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A new diagrammatic quantum Monte Carlo approach is proposed to deal with the imaginary time propagator involving both dynamic disorder (i.e., electron–phonon interactions) and static disorder of local or nonlocal nature in a unified and numerically exact way. The establishment of the whole framework relies on a general reciprocal-space expression and a generalized Wick's theorem for the static disorder. Since the numerical cost is independent of the system size, various physical quantities, such as the thermally averaged coherence, Matsubara one-particle Green's function, and current autocorrelation function, can be efficiently evaluated in the thermodynamic limit (infinite in the system size). The validity and performance of the proposed approach are systematically examined in a broad parameter regime. This approach, combined with proper numerical analytic continuation methods and first-principles calculations, is expected to be a versatile tool toward the calculation of various transport properties, such as mobilities in realistic semiconductors involving multiple electronic energy bands, high-frequency optical and low-frequency acoustic phonons, different forms of dynamic and static disorders, and anisotropy. [ABSTRACT FROM AUTHOR]

The electron–phonon scattering plays a crucial role in determining the electronic, transport, optical, and thermal properties of materials. Here, we employ a non-Markovian stochastic Schrödinger equation (NMSSE) in momentum space, together with ab initio calculations for energy bands and electron–phonon interactions, to reveal the phonon-mediated ultrafast hole relaxation dynamics in the valence bands of monolayer black phosphorus. Our numerical simulations show that the hole can initially remain in the high-energy valence bands for more than 100 fs due to the weak interband scatterings, and its energy relaxation follows single-exponential decay toward the valence band maximum after scattering into low-energy valence bands. The total relaxation time of holes is much longer than that of electrons in the conduction band. This suggests that harnessing the excess energy of holes may be more effective than that of electrons. Compared to the semiclassical Boltzmann equation based on a hopping model, the NMSSE highlights the persistence of quantum coherence for a long time, which significantly impacts the relaxation dynamics. These findings complement the understanding of hot carrier relaxation dynamics in two-dimensional materials and may offer novel insights into harnessing hole energy in photocatalysis. [ABSTRACT FROM AUTHOR]

It has been widely recognized that plasmonic metal nanoparticles (MNPs) can enhance the power convention efficiency (PCE) of dye-sensitized solar cells (DSSCs). This enhancement is ascribed to the combined effects of plasmon decay, scattering, near-field enhancement, and exciting charge carriers in semiconductors through plasmon-induced resonance energy transfer (PIRET) and hot electron injection (HEI). PIRET and HEI processes appeared between MNPs, and semiconductors have been intensively investigated; however, it is not clear how the collaborative effect of PIRET and photon-induced direct and indirect electron transfer (PICT) occurred between plasmonic metals and dyes, and the interference of different charge separation channels (CSCs) starting from PIRET and PICT affects the PCE of DSSCs. This work aims to address these issues. We apply a model Hamiltonian method, which obviously includes both PIRET and PICT processes from Au MNP to dye molecules and incorporates the dye's electron-phonon interaction, to investigate the carrier dynamics. It is found that PIRET deforms the wavepacket dynamics of the molecular excited state and results in ten-fold enhancement of dye absorption. MNPs augment light absorption and increase the electron density in empty molecular orbitals of the dye molecule. Consequently, this enhances the interfacial charge separation. Furthermore, we observed the interference behavior of two CSCs and gave a full-scale insight into the correlation between the constructive/destructive interference and the electronic-state properties as well as carrier-phonon interactions. This work provides a theoretical guidance to optimize DSSCs. [ABSTRACT FROM AUTHOR]

Within the well-established optical response function formalism, a new strategy with the central idea of employing the forward-backward stochastic Schrödinger equations in a segmented way to accurately obtain the two-dimensional (2D) electronic spectrum is presented in this paper. Based on the simple excitonically coupled dimer model system, the validity and efficiency of the proposed schemes are demonstrated in detail, along with the comparison against the deterministic hierarchy equations of motion and perturbative second-order time-convolutionless quantum master equations. In addition, an important insight is provided in this paper that the characteristic frequency of the overdamped environment is an extremely crucial factor to regulate the lifetimes of the oscillating signals in 2D electronic spectra and of quantum coherence features of system dynamics. It is worth noting that the proposed scheme benefiting from its stochastic nature and wavefunction framework and many other advantages of substantially reducing the numerical cost has a great potential to systematically investigate various quantum effects observed in realistic large-scale natural and artificial photosynthetic systems. [ABSTRACT FROM AUTHOR]

The thermodynamic properties of CeO2 have been reevaluated by a simple but accurate scheme. All our calculations are based on the self-consistent ab initio lattice dynamical (SCAILD) method that goes beyond the quasiharmonic approximation. Through this method, the effects of phonon-phonon interactions are included. The obtained thermodynamic properties and phonon dispersion relations are in good agreement with experimental data when considering the correction of phonon-phonon interaction. We find that the correction of phonon-phonon interaction is equally important and should not be neglected. At last, by comparing with quasiharmonic approximation, the present scheme based on SCAILD method is probably more suitable for high temperature systems. [ABSTRACT FROM AUTHOR]

Thermal rate constants for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The results reveal that the quantum effect is remarkable for the reaction at both low and high temperatures, and the obtained rates are in good agreement with experimental measurements at high temperatures. Compared to the harmonic approximation, the torsional anharmonic effect of the internal rotation has a little influence on the rates at low temperatures, however, it enhances the rate by about 20% at 1000 K. In addition, the free energy barriers for the isotopic reactions and the temperature dependence of kinetic isotope effects are also investigated. Generally speaking, for the title reaction, the replacement of OH with OD will reduce the free energy barrier, while substituting D for H (connected to C) will increase the free energy barrier. [ABSTRACT FROM AUTHOR]

A time-dependent wavepacket diffusion method is proposed to deal with charge transport in organic crystals. The electron-phonon interactions in both site energies and electronic couplings are incorporated by the time-dependent fluctuations which are generated from the corresponding spectral density functions. The numerical demonstrations reveal that the present approach predicts the consistent charge carrier dynamics with the rigorous quantum approaches. In addition, the diffusion coefficients obtained from the Marcus formula are well reproduced at the weak electronic coupling and high temperature limits. It is also found that the charge mobility feature of the crossover from the band-like to the hopping-type cannot be predicted from the fluctuations induced by the linear electron-phonon interactions with an Ohmic spectral density; however, it indeed appears as the electronic coupling fluctuation exponentially depends on the nuclear coordinates. Finally, it should be noted that although the present approach neglects the imaginary fluctuation, it essentially incorporates the coherent motion of the charge carrier and quantum effect of the phonon motion with a broad regime of the fluctuations for symmetric systems. Besides, the approach can easily be applied to systems having thousands of sites, which allows one to investigate charge transport in nanoscale organic crystals. [ABSTRACT FROM AUTHOR]

A method in time domain is proposed to investigate resonance Raman spectra of absorbed molecules on semiconductor surfaces. The charge transfer at the molecule-surface interface is incorporated with the use of an Anderson-Newns type Hamiltonian, where the surface continuum state is dealt with an expansion of Legendre polynomials for fast numerical convergence. From a model test, it is found that the intensities of Raman modes in the sole molecule generally decrease as the molecule-surface interaction is switched on, except that the energy gaps between the molecular excited state and the bottom of the band are at special values. New Raman peaks which are not observed in the sole molecule, however, appear and are greatly enhanced. The enhancement depends on the electronic coupling and the energy gap. It is also highly sensitive to the mode-specific reorganization energy in the charge transfer state, and a thousand times enhancement can be obtained at a certain reorganization energy. The corresponding electron dynamics is revealed by the population decay from the absorbed molecule. [ABSTRACT FROM AUTHOR]

Low-lying singlet states and photophysical deactivation pathways of the electronically decoupled 2-(4-cyanophenyl)-N,N-dimethylaminoethane (PCN2NM) have been investigated by the density functional theory and CASSCF/CASPT2 approaches. PCN2NM in the ground state has two dominant configurations of the alkyl-twisted and alky-stretched structures with an interconversion barrier of 2.5 kcal/mol. The predicted vibrationally resolved weak absorption and fluorescence emission of 1(S1-Lb) exhibits clearly well-resolved vibronic features, whereas 1(S1-CT) state corresponding to the redshifted fluorescence has no fine structure. Due to the presence of low-energy 1(S1/S0)CI, radiationless decay of the excited PCN2NM to the ground state is facile, once the excess energy beyond the barrier is available. Present results show reasonable agreement with experimental observations available and provide a basis for understanding of the dual fluorescence of the electronically decoupled species. [ABSTRACT FROM AUTHOR]

We consider a problem of calculating both thermal and microcanonical rate constants for nonadiabatic chemical reactions. Instead of using the conventional transition state theory, we use a generalized seam surface and introduce a concept of a coordinate dependent effective nonadiabatic transition probability based on the Zhu–Nakamura theory which can treat the nonadiabatic tunneling properly. The present approach can be combined with Monte Carlo method so as to be applicable to chemical reactions in complicated systems. The method is demonstrated to work well in wide energy and temperature range. Numerical tests also show that it is very essential for accurate evaluation of the thermal rate constant to use the generalized seam surface and take into account the nonadiabatic tunneling effect.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A quantum mechanical theory for chemical reaction rates is presented which is modeled after the [semiclassical (SC)] instanton approximation. It incorporates the desirable aspects of the instanton picture, which involves only properties of the (SC approximation to the) Boltzmann operator, but corrects its quantitative deficiencies by replacing the SC approximation for the Boltzmann operator by the quantum Boltzmann operator, exp(-βĤ). Since a calculation of the quantum Boltzmann operator is feasible for quite complex molecular systems (by Monte Carlo path integral methods), having an accurate rate theory that involves only the Boltzmann operator could be quite useful. The application of this quantum instanton approximation to several one- and two-dimensional model problems illustrates its potential; e.g., it is able to describe thermal rate constants accurately (∼10- 20% error) from high to low temperatures deep in the tunneling regime, and applies equally well to asymmetric and symmetric potentials. [ABSTRACT FROM AUTHOR]

The origin of quantum interference characteristic of bound nonlinear systems is investigated within the Bohmian formulation of time-dependent quantum mechanics. By contrast to time-dependent semiclassical theory, whereby interference is a consequence of phase mismatch between distinct classical trajectories, the Bohmian, fully quantum mechanical expression for expectation values has a quasiclassical appearance that does not involve phase factors or cross terms. Numerical calculations reveal that quantum interference in the Bohmian formulation manifests itself directly as sharp spatial/temporal variations of the density surrounding kinky trajectories. These effects are most dramatic in regions where the underlying classical motion exhibits focal points or caustics, and crossing of the Bohmian trajectories is prevented through extremely strong and rapidly varying quantum mechanical forces. These features of Bohmian dynamics, which constitute the hallmark of quantum interference and are ubiquitous in bound nonlinear systems, represent a major source of instability, making the integration of the Bohmian equations extremely demanding in such situations. [ABSTRACT FROM AUTHOR]

The thermal rate constant for a chemical reaction, k(T), can be expressed as the long time limit of the flux-side correlation C[sub fs](t)=tr[e[sup -βĤ/2]&Fcirc;e[sup -βĤ/2]e[sup iĤ/2]e[sup iĤt/h]ĥe[sup -iĤt/h]].. Previous work has focused on semiclassical (SC) approximations [implemented via an initial value representation (IVR)] for the time evolution operators exp(±iĤt/h) in the correlation function, and this paper shows how an SC-IVR can also be used to approximate the Boltzmann operators exp(-βĤ/2). Test calculations show that over a wide temperature range little error is introduced in the rate constant by this SC approximation for the Boltzmann operator. [ABSTRACT FROM AUTHOR]

A new non-Markovian stochastic Schrödinger equation at finite temperatures is presented to correctly describe charge carrier dynamics in organic molecular crystals. The electron-phonon interactions in both site energies and electronic couplings are incorporated by the time-dependent complex-valued random fluctuations which are generated from corresponding spectral density functions. The approach is thus easily extended to investigate coherent-to-hopping charge transfer in systems with thousands of molecular sites. The capability of present approach is demonstrated by numerical simulations of carrier dynamics in the spin-boson model and a realistic Fenna-Matthews-Olson complex. The results manifest that the non-Markovian effect and complex-valued random forces are essential to guarantee the detailed balance. In an application to a long-chain donor-acceptor system, it is also interesting to find a property of coherent-to-hopping charge transfer from temperature dependence of diffusion coefficients. [ABSTRACT FROM AUTHOR]

A generalized quantum Fokker-Planck theory is proposed to treat the correlated dynamics of coherent driving and Markovian dissipation. The resulting formulation is applicable to arbitrary external time-dependent driving fields and satisfies the detailed balance condition at arbitrary temperatures. Analyzed are also the formal relations among the Caldeira-Leggett quantum Fokker-Planck equation, the Bloch-Redfield theory, and the present formulation. The approach is numerically implemented to study the intramolecular hydrogen transfer reaction dynamics in a one-dimensional model system. Different forms of external pulsed driving fields are exploited and their ability to compete with concurring relaxation processes is investigated. Energy relaxation and pure dephasing are shown to have rather different influences on the reaction yield. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The competition between laser selective dissociation of the axial Co-CO bond and intramolecular energy redistribution in HCo(CO)[sub 4] is investigated. Our approach is based on an ab initio calculation of the Cartesian reaction surface Hamiltonian along the Co-CO bond distance using density functional theory. The substrate degrees of freedom are treated within the harmonic approximation. We find only two modes which are strongly coupled to the dissociation reaction, one which can be approximately described as an H-Co stretching vibration while the second one is an umbrella type vibration of the equatorial carbonyls. The region of validity for harmonic motion of the substrate normal modes is explored. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The vibrationally resolved spectral method and quantum chemical calculations are employed to reveal the structural and spectral properties of Coumarin 343 (C343), an ideal candidate for organic dye photosensitizers, in vacuum and solution. The results manifest that the ground-state energies are dominantly determined by different placements of hydrogen atom in carboxylic group of C343 conformations. Compared to those in vacuum, the electronic absorption spectra in methanol solvent show a hyperchromic property together with the redshift and blueshift for the neutral C343 isomers and their deprotonated anions, respectively. From the absorption, emission, and resonance Raman spectra, it is found that the maximal absorption and emission come from low-frequency modes whereas the high-frequency modes have high Raman activities. The detailed spectra are further analyzed for the identification of the conformers and understanding the potential charge transfer mechanism in their photovoltaic applications. [ABSTRACT FROM AUTHOR]

The vibrationally resolved absorption spectra of zinc phthalocyanine (ZnPc) aggregates (up to 70 monomers) are explored using the non-Markovian stochastic Schrödinger equation. Various types of local excitations, charge-transfer (CT) excitations, and exciton–phonon couplings are explicitly included in a comprehensive model Hamiltonian, which is parameterized by first-principles calculations. The absorption spectral simulations clarify that the two absorption bands in the Q-band region observed in experiments can be assigned to the contribution from the CT-mediated interactions, rather than the mixtures of different-type aggregates, as prevailingly assumed. Furthermore, the relative intensities of the two bands are found to be closely related to the intermolecular distance and molecular number in a ZnPc aggregate. From the investigation of the decoherence process after optical excitation, it is found that CT states can induce coherence regeneration as the time scale of charge separation is much faster than that of the vibration-induced decoherence. However, they would instead boost the decoherence process as the two time scales become comparable. The two different effects of CT states may suggest a novel way to regulate the decoherence process in excitation energy relaxation. [ABSTRACT FROM AUTHOR]

A non-Markovian stochastic Schrödinger equation developed in our former work [Y. Ke and Y. Zhao, J. Chem. Phys. 147, 184103 (2017)] is extended to the reciprocal (k-) space to calculate the carrier dynamics in organic semiconductors with both local and nonlocal carrier-phonon interactions taken into account. The validity of this approach is examined by comparing with numerically exact benchmark results. As an application, the carrier mobilities are calculated within a one-dimensional periodic lattice model. The results reveal an inversion in the magnitude of the mobility as the nonlocal carrier-phonon interaction varies from weak to strong strengths, indicating a transition of the transport mechanism. This is also demonstrated by a variation in the temperature dependence of the mobility. In addition, a transient localization diffusive behavior caused by intramolecular vibrations is also found. [ABSTRACT FROM AUTHOR]

Semiclassical Marcus electron transfer theory is often employed to investigate the charge transport properties of organic semiconductors. However, quite often the electronic couplings vary several orders of magnitude in organic crystals, which goes beyond the application scope of semiclassical Marcus theory with the first-order perturbative nature. In this work, we employ a generalized nonadiabatic transition state theory (GNTST) [Zhao et al., J. Phys. Chem. A 110, 8204 (2004)], which can evaluate the charge transfer rates from weak to strong couplings, to study charge transport properties in prototypical organic semiconductors: quaterthiophene and sexithiophene single crystals. By comparing with GNTST results, we find that the semiclassical Marcus theory is valid for the case of the coupling <10 meV for quaterthiophene and <5 meV for sexithiophene. It is shown that the present approach can be applied to design organic semiconductors with general electronic coupling terms. Taking oligothiophenes as examples, we find that our GNTST-calculated hole mobility is about three times as large as that from the semiclassical Marcus theory. The difference arises from the quantum nuclear tunneling and the nonperturbative effects. [ABSTRACT FROM AUTHOR]