Journal of Chemical Physics最新文献

Light-energy conversion processes causing alternations in spin multiplicity are attracting attention, but the development of quantum sensing technology applicable to fluid environment such as inside cells has been unexploited. How to achieve efficient energy conversion with controlling spin quantum coherence in a noisy condensed system is challenging. In this study, we investigate the effect of molecular motion on electron spin polarization to control quantum information of three-spin qubits in a fluid environment by using steric effects of organic molecules at room temperature. Using time-resolved electron paramagnetic resonance to observe light-induced generation and transfer of quantum entanglement, we directly observed a photoexcited quartet state generated in a radical-chromophore coupled system and clarified details of the electron spin polarization mechanism including a decoherence effect by activation of anisotropic molecular motion by the steric effects.

Reorienting polyatomic ions such as NH4+ and NO3- exhibit weak magnetic fields because the ions at the extremities trace out current loops; if the periodic reorientations become long-range ordered (i.e., gearing of neighboring NO3-), then the magnetic susceptibility should exhibit a unique signature along the different crystallographic axes. For the case of ammonium nitrate (NH4NO3), we report the presence of two successive sharp steps in the molar magnetic susceptibility along the a- and b-axes upon crossing its order-disorder phase transition (from phase IV to phase II). We suggest that the first step pertains to the NO3- planes shifting away from facing only along the b-axis and onto the a-axis by 45°. The second step is attributed to the disordering (ungearing) of the NH4+ and NO3-. In contrast, only one step was observed in the magnetic susceptibility along the c-axis, and its large magnitude suggests that the NO3- remain weakly correlated even in phase I at 400 K. We also find evidence that the NH4+ become magnetically ordered (geared) along the c-axis only until phase V. The approach employed in this work can be extended to experimentally study the lattice dynamics of other solids possessing planar ions such as amphidynamic crystals.

Charge conductivity in conducting polymers is typically improved by increasing carrier density via chemical oxidation. However, the resulting electrostatic stabilization of the carriers by the dopant ions, combined with their nanostructural environment, are both known to crucially affect charge trapping. Although the effects of charge-ion electrostatic interactions on carrier trapping have been well-characterized using conventional infrared (IR) spectroscopy, the impacts of the polymer chain ordering and energetic environment are difficult to disentangle. In this study, we examine the limitations of conventional IR absorption spectroscopy and introduce a complementary spectroscopic approach capable of discerning polaron trapping more generally. To do so, we investigated films of poly(3-hexylthiophene-2,5-diyl) (P3HT) chemically doped using four different oxidants, of which each preferentially dopes the amorphous and crystalline (lamellar) phases to varying extents. Using this model system, we observed counterintuitive shifts in the polaron IR absorption band, indicating that IR spectroscopy is a clear reporter of trapping only when the carriers exclusively reside in the lamellar phase and in the absence of bipolarons or coupled polarons. Alternatively, we found that polaron excited state dynamics, probed using ultrafast near-infrared transient absorption spectroscopy, more clearly report on charge trapping. This study demonstrates near-infrared transient absorption spectroscopy as a complementary tool for probing charge trapping in conducting polymers when doping induces carriers in different nanostructural environments.

Single molecule experiments monitor the structural transitions of biomolecules under a constant mechanical force to study their fold-unfold transitions. The activation barrier for such transitions is obtained by inverting the observed committor, which is the probability that the molecule starting from a given extension reaches the folded state before the unfolded state. This work proposes an analytical model for committor analysis of the multi-state conformational dynamics of a DNA hairpin in a complex cellular environment, within the framework of the generalized Langevin equation using a general asymmetric bistable potential with a power-law frictional memory kernel. We obtained exact analytical expressions for the probability density function, first passage time distribution, and the committor. The results are compared with those obtained from steered molecular dynamics simulation of a three-state DNA hairpin, and earlier experimental data. We investigated the dependence of the committor and the corresponding committor-inverted profiles on the linker stiffness, barrier height, and degree of asymmetry in the bistable potential. This model successfully captures the fold-unfold dynamics, reproducing the multi-state free energy profile with asymmetric energy barriers.

The multilayer-multiconfiguration time-dependent Hartree (ML-MCTDH) method has garnered significant attention in the realm of theoretical chemistry owing to its powerful ability to perform numerically exact descriptions of multi-dimensional quantum dynamics and exhibit the remarkable performance in simulating the nonadiabatic dynamics of complex systems. Despite the availability of computational packages within the ML-MCTDH framework, executing these calculations seamlessly is not a straightforward task. Typically, substantial efforts are necessitated to configure the correct inputs for ML-MCTDH calculations, which require to correctly define several non-trivial parameters, to reasonably setup the optimal tree expansion of wavefunctions, and to properly select basis function numbers. To address these challenges, we have developed an auxiliary package named ML-MCTDH-Aid, which facilitates the setup of ML-MCTDH calculations using the Heidelberg MCTDH package in a user-friendly manner. This package is primarily tailored to handle the high-dimensional nonadiabatic dynamics governed by the Hamiltonian composed of several electronic states, several vibrational modes and their linear vibronic coupling terms. It automatically generates multiple essential input files, and all the calculations can be performed in an all-in-one black-box easy-to-use manner. To show the utility of the ML-MCTDH-Aid package, we provide a step-by-step tutorial that demonstrates running ML-MCTDH studies on three models. These examples illuminate how the utilization of the ML-MCTDH-Aid package significantly enhances the efficiency and effectiveness of ML-MCTDH calculations. This substantially boosts the accessibility of ML-MCTDH calculations in tackling the high-dimensional quantum dynamics of complex systems.

With increasing emphasis on the study of active solids, the features of these classes of nonequilibrium systems and materials beyond their mere existence shift into focus. One concept of active solids addresses them as active, self-propelled units that are elastically linked to each other. The emergence of orientationally ordered, collectively moving states in such systems has been demonstrated. We here analyze the excitability of such collectively moving elastic states. To this end, we determine corresponding fluctuation spectra. They indicate that collectively excitable modes exist in the migrating solid. Differences arise when compared to those of corresponding passive solids. We provide evidence that the modes of excitation associated with the intrinsic fluctuations are related to corresponding modes of entropy production. Overall, by our investigation, we hope to stimulate future experimental studies that focus on excitations in active solids.

The effects of damping time of electronic-vibrational resonance modes on energy transfer in photosynthetic light-harvesting systems are examined. Using the hierarchical equations of motion (HEOM) method, we simulate the linear absorption and two-dimensional electronic spectra (2DES) for a dimer model based on bottleneck sites in the light-harvesting complex of photosystem II. A site-dependent spectral density is incorporated, with only the low-energy site being coupled to the resonance mode. Similar patterns are observed in linear absorption spectra and early time 2DES for various damping times, owing to the weak coupling strength. However, notable differences emerge in the dynamics of the high-energy diagonal and cross-peaks in the 2DES. It is found that the coupling of electronic-vibrational resonance modes accelerates the energy transfer process, with rates being increased as the damping time is extended, but the impact becomes negligible when the damping time exceeds a certain threshold. To evaluate the reliability of the perturbation method, the modified Redfield (MR) method is employed to simulate 2DES under the same conditions. The results from the MR method are aligned with those obtained from the HEOM method, but the MR method predicts faster dynamics.

Amorphous oxide semiconductors have garnered significant attention in recent years for their potential in flat-panel displays and back-end-of-line-compatible monolithic 3D (M3D) integration applications. This study explores amorphous InSnZnO thin films deposited via plasma-enhanced atomic layer deposition (PEALD) and the development of high-performance PEALD ITZO thin-film transistors (TFTs) with different active layer thicknesses, fabricated under a low thermal budget of 200 °C. By optimizing the deposition process of binary oxides InOx, SnOx, and ZnOx, a shared temperature window of 170-180 °C was identified for ITZO thin-film deposition. The deposited ITZO films, irrespective of thickness, exhibit an amorphous phase. Moreover, a reduction in ITZO film thickness from 24 to 4.8 nm leads to an increase in the optical bandgap from 3.35 to 3.65 eV. The channel thickness significantly impacts the threshold voltage and carrier density of ITZO TFTs. Optimized ITZO TFTs with a 16 nm channel thickness demonstrate excellent electrical performance, including a threshold voltage of -0.58 V, a field-effect mobility of 29 cm2/V s, an on/off ratio exceeding 108, and a subthreshold swing of 74 mV/dec. Furthermore, the optimized ITZO TFT exhibits excellent stability under positive bias stress at 2 MV/cm, with a threshold voltage shift of 0.15 V after 3600 s. Consequently, ALD-based ITZO emerges as a promising channel material for future applications in transparent electronics and flat-panel displays.

Raman spectroscopy is an important tool for studying molecules, liquids and solids. While Raman spectra can be obtained theoretically from molecular dynamics (MD) simulations, this requires the calculation of electronic polarizability along the simulation trajectory. First-principles calculations of electronic polarizability are computationally expensive, motivating the development of atomistic models for the evaluation of the changes in the electronic polarizability with the changes in the atomic coordinates of the system. The bond polarizability model (BPM) is one of the oldest and simplest such atomistic models but cannot reproduce the effects of angular vibrations, leading to inaccurate modeling of Raman spectra. Here, we demonstrate that the generalization of BPM through the inclusion of terms for atom pairs that are traditionally considered to be not involved in bonding dramatically improves the accuracy of polarizability modeling and Raman spectra calculations. The generalized BPM (GBPM) reproduces the ab initio polarizability and Raman spectra for a range of tested molecules (SO2, H2S, H2O, NH3, CH4, CH3OH, and CH3CH2OH) with high accuracy and also shows significantly improved agreement with ab initio results for the more complex ferroelectric BaTiO3 systems. For liquid water, the anisotropic Raman spectrum derived from atomistic MD simulations using the GBPM evaluation of polarizability shows significantly improved agreement with the experimental spectrum compared to the spectrum derived using the BPM. Thus, the GBPM can be used for the modeling of Raman spectra using large-scale molecular dynamics and provides a good basis for the further development of atomistic polarizability models.