Journal of Chemical Physics最新文献

We explore the role of molecular vibrations in the chirality-induced spin selectivity (CISS) effect in the context of charge transport through a molecular nanojunction. We employ a mixed quantum-classical approach that combines Ehrenfest dynamics for molecular vibrations with the hierarchical equations of motion method for the electronic degrees of freedom. This approach treats the molecular vibrations in a nonequilibrium manner, which is crucial for the dynamics of molecular nanojunctions. To explore the effect of vibrational dynamics on spin selectivity, we also introduce a new figure of merit, the displacement polarization, which quantifies the difference in vibrational displacements for opposing lead magnetizations. We analyze the dynamics of single trajectories, investigating how the spin selectivity depends on voltage and electronic-vibrational coupling. Furthermore, we investigate the dynamics and temperature dependence of ensemble-averaged observables. We demonstrate that spin selectivity is correlated in time with the vibrational polarization, indicating that the dynamics of molecular vibrations is the driving force of CISS in this model within the Ehrenfest approach.

Complex organic molecules are widespread in different areas of the interstellar medium, including cold areas, such as molecular clouds, where chemical reactions occur in ice. Among the observed molecules are oxygen-bearing organic molecules, which are of high interest given their significant role in astrobiology. Despite the observed rich chemistry, the underlying molecular mechanisms responsible for molecular formation in such cold dilute areas are still not fully understood. In this paper, we study the unique chemistry taking place in astronomically relevant ices, where UV radiation is a central driving force for chemical reactions. Photofragmentation of ice components gives rise to highly reactive species, such as the O(1D) atom. These species provide a pathway for chemical complexity even in cold areas. Using quantum chemistry calculations, we demonstrate that O(1D) reacts barrierlessly with hydrocarbons. Moreover, photoprocessing of the reaction products (and other components of the ice), followed by radical recombination, is found to be an essential part of the overall mechanism. In ice containing O(1D) and hydrocarbons, the formation of formaldehyde in methane ice, acetaldehyde in ethane ice, and carbon monoxide in acetylene ice, and the consumption of alcohol in all systems, was predicted in agreement with experimental results.

Isonitrile-derivatized amino acids are emerging as highly effective infrared (IR) probes for investigating the structures and dynamics of hydrogen (H)-bonds. These probes enable the quantification of chemical exchange processes in solute-solvent complexes via two-dimensional IR spectroscopy and hold significant promise for site-specific dynamic studies within proteins. Despite their potential, theoretical models that elucidate the solvatochromism of isonitriles remain underdeveloped. Here, we present the development and validation of a solvatochromic charge model for isonitrile (N≡C) probes. Using density functional theory calculations, we parameterized solvatochromic charges for isonitrile and integrated them into classical molecular dynamics (MD) simulations of β-isocyanoalanine in various solvents, including water and fluorinated alcohols. The model incorporates solvent-induced frequency shifts and accurately reproduces complex experimental line shapes, including asymmetric features from non-Gaussian dynamics. The model successfully reproduced the bimodal distribution of frequency shifts corresponding to free and H-bonded species in alcohols, as well as cross-peaks due to chemical exchange. Achieving reproducibility required long MD trajectories, which were computationally demanding. To manage this, we implemented graphics processing unit acceleration, drastically reducing the computational time and enabling the efficient processing of extensive MD data. While some discrepancies in population ratios suggest the need for refined solvent force field parameters and modeling transition dipole moment variations, the developed solvatochromic model is a reliable tool for studying the solvation dynamics. The model enables more detailed investigations of ultrafast dynamics in solute-solvent complexes and represents important steps toward modeling site-specific dynamics of biomolecules with isonitrile probes.

We outline two general theoretical techniques to simulate polariton quantum dynamics and optical spectra under the collective coupling regimes described by a Holstein-Tavis-Cummings (HTC) model Hamiltonian. The first one takes advantage of sparsity of the HTC Hamiltonian, which allows one to reduce the cost of acting polariton Hamiltonian onto a state vector to the linear order of the number of states, instead of the quadratic order. The second one is applying the well-known Chebyshev series expansion approach for quantum dynamics propagation and to simulate the polariton dynamics in the HTC system; this approach allows us to use a much larger time step for propagation and only requires a few recursive operations of the polariton Hamiltonian acting on state vectors. These two theoretical approaches are general and can be applied to any trajectory-based non-adiabatic quantum dynamics methods. We apply these two techniques with our previously developed Lindblad-partially linearized density matrix approach to simulate the linear absorption spectra of the HTC model system, with both inhomogeneous site energy disorders and dipolar orientational disorders. Our numerical results agree well with the previous analytic and numerical work.

The reaction CH3NC ⇌ CH3CN, a model reaction for the study of unimolecular isomerization, is important in astronomy and atmospheric chemistry and has long been studied by numerous experiments and theories. In this work, we report the first full-dimensional accurate potential energy surface (PES) of this reaction by the permutation invariant polynomial-neural network method based on 30 974 points, whose energies are calculated at the CCSD(T)-F12a/AVTZ level. Then, ring polymer molecular dynamics is used to derive the free energy barrier of the reaction at the experimental temperature range of 472.55-532.92 K. Reaction kinetics are studied at the high-pressure limit and in the fall-off region by standard transition state theory and the master equation, respectively. The calculated temperature- and pressure-dependent rate coefficients are in good agreement with previous experimental and theoretical results. Furthermore, quasi-classical trajectory simulations are performed on this PES to study the intramolecular energy transfer dynamics at initial vibrational energies of 4.336, 5.204, and 6.505 eV.

Rigid, non-polarizable water models are very efficient from a computational point of view, and some of them have a great ability in predicting experimental properties. There is, however, little room for improvement in simulating water with this strategy, whose main shortcoming is that water molecules do not change their interaction parameters in response to the local molecular landscape. In this work, we propose a novel modeling strategy that involves using two rigid non-polarizable models as states that water molecules can adopt depending on their molecular environment. During the simulation, molecules dynamically transition from one state to another depending on a local order parameter that quantifies some local structural feature. In particular, molecules belonging to low- and high-tetrahedral order environments are represented with the TIP4P/2005 and TIP4P/Ice rigid models, respectively. In this way, the interaction between water molecules is strengthened when they acquire a tetrahedral coordination, which can be viewed as an effective way of introducing polarization effects. We call the resulting model TIP4P2005Ice and show that it outperforms either of the rigid models that build it. This multi-state strategy only slows down simulations by a factor of 1.5 compared to using a standard non-polarizable model and holds great promise for improving simulations of water and aqueous solutions.

Accurate Rayleigh and Raman scattering cross sections, tensor components, depolarization ratios, and reversal coefficients for all rovibrational transitions within the X1Σg+ ground electronic state of H2 have been calculated. Raman spectra have been generated using these data. A method for calculating Raman scattering cross sections is formulated that is valid below the ionization threshold and in the region containing resonances, which explicitly accounts for all bound and dissociative vibrational levels of the bound intermediate electronic states and approximately accounts for the ionization continuum. A representative set of cross sections is presented for incident photon energies below 15 eV and compared with existing results in the literature where possible. Convergence of our results with an increasing number of bound intermediate electronic states is demonstrated. The accuracy of the Placzek-Teller approximation is discussed. The effect of accounting for the intermediate ionization continuum is investigated. Local thermal equilibrium cross sections are calculated for Rayleigh and Raman scattering. This work represents the most accurate and complete treatment of Raman scattering for molecular hydrogen to date. A total of 9582 Rayleigh and Raman scattering cross sections have been generated and are openly available on Zenodo under an open-source Creative Commons Attribution license at https://zenodo.org/doi/10.5281/zenodo.13441471.

The intersection of quantum chemistry and quantum computing has led to significant advancements in understanding the potential of using quantum devices for the efficient calculation of molecular energies. Simultaneously, this intersection enhances the comprehension of quantum chemical properties through the use of quantum computing and quantum information tools. This paper tackles a key question in this relationship: Is the nature of the orbital-wise electron correlations in wavefunctions of realistic prototypical cases classical or quantum? We address this question with a detailed investigation of molecular wavefunctions in terms of Shannon and von Neumann entropies, common tools of classical and quantum information theory. Our analysis reveals a notable distinction between classical and quantum mutual information in molecular systems when analyzed with Hartree-Fock canonical orbitals. However, this difference decreases dramatically, by ∼100-fold, when natural orbitals are used as reference. This finding suggests that orbital correlations, when viewed through the appropriate basis, are predominantly classical. Consequently, our study underscores the importance of using natural orbitals to accurately assess molecular orbital correlations and to avoid their overestimation.

In this paper, we present a detailed investigation of the structural, magnetic, and electrical transport properties of Eu2-xCuxRu2O7 (x = 0, 0.2, 0.4) pyrochlores. X-ray diffraction measurements confirm the single-phase nature of all samples and also manifest the reduction of lattice parameters with the increase in copper doping concentration. The experimental results of the magnetic measurements indicate that an anomalous magnetic transition around 23 K arises due to the contribution of non-magnetic Eu3+ ions. The strength of this unnatural magnetic transition reduces with decreasing Eu concentration [i.e., with increasing copper doping (x)] and finally disappears for x = 0.4. Moreover, electrical transport measurements reveal a considerable decrease in resistivity for Cu doped samples compared to undoped samples, which indicates the increase in charge carrier concentration with increasing Cu content.