Charge nonconservation of molecular devices in the presence of a nonlocal potential

Lai, Lu; Chen, J.; Liu, Q. H.; Yu, Yabin

doi:10.1103/physrevb.100.125437

Cited by 3 publications

(4 citation statements)

References 49 publications

(53 reference statements)

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“…We calculated the current density in a cylindrical coordinate system, which allow us to color the arrows by the relative cylindrical vectorcomponent 9 " |9 ;⃑| . The conversion from cartesian to cylindrical coordinates is trivial, and is included for reference in SI part H. Finally, as we and other have recently noted, 45,56,[97][98][99][100] ballistic current density calculations can have serious issues with current conservation over the molecule due to using a finite local basis set and approximated core-potentials; we provide some examples of this problem in SI part G.…”

Section: Methodsmentioning

confidence: 99%

“…The conversion from Cartesian to cylindrical coordinates is trivial and is included for reference in the Supporting Information part H. Finally, as we and others have recently noted, ,,− ballistic current density calculations can have serious issues with current conservation over the molecule due to using a finite local basis set and approximated core potentials; we provide some examples of this problem in the Supporting Information part G.…”

Section: Methodsmentioning

confidence: 99%

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Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

2020

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The one-dimensional carbon allotrope carbyne, a linear chain of sp-hybridized carbon atoms, is predicted to exist in a polyynic and a cumulenic structure. While molecular forms of carbyne have been extensively characterized, the structural nature is hard to determine for many linear carbon wires that are made in-situ during pulling experiments. Here, we show that cumulenes and polyynes have distinctively different low-bias conductance profiles under axial torsion. We analyze the change of the electronic structure, Landauer transmission, and ballistic current density of the three types of closed-shell molecular carbynes as a function of the torsion angle. Both polyynic, odd-carbon cumulenic, and even-carbon cumulenic carbon wires exhibit helical frontier molecular orbitals when the end-groups are not in a co-planar configuration. This helical conjugation effect gives rise to strong ring current patterns around the linear wires. Only the transmission of even-carbon polyynic wires follows the well-known cosine-squared law with axial torsion that is also seen in biphenyl-type systems. Notably, the transmission of even-carbon cumulenic carbon wires rises with axial torsion from co-planar towards perpendicular orientation of the end-groups. The three distinct transmission profiles of polyynes, odd-carbon cumulenes, and even-carbon cumulenes may allow for experimental identification of the structural nature of linear carbon wires. Their different electron transport properties under axial torsion furthermore underline that, in the molecular limit of carbyne, three different subclasses of linear carbon wires exist. File list (3)download file view on ChemRxiv torsion_chemrxiv3.pdf (6.17 MiB) download file view on ChemRxiv SI_chemrxiv3.pdf (9.24 MiB) download file view on ChemRxiv files.zip (21.38 MiB)

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

2020

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“…The next step, however, is often to introduce approximations and effective models with non-local interactions. Furthermore, even in the original local theory, quantum anomalies may occur after renormalization, spoiling the symmetry and conservation properties of the original Hamiltonian [8][9][10]. In most approaches to quantum transport there is no attempt to compute the wavefunction of tunneling particles in the barrier.…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic Signatures of Possible Charge Anomalies in Tunneling

Minotti

Modanese

2022

Quantum Reports

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We reconsider some well-known tunneling processes from the point of view of Aharonov-Bohm electrodynamics, a unique extension of Maxwell’s theory which admits charge-current sources that are not locally conserved. In particular we are interested into tunneling phenomena having relatively long range (otherwise the non-Maxwellian effects become irrelevant, especially at high frequency) and involving macroscopic wavefunctions and coherent matter, for which it makes sense to evaluate the classical e.m. field generated by the tunneling particles. For some condensed-matter systems, admitting discontinuities in the probability current is a possible way of formulating phenomenological models. In such cases, the Aharonov-Bohm theory offers a logically consistent approach and allows to derive observable consequences. Typical e.m. signatures of the failure of local conservation are at high frequency the generation of a longitudinal electric radiation field, and at low frequency a small effect of “missing” magnetic field. Possible causes of this failure are instant tunneling and phase slips in superconductors. For macroscopic quantum systems in which the phase-number uncertainty relation ΔNΔφ∼1 applies, the expectation value of the anomalous source I=∂tρ+∇·j has quantum fluctuations, thus becoming a random source of weak non-Maxwellian fields.

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“…The recourse to the NEGF-DFT formalism is necessary in order to take into account the contribution of the inner atomic shells. In principle a full quantum field theory of the system, if it can be formulated in a standard way including all the internal electrons, would yield a conserved bare current; in practice, such a formulation does not exist for realistic systems [3], and even if it could be achieved, it cannot be excluded that it needs to be renormalized, giving rise to quantum anomalies (effective breaking of symmetries and local conservation properties of the bare theory, like for the ABJ anomaly in condensed matter [4,5]).…”

Section: Introductionmentioning

confidence: 99%

Are Current Discontinuities in Molecular Devices Experimentally Observable?

Minotti

Modanese

2021

Symmetry

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An ongoing debate in the first-principles description of conduction in molecular devices concerns the correct definition of current in the presence of non-local potentials. If the physical current density ??j=(−ieℏ/2m)(Ψ*∇Ψ−Ψ∇Ψ*) is not locally conserved but can be re-adjusted by a non-local term, which current should be regarded as real? Situations of this kind have been studied for example, for currents in saturated chains of alkanes, silanes and germanes, and in linear carbon wires. We prove that in any case the extended Maxwell equations by Aharonov-Bohm give the e.m. field generated by such currents without any ambiguity. In fact, the wave equations have the same source terms as in Maxwell theory, but the local non-conservation of charge leads to longitudinal radiative contributions of E, as well as to additional transverse radiative terms in both E and B. For an oscillating dipole we show that the radiated electrical field has a longitudinal component proportional to ωP^, where P^ is the anomalous moment ∫I^(x)xd3x and I^ is the space-dependent part of the anomaly ?I=∂tρ+∇·j. For example, if a fraction η of a charge q oscillating over a distance 2a lacks a corresponding current, the predicted maximum longitudinal field (along the oscillation axis) is EL,max=2ηω2qa/(c2r). In the case of a stationary current in a molecular device, a failure of local current conservation causes a “missing field” effect that can be experimentally observable, especially if its entity depends on the total current; in this case one should observe at a fixed position changes in the ratio B/i in dependence on i, in contrast with the standard Maxwell equations. The missing field effect is confirmed by numerical solutions of the extended equations, which also show the spatial distribution of the non-local term in the current.

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Charge nonconservation of molecular devices in the presence of a nonlocal potential

Cited by 3 publications

References 49 publications

Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

Three Distinct Torsion Profiles of Electronic Transmission through Linear Carbon Wires

Electromagnetic Signatures of Possible Charge Anomalies in Tunneling

Are Current Discontinuities in Molecular Devices Experimentally Observable?

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