynamics approach, based on atom-centered density matrix propagation scheme, with the density functional tight binding semiempirical quantum mechanics, we study the vibrational dynamics of a single molecule at series of finite temperatures, spanning quite wide range. Data generated by molecular dynamics simulations are further analyzed and processed using time series analytic methods, based on correlation functions formalism, leading to both vibrational density of states spectra and infrared absorption spectra at finite temperatures. The temperature-induced dynamics in structural intramolecular parameters is correlated to the observed changes in the spectral regions relevant to molecular detection. In particular, we consider a case when an intramolecular X-H stretching vibrational states are notably dependent on the intramolecular torsional degree of freedom, the dynamics of which is, on the other hand, strongly temperature-dependent.

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