Showing papers on "Ground state published in 2016"
TL;DR: A kinetic theory of elementary excitations is proposed and an exact expression for the expectation values of the charge currents in a generic stationary state is unveiled for the nonequilibrium time evolution of piecewise homogeneous states in the XXZ spin-1/2 chain.
Abstract: We consider the nonequilibrium time evolution of piecewise homogeneous states in the XXZ spin-1/2 chain, a paradigmatic example of an interacting integrable model. The initial state can be thought of as the result of joining chains with different global properties. Through dephasing, at late times, the state becomes locally equivalent to a stationary state which explicitly depends on position and time. We propose a kinetic theory of elementary excitations and derive a continuity equation which fully characterizes the thermodynamics of the model. We restrict ourselves to the gapless phase and consider cases where the chains are prepared: (1) at different temperatures, (2) in the ground state of two different models, and (3) in the "domain wall" state. We find excellent agreement (any discrepancy is within the numerical error) between theoretical predictions and numerical simulations of time evolution based on time-evolving block decimation algorithms. As a corollary, we unveil an exact expression for the expectation values of the charge currents in a generic stationary state.
639 citations
TL;DR: The findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms.
Abstract: The ground-state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero-point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si-C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC-MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms.
404 citations
TL;DR: In this article, coherent Rydberg dressing was used to implement a two-dimensional synthetic spin lattice, where ground state atoms were coupled to Rydgberg states via off-resonant laser coupling.
Abstract: The control of long-range interactions is an essential ingredient for the study of exotic phases of matter using atoms in optical lattices. Such control is demonstrated using Rydberg dressing: the coupling of ground state atoms to Rydberg states. Ultracold atoms in optical lattices are ideal to study fundamentally new quantum many-body systems1,2 including frustrated or topological magnetic phases3,4 and supersolids5,6. However, the necessary control of strong long-range interactions between distant ground state atoms has remained a long-standing goal. Optical dressing of ground state atoms via off-resonant laser coupling to Rydberg states is one way to tailor such interactions5,6,7,8. Here we report the realization of coherent Rydberg dressing to implement a two-dimensional synthetic spin lattice. Our single-atom-resolved interferometric measurements of the many-body dynamics enable the microscopic probing of the interactions and reveal their highly tunable range and anisotropy. Our work marks the first step towards the use of laser-controlled Rydberg interactions for the study of exotic quantum magnets3,4,9 in optical lattices.
334 citations
TL;DR: The results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultrACold bosonic molecules with strong dipolar interactions.
Abstract: A new bosonic species of ultracold alkali heteromolecule with a considerable electric dipole moment has been cooled to its vibrational ground state.
298 citations
TL;DR: In this article, a review of the most recent achievements in the experimental and theoretical studies of the non-equilibrium electronic, optical, structural and magnetic properties of correlated materials is presented.
Abstract: In the last two decades, non-equilibrium spectroscopies have evolved from avant-garde studies to crucial tools for expanding our understanding of the physics of strongly correlated materials. The possibility of obtaining simultaneously spectroscopic and temporal information has led to insights that are complementary to (and in several cases beyond) those attainable by studying the matter at equilibrium. Multiple phase transitions and new orders arising from competing interactions are benchmark examples where the interplay among electrons, lattice, and spin dynamics can be disentangled because of the different timescales that characterize the recovery of the initial ground state. The nature of the broken-symmetry phases and of the bosonic excitations that mediate the electronic interactions, eventually leading to superconductivity or other exotic states, can be revealed by observing the sub-picosecond dynamics of impulsively excited states. Recent experimental developments have made possible to monitor the time-evolution of both the single-particle and collective excitations under extreme conditions, such as those arising from strong and selective photo-stimulation.
Here, we review the most recent achievements in the experimental and theoretical studies of the non-equilibrium electronic, optical, structural and magnetic properties of correlated materials. The focus will be mainly on the prototypical case of correlated oxides that exhibit unconventional superconductivity or other exotic phases, even though the discussion will extend also to other topical systems. The necessity of extending the actual experimental capabilities and the numerical and analytic tools to microscopically treat the non-equilibrium phenomena beyond the simple phenomenological approaches represents one of the most challenging new frontier in physics.
243 citations
TL;DR: In this paper, the formation of a macro-droplet state in an ultracold bosonic gas of erbium atoms with strong dipolar interactions was reported, and the authors quantitatively proved that quantum fluctuations stabilize the gas far beyond the instability threshold imposed by mean-field interactions.
Abstract: In a joint experimental and theoretical effort, we report on the formation of a macro-droplet state in an ultracold bosonic gas of erbium atoms with strong dipolar interactions. By precise tuning of the s-wave scattering length below the so-called dipolar length, we observe a smooth crossover of the ground state from a dilute Bose-Einstein condensate (BEC) to a dense macro-droplet state of more than $10^4$ atoms. Based on the study of collective excitations and loss features, we quantitative prove that quantum fluctuations stabilize the ultracold gas far beyond the instability threshold imposed by mean-field interactions. Finally, we perform expansion measurements, showing the evolution of the normal BEC towards a three-dimensional self-bound state and show that the interplay between quantum stabilization and three-body losses gives rise to a minimal expansion velocity at a finite scattering length.
240 citations
TL;DR: In this paper, the antiferromagnetic (AFM) skyrmion has been shown to move straightly over long distance, benefiting from the absence of the SkHE.
Abstract: Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.
238 citations
TL;DR: It is shown that the superfluid weight can be large even for an isolated and strictly flat band, proportional to the interaction strength and to the quantum metric, a band structure quantity derived solely from the flat-band Bloch functions.
Abstract: The ground state and transport properties of the Lieb lattice flat band in the presence of an attractive Hubbard interaction are considered. It is shown that the superfluid weight can be large even for an isolated and strictly flat band. Moreover the superfluid weight is proportional to the interaction strength and to the quantum metric, a band structure quantity derived solely from the flat-band Bloch functions. These predictions are amenable to verification with ultracold gases and may explain the anomalous behavior of the superfluid weight of high-${T}_{c}$ superconductors.
220 citations
TL;DR: The first experimental observation of the torsional vibration of an optically levitated nonspherical nanoparticle in vacuum is reported, achieved by utilizing the coupling between the spin angular momentum of photons and the torrent vibration of a nonspherial nanoparticle whose polarizability is a tensor.
Abstract: Researchers characterize the rotational jiggling of an optically levitated nanoparticle, showing how this motion could be cooled to its quantum ground state.
209 citations
TL;DR: The promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3 is discussed, and indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field are found.
Abstract: Using quantum chemistry calculations we shed fresh light on the electronic structure and magnetic properties of RuCl3, a proposed realization of the honeycomb Kitaev spin model. It is found that the nearest-neighbor Kitaev exchange K is weaker than in 5d5 Ir oxides but still larger than other effective spin couplings. The electronic-structure computations also indicate a ferromagnetic K in the halide, which is supported by a detailed analysis of the field-dependent magnetization. From exact-diagonalization calculations for extended Kitaev-Heisenberg Hamiltonians we additionally find that a transition from zigzag order to a spin-liquid ground state can be induced in RuCl3 with external magnetic field.
203 citations
TL;DR: It is shown that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge- transfer energy in line with recent models interpreting the metal–insulator transition in terms of bond disproportionation.
Abstract: The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.
TL;DR: In this paper, the authors considered the existence of ground state sign-changing solutions for a class of Kirchhoff-type problems (0.1) and proved that the energy of the ground state solution is strictly larger than twice that of the non-Neighari-type ground state solutions.
TL;DR: The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment.
Abstract: Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e^{+}e^{-} pairs produced in ^{8}Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, ^{8}Be^{*}→^{8}Be X, and then decays through X→e^{+}e^{-}. The X boson mediates a fifth force with a characteristic range of 12 fm and has millicharged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment.
TL;DR: In this article, the ground-state phase diagram of the frustrated Hubbard and frustrated Hubbard models on the square lattice with density matrix embedding theory is computed using clusters of up to 16 sites, and an error model is provided to estimate the reliability of the computations and complexity of the physics at different points in the diagram.
Abstract: We compute the ground-state phase diagram of the Hubbard and frustrated Hubbard models on the square lattice with density matrix embedding theory using clusters of up to 16 sites. We provide an error model to estimate the reliability of the computations and complexity of the physics at different points in the diagram. We find superconductivity in the ground state as well as competition between inhomogeneous charge, spin, and pairing states at low doping. The estimated errors in the study are below T_c in the cuprates and on the scale of contributions in real materials that are neglected in the Hubbard model.
TL;DR: In this paper, the ground state of dipolar Bose-Einstein condensates (BEC) is studied in the regimes of three different phases, where a characteristic growth of the peak density of the BEC is predicted when the dipolar quantum droplets are formed.
Abstract: The ground state of dipolar Bose-Einstein condensates (BEC) is studied in the regimes of three different phases, where a characteristic growth of the peak density of the BEC is predicted when the dipolar quantum droplets are formed.
TL;DR: It is established that iSF can occur via a direct coupling mechanism that is independent of CT states, and it is shown that a near-degeneracy in electronic state energies induced by vibronic coupling to intramolecular modes of the covalent dimer allows for strong mixing between the correlated triplet pair state and the local excitonic state, despite weak direct coupling.
Abstract: Interest in materials that undergo singlet fission (SF) has been catalyzed by the potential to exceed the Shockley–Queisser limit of solar power conversion efficiency. In conventional materials, the mechanism of SF is an intermolecular process (xSF), which is mediated by charge transfer (CT) states and depends sensitively on crystal packing or molecular collisions. In contrast, recently reported covalently coupled pentacenes yield ∼2 triplets per photon absorbed in individual molecules: the hallmark of intramolecular singlet fission (iSF). However, the mechanism of iSF is unclear. Here, using multireference electronic structure calculations and transient absorption spectroscopy, we establish that iSF can occur via a direct coupling mechanism that is independent of CT states. We show that a near-degeneracy in electronic state energies induced by vibronic coupling to intramolecular modes of the covalent dimer allows for strong mixing between the correlated triplet pair state and the local excitonic state, d...
TL;DR: In this article, the authors present a variational optimization scheme, in which the energy is minimized in an iterative way by sweeping over all the tensors in the ansatz, in a similar spirit as done in the density-matrix renormalization group method.
Abstract: An infinite projected entangled-pair state (iPEPS) is a powerful variational tensor network ansatz for two-dimensional ground states in the thermodynamic limit, and can be seen as a natural generalization of a matrix-product state to two dimensions. One of the main challenges in iPEPS simulations is the optimization of the tensors, i.e., finding the optimal variational parameters, in order to have the best representation of the ground state of a given Hamiltonian. The author presents a variational optimization scheme, in which the energy is minimized in an iterative way by sweeping over all the tensors in the ansatz, in a similar spirit as done in the density-matrix renormalization group method. Benchmark results for challenging problems are presented that show that the variational scheme yields considerably more accurate results than the previously best imaginary-time evolution algorithm, with a similar computational cost and with a faster convergence towards the ground state.
TL;DR: In this article, the ground state properties of a trapped dipolar condensate under the influence of quantum fluctuations were investigated and it was shown that this system can undergo a phase transition from a low-density Condensate state to a high-density droplet state, which is stabilized by quantum fluctuations.
Abstract: We consider the ground state properties of a trapped dipolar condensate under the influence of quantum fluctuations. We show that this system can undergo a phase transition from a low density condensate state to a high density droplet state, which is stabilized by quantum fluctuations. The energetically favored state depends on the geometry of the confining potential, the number of atoms, and the two-body interactions. We develop a simple variational ansatz and validate it against full numerical solutions. We produce a phase diagram for the system and present results relevant to current experiments with dysprosium and erbium condensates.
TL;DR: This work considers two separate atoms interacting with a single-mode optical or microwave resonator and shows that there exists a resonant coupling between one photon and two atoms, via intermediate virtual states connected by counterrotating processes.
Abstract: We consider two separate atoms interacting with a single-mode optical or microwave resonator. When the frequency of the resonator field is twice the atomic transition frequency, we show that there exists a resonant coupling between one photon and two atoms, via intermediate virtual states connected by counterrotating processes. If the resonator is prepared in its one-photon state, the photon can be jointly absorbed by the two atoms in their ground state which will both reach their excited state with a probability close to one. Like ordinary quantum Rabi oscillations, this process is coherent and reversible, so that two atoms in their excited state will undergo a downward transition jointly emitting a single cavity photon. This joint absorption and emission process can also occur with three atoms. The parameters used to investigate this process correspond to experimentally demonstrated values in circuit quantum electrodynamics systems.
TL;DR: Duo solves the Schrodinger equation for the motion of the nuclei not only for the simple case of uncoupled, isolated electronic states but also for the general case of an arbitrary number and type of couplings between electronic states.
TL;DR: The recently developed particle–particle random-phase approximation is used in combination with a diradical analysis to unveil the nature of higher acenes' ground- and electronic excited states, and the excitation energies are presented.
Abstract: Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle–particle random-phase approximation calculation. The 1 A g ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state 3 B 2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state 1 B 2u is a zwitterionic state to the short axis. The excited 1 A g state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the 1 B 2u and excited 1 A g states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved.
TL;DR: It is shown that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.
Abstract: Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.
TL;DR: This work demonstrates individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as a tuning of couplings between ions within experimental sequences, paves the way towards a quantum simulator of two-dimensional systems designed at will.
Abstract: A precisely controlled quantum system may reveal a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analogue quantum simulator that makes relevant observables, interactions and states of a quantum model accessible could permit insight into complex dynamics. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here, we operate two-dimensional arrays of three trapped ions in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 μm. In our approach, which is scalable to arbitrary two-dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as a tuning of couplings between ions within experimental sequences. Our work paves the way towards a quantum simulator of two-dimensional systems designed at will.
TL;DR: The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation.
Abstract: A fully polarizable implementation of the hybrid quantum mechanics/molecular mechanics approach is presented, where the classical environment is described through the AMOEBA polarizable force field. A variational formalism, offering a self-consistent relaxation of both the MM induced dipoles and the QM electronic density, is used for ground state energies and extended to electronic excitations in the framework of time-dependent density functional theory combined with a state specific response of the classical part. An application to the calculation of the solvatochromism of the pyridinium N-phenolate betaine dye used to define the solvent ET(30) scale is presented. The results show that the QM/AMOEBA model not only properly describes specific and bulk effects in the ground state but it also correctly responds to the large change in the solute electronic charge distribution upon excitation.
Book•
23 Aug 2016
TL;DR: Part I Electron-electron interaction, Part II Electronic ground state, Part III Single-particle excitations: Electrons and holes, Part IV Pair and collective excitations as discussed by the authors.
Abstract: Part I Electron-electron interaction.- Part II Electronic ground state.- Part III Single-particle excitations: Electrons and holes.- Part IV Pair and collective excitations.
TL;DR: In this article, the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of YbMgGaO 4 were presented, which was recently argued to be a promising candidate for a quantum spin liquid (QSL).
Abstract: We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of ${\mathrm{YbMgGaO}}_{4}$, which was recently argued to be a promising candidate for a quantum spin liquid (QSL). In a zero magnetic field, a large magnetic contribution of specific heat is observed, and exhibits a power-law temperature dependence (${C}_{m}\ensuremath{\sim}{T}^{0.74}$). On the contrary, we do not observe any significant contribution of thermal conductivity from magnetic excitations. In magnetic fields $H\ensuremath{\ge}6\text{ }\text{ }\mathrm{T}$, the exponential $T$ dependence of ${C}_{m}$ and the enhanced thermal conductivity indicate a magnon gap of the fully polarized state. The absence of magnetic thermal conductivity at the zero field in this QSL candidate puts a strong constraint on the theories of its ground state.
TL;DR: In this paper, a restricted access to a conical intersection (RACI) model was introduced to explain aggregation induced emission (AIE) in the prototypical dimethyl tetraphenylsilole (DMTPS) molecule.
Abstract: The mechanism behind aggregation induced emission (AIE) in the prototypical dimethyl tetraphenylsilole (DMTPS) molecule is investigated with ab initio calculations combining the CASSCF and CASPT2 methods with time-dependent DFT. DMTPS is AIE-active because it is strongly fluorescent in the aggregate phase but only weakly in solution. Based on the results, we introduce a restricted access to a conical intersection (RACI) model to explain AIE in DMTPS. According to the RACI model, excited DMTPS in solution can decay to the ground state because there is an energetically available conical intersection, and this explains the weak fluorescence observed experimentally. The reaction coordinate to the intersection involves mainly a twist of the silole ring and a flapping motion of the phenyl substituents. The behaviour in the aggregate phase is simulated by carrying out calculations of one excited DMTPS molecule embedded in a crystal. Because of steric effects, the conical intersection in the crystal is not accessible energetically, and the molecule fluoresces. Thus, the different energy required to access the conical intersection with the ground state in solution and in the crystal explains the AIE phenomenon. Our results are in good agreement with the experimental photophysical properties (absorption and emission wavelength) of DMTPS. They are also in line with recent experimental results for a phosphole analogue of DMTPS showing that fusion of a benzene ring to the phosphole ring increases the lifetime of the excited state in solution (F. Bu, E. Wang, Q. Peng, R. Hu, A. Qin, Z. Zhao and B. Z. Tang, Chem. – Eur. J., 2015, 21, 4440). The present work, together with our previous study on diphenyl dibenzofulvene (Q. Li and L. Blancafort, Chem. Commun., 2013, 49, 5966), suggests that RACI must be quite a general model to explain AIE in medium sized molecules. It is also consistent with the restriction of intramolecular motion (RIM) mechanism introduced recently to explain AIE, since the intramolecular motions responsible for AIE are those leading to the intersection. Knowledge of the reaction coordinate to access the intersection provides useful guidelines for the design of more efficient luminescent compounds.
TL;DR: In this article, the authors compute grain boundary (GB) properties for a large set of GBs in bcc transition metals with a special focus on W, Mo and Fe using ab initio density functional theory (DFT) and semi-empirical second nearest neighbor modified embedded atom method (2NN-MEAM) potentials.
Abstract: In this study, we compute grain boundary (GB) properties for a large set of GBs in bcc transition metals with a special focus on W, Mo and Fe using ab initio density functional theory (DFT) and semi-empirical second nearest neighbour modified embedded atom method (2NN-MEAM) potentials. The GB properties include GB energies, surface energies, GB excess volume and work of separation, which we analyse and then compare to experimental data. We find that the used 2NN-MEAM potentials can predict general trends of GB properties, but do not always reproduce the GB ground state structure and energy found with DFT. In particular, our results explain the experimental finding that W and Mo prefer intergranular fracture, while other bcc metals prefer transgranular cleavage.
TL;DR: Real-time time-dependent functional theory (RT-TDDFT) as discussed by the authors directly propagates the electron density in the time domain by integrating the timedependent Kohn-Sham equations, in contrast to the popular linear response TDDFT matrix formulation that computes transition frequencies from a ground state reference.
Abstract: Real-time time-dependent functional theory (RT-TDDFT) directly propagates the electron density in the time domain by integrating the time-dependent Kohn–Sham equations. This is in contrast to the popular linear response TDDFT matrix formulation that computes transition frequencies from a ground state reference. RT-TDDFT is, therefore, a potentially powerful technique for modeling atto- to picosecond electron dynamics, including charge transfer pathways, the response to a specific applied field, and frequency dependent linear and nonlinear properties. However, qualitatively incorrect electron dynamics and time-dependent resonant frequencies can occur when perturbing the density away from the ground state due to the common adiabatic approximation. An overview of the RT-TDDFT method is provided here, including examples of some cases that lead to this qualitatively incorrect behavior. © 2016 Wiley Periodicals, Inc.
TL;DR: In this article, the effects of using thermal and quantum samplings are analyzed taking pyrrole as a test case, and it is shown that there are significant differences in the results obtained with each two approaches.
Abstract: Semiclassical simulations of spectrum and dynamics of complex molecules require statistical sampling of coordinates and momenta. The effects of using thermal and quantum samplings are analyzed taking pyrrole as a test case. It is shown that there are significant differences in the results obtained with each of these two approaches. Overall, quantum sampling based on a Wigner distribution renders superior results, comparing well to the experiments. Dynamics simulations based on surface hopping and ADC(2) reveal that pyrrole internal conversion to the ground state occurs not only through H-elimination path, but also through ring-distortion paths, which have been systematically neglected by diverse experimental setups. The analysis of the reaction paths also shows that the ionization potential varies by more than 5 eV between ionization of the excited state at the Franck-Condon region and at the intersections with the ground state. This feature may have major implications for time-resolved photoelectron spectroscopy. (c) 2015 Wiley Periodicals, Inc.