arXiv subjects

Joseph E. Subotnik

Publications and source records attributed to Joseph E. Subotnik.

79 records · Page 5Linked to original sources

arXiv2018

Ehrenfest+R Dynamics II: A Semiclassical QED Framework for Raman Scattering

In a previous paper, we introduced Ehrenfest+R dynamics for a two-level system and showed how spontaneous emission can be heuristically included such that, after averaging over an ensemble of Ehrenfest+R trajectories, one can recover both coherent and incoherent electromagnetic fields. In the present paper, we now show that Ehrenfest+R dynamics can also correctly describe Raman scattering, whose features are completely absent from standard Ehrenfest dynamics. Ehrenfest+R dynamics appear to be quantitatively accurate both for resonant and off-resonant Raman signals, as compared with Kramers-Heisenberg-Dirac (KHD) theory.

physics.chem-ph↗

arXiv2018

A universal approach to quantum thermodynamics in the strong coupling regime

We present a protocol for the study of the dynamics and thermodynamics of quantum systems strongly coupled to a bath and subject to an external modulation. Our protocol quantifies the evolution of the system-bath composite by expanding the full density matrix as a series in the powers of the modulation rate, from which the functional form of work, heat and entropy rates can be obtained. Under slow driving, thermodynamic laws are established. The entropy production rate is positive and is found to be related to the excess work dissipated by friction, at least up to second order in the driving speed. As an example of the present methodology, we reproduce the results for the quantum thermodynamics of the driven resonance level model. We also emphasize that our formalism is quite general and allows for electron-electron interactions, which can give rise to exotic Kondo resonances appearing in thermodynamic quantities.

cond-mat.stat-mech↗

arXiv2018

Configuration Interaction Singles with Spin-Orbit Coupling: Constructing Spin-Adiabatic States and Their Analytical Nuclear Gradients

For future use in modeling photoexcited dynamics and intersystem crossing, we calculate spin-adiabatic states and their analytical nuclear gradients within CIS the- ory. These energies and forces should be immediately useful for surface hopping dynamics, which are natural within an adiabatic framework. The resulting code has been implemented within the Q-Chem software and preliminary results suggest that the additional cost of including SOC within the singles-singles block is not large.

physics.chem-ph↗

arXiv2018

The universality of electronic friction II: Equivalence of the quantum-classical Liouville equation approach with von Oppen's nonequilibrium Green's function methods out of equilibrium

In a recent publication [W. Dou, G. Miao, and J. E. Subotnik, Phys. Rev. Lett. 119, 046001 (2017)], using the quantum-classical Liouville equation (QCLE), we derived a very general form for the electronic friction felt by a molecule moving near one or many metal surfaces. Moreover, we have already proved the equivalence of the QCLE electronic friction with the Head-Gordon--Tully model as well as a generalized version of von Oppen's nonequilibrium Green's function (NEGF) method at equilibrium [W. Dou and J. E. Subotnik, Phys. Rev. B 96, 104305 (2017)]. In the present paper, we now further prove the equivalence between the QCLE friction and the NEGF friction for the case of multiple metal surfaces and an out-of-equilibrium electronic current. The present results conclude our recent claim that there is only one universal electronic friction tensor arising from the Born-Oppenheimer approximation.

cond-mat.mes-hall↗

arXiv2018

Mixed Quantum-Classical Electrodynamics: Understanding Spontaneous Decay and Zero Point Energy

The dynamics of an electronic two-level system coupled to an electromagnetic field are simulated explicitly for one and three dimensional systems through semiclassical propagation of the Maxwell-Liouville equations. We consider three flavors of mixed quantum-classical dynamics: the classical path approximation (CPA), Ehrenfest dynamics, and symmetrical quantum-classical (SQC) dynamics. The CPA fails to recover a consistent description of spontaneous emission. A consistent "spontaneous" emission can be obtained from Ehrenfest dynamics--provided that one starts in an electronic superposition state. Spontaneous emission is always obtained using SQC dynamics. Using the SQC and Ehrenfest frameworks, we further calculate the dynamics following an incoming pulse, but here we find very different responses: SQC and Ehrenfest dynamics deviate sometimes strongly in the calculated rate of decay of the transient excited state. Nevertheless, our work confirms the earlier observations by W. Miller [J. Chem. Phys. 69, 2188-2195, 1978] that Ehrenfest dynamics can effectively describe some aspects of spontaneous emission and highlights new possibilities for studying light-matter interactions with semiclassical mechanics.

physics.optics↗

arXiv2017

Born-Oppenheimer Dynamics, Electronic Friction, and the Inclusion of Electron-Electron Interactions

We present a universal expression for the electronic friction as felt by a set of classical nuclear degrees of freedom (DoF's) coupled to a manifold of quantum electronic DoF's; no assumptions are made regarding the nature of the electronic Hamiltonian and electron-electron repulsions are allowed. Our derivation is based on a quantum-classical Liouville equation (QCLE) for the coupled electronic-nuclear motion, followed by an adiabatic approximation whereby electronic transitions are assumed to equilibrate faster than nuclear movement. The resulting form of friction is completely general, but does reduce to previously published expressions for the quadratic Hamiltonian (i.e. Hamiltonians without electronic correlation). At equilibrium, the second fluctuation-dissipation theorem is satisfied and the frictional matrix is symmetric. To demonstrate the importance of electron-electron correlation, we study electronic friction within the Anderson-Holstein model, where a proper treatment of electron-electron interactions shows signatures of a Kondo resonance and a mean-field treatment is completely inadequate.

cond-mat.mtrl-sci↗

arXiv2016

Electronic friction near metal surfaces: a case where molecule-metal couplings depend on nuclear coordinates

We derive an explicit form for the electronic friction as felt by a molecule near a metal surface for the general case that molecule-metal couplings depend on nuclear coordinates. Our work generalizes a previous study by von Oppen et al [Beilstein Journal of Nanotechnology, 3, 144, 2012], where we now go beyond the Condon approximation (i.e. molecule-metal couplings are not held constant). Using a non-equilibrium Green's function formalism in the adiabatic limit, we show that fluctuating metal-molecule couplings lead to new frictional damping terms and random forces, plus a correction to the potential of mean force. Numerical tests are performed and compared with a modified classical master equation; our results indicate that violating the Condon approximation can have a large effect on dynamics.

physics.chem-ph↗