I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functionai theory （...I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functionai theory （DFT）. The DFT eigenvectors are then transformed into a set of maximaily localized Wannier functions （MLWFs） [N. Maxzari and D. Vanderbilt, Phys. Rev. B 56 （1997） 12847]. The MLWFs are used as a minimai basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green＇s function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green＇s function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires （Cu and Pt）. It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomie wire due to the contribution of d-orbitals at the Fermi energy,展开更多
This review deals with the nonequilibrium Green＇s function （NEGF） method applied to the problems of energy transport due to atomic vibrations （phonons）, primarily for small jtmction systems. We present a pedagogi...This review deals with the nonequilibrium Green＇s function （NEGF） method applied to the problems of energy transport due to atomic vibrations （phonons）, primarily for small jtmction systems. We present a pedagogical introduction to the subject, deriving some of the well-known results such as the Laudauer-like formula for heat current in ballistic systerms. The main aim of the review is to build the machinery of the method so that it can be applied to other situations, which are not directly treated here. In addition to the above, we consider a nmnber of applications of NEGF, not in routine model system calculations, but in a few new aspects showing the power and usefulness of the formalism. In partkaflar, we discuss the problems of multiple leads, coupled left-right-lead system, and system without a center. We also apply the method to the problem of full counting statisties. In the case of nonlinear svstems, we make general comments on the thermal expansion effect. phonon relaxation timv. and a certain class of mean-field approximations. Lastly, we examine the relationship between NEGF. reduced density matrix, and master equation approaches to thermal transport,展开更多
With the rapidly increasing integration density and power density in nanoscale electronic devices,the thermal management concerning heat generation and energy harvesting becomes quite crucial.Since phonon is the major...With the rapidly increasing integration density and power density in nanoscale electronic devices,the thermal management concerning heat generation and energy harvesting becomes quite crucial.Since phonon is the major heat carrier in semiconductors,thermal transport due to phonons in mesoscopic systems has attracted much attention.In quantum transport studies,the nonequilibrium Green’s function(NEGF)method is a versatile and powerful tool that has been developed for several decades.In this review,we will discuss theoretical investigations of thermal transport using the NEGF approach from two aspects.For the aspect of phonon transport,the phonon NEGF method is briefly introduced and its applications on thermal transport in mesoscopic systems including one-dimensional atomic chains,multi-terminal systems,and transient phonon transport are discussed.For the aspect of thermoelectric transport,the caloritronic effects in which the charge,spin,and valley degrees of freedom are manipulated by the temperature gradient are discussed.The time-dependent thermoelectric behavior is also presented in the transient regime within the partitioned scheme based on the NEGF method.展开更多
We investigate atomic and electronic structures of boron nanotubes （BNTs） by using the density functional theory （DFT）. The transport properties of BNTs with different diameters and chiralities are studied by the ...We investigate atomic and electronic structures of boron nanotubes （BNTs） by using the density functional theory （DFT）. The transport properties of BNTs with different diameters and chiralities are studied by the Keldysh nonequilibrium Green function （NEGF） method. It is found that the cohesive energies and conductances of BNTs decrease as their diameters decrease. It is more difficult to form （N, 0） tubes than （M, M） tubes when the diameters of the two kinds of tubes are comparable. However, the （N, 0） tubes have a higher conductance than the （M, M） tubes. When the BNTs are connected to gold electrodes, the coupling between the BNTs and the electrodes will affect the transport properties of tubes significantly.展开更多
基金Support from Ningbo Science Foundation under Grant No.2010A610179also from the Start-Up Fund and K.C.Wong Magna Fund in Ningbo University
文摘I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functionai theory （DFT）. The DFT eigenvectors are then transformed into a set of maximaily localized Wannier functions （MLWFs） [N. Maxzari and D. Vanderbilt, Phys. Rev. B 56 （1997） 12847]. The MLWFs are used as a minimai basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green＇s function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green＇s function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires （Cu and Pt）. It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomie wire due to the contribution of d-orbitals at the Fermi energy,
文摘This review deals with the nonequilibrium Green＇s function （NEGF） method applied to the problems of energy transport due to atomic vibrations （phonons）, primarily for small jtmction systems. We present a pedagogical introduction to the subject, deriving some of the well-known results such as the Laudauer-like formula for heat current in ballistic systerms. The main aim of the review is to build the machinery of the method so that it can be applied to other situations, which are not directly treated here. In addition to the above, we consider a nmnber of applications of NEGF, not in routine model system calculations, but in a few new aspects showing the power and usefulness of the formalism. In partkaflar, we discuss the problems of multiple leads, coupled left-right-lead system, and system without a center. We also apply the method to the problem of full counting statisties. In the case of nonlinear svstems, we make general comments on the thermal expansion effect. phonon relaxation timv. and a certain class of mean-field approximations. Lastly, we examine the relationship between NEGF. reduced density matrix, and master equation approaches to thermal transport,
基金the National Natural Science Foundation of China(Grant Nos.12074190,11975125,11890703,and 11874221).
文摘With the rapidly increasing integration density and power density in nanoscale electronic devices,the thermal management concerning heat generation and energy harvesting becomes quite crucial.Since phonon is the major heat carrier in semiconductors,thermal transport due to phonons in mesoscopic systems has attracted much attention.In quantum transport studies,the nonequilibrium Green’s function(NEGF)method is a versatile and powerful tool that has been developed for several decades.In this review,we will discuss theoretical investigations of thermal transport using the NEGF approach from two aspects.For the aspect of phonon transport,the phonon NEGF method is briefly introduced and its applications on thermal transport in mesoscopic systems including one-dimensional atomic chains,multi-terminal systems,and transient phonon transport are discussed.For the aspect of thermoelectric transport,the caloritronic effects in which the charge,spin,and valley degrees of freedom are manipulated by the temperature gradient are discussed.The time-dependent thermoelectric behavior is also presented in the transient regime within the partitioned scheme based on the NEGF method.
基金Project supported by the National Natural Science Foundation of China (Grant No 10774176)the National Basic Research Program of China (Grant Nos 2006CB806202 and 2006CB921305)the Shanghai Supercomputing Center,Chinese Academyof Sciences
文摘We investigate atomic and electronic structures of boron nanotubes （BNTs） by using the density functional theory （DFT）. The transport properties of BNTs with different diameters and chiralities are studied by the Keldysh nonequilibrium Green function （NEGF） method. It is found that the cohesive energies and conductances of BNTs decrease as their diameters decrease. It is more difficult to form （N, 0） tubes than （M, M） tubes when the diameters of the two kinds of tubes are comparable. However, the （N, 0） tubes have a higher conductance than the （M, M） tubes. When the BNTs are connected to gold electrodes, the coupling between the BNTs and the electrodes will affect the transport properties of tubes significantly.
