Exploring the State Space Structure of Multiple Spins via Modular Tensor Diagram Approach: Going beyond the Exciton Pair State.

Fully understanding of multistate quantum systems could become formidable if not impossible as the system dimensionality increases. One ideal strategy to comprehend complex systems is to transform the system representation into a more structural one so that major characteristics, connections, and even underlying mechanisms can stand out from the huge unstructured information, e.g., the construction of spin eigenfunctions for a system of multiple spins through the diagonalization of the system Hamiltonian matrix. Here, instead of direct matrix diagonalization, the recently developed modular tensor diagram approach is applied to reorganize the state space structure of multispin systems, extending previous investigations on exciton pair states to exciton trimer states. This implementation demonstrates that the proposed approach not only provides a systematical way to transform the high dimensional multistate system into a well organized structure based on basic (exciton) modules but also paves the way to further analysis on potential applications. For example, the analysis on the state space of the exciton trimer system suggests a possible scheme to improve the laser performance via single fission involving multiexcitations and/or multiple fission steps.

Topology of quantum coherence networks in singlet fission: mapping exciton states into real space and the dislocation induced three dimensional manifolds.

An understanding of the global structure of quantum coherence networks in coupled multistate systems is of great importance for the development of emerging quantum technologies such as quantum control and quantum materials design. Here, we study the topology of a quantum coherence network of a typical singlet exciton fission system by mapping the exciton states into crystal structures in real space. The defects in crystals could lead to changes in the topological structures, and also fission dynamics. In particular, we demonstrate that the dislocation induced three dimensional manifold, which differs from its lower dimensional counterparts globally, could generate exotic global structures, such as chiral spirals, and modulate singlet fission substantially. The findings may shed light on the new possibilities of engineering effective structures for fission materials.

Modular Tensor Diagram Approach for the Construction of Spin Eigenfunctions: The Case Study of Exciton Pair States.

Mapping out the high-dimensional state space would be valuable for better understanding the multistate quantum systems. Here, we demonstrate that high-dimensional spin state space can be mapped onto a tensor diagram in full dimension or self-similarly onto the reduced base state space. Based on the tensor diagram, a modular approach is proposed to construct spin eigenfunctions taking the basis of the lower-dimensional space as modules. The implementation of the approach on exciton pair states results in 16 spin eigenstates including 2 singlet states, 3 triplet states, and 1 quintet state with proper symmetry, in contrast to the ones generated using the conventional branching diagram method. The corresponding state energies obtained show the order of spin eigenstates reverses with respect to spin multiplicity. Interestingly, the state space can be decomposed into three subspaces corresponding to the singlet-singlet pair, singlet-triplet pair, and triplet-triplet pair, resulting in a modular structure that is invariant as intermolecular interactions diminish. The proposed approach offers a new perspective on the state space structure of multiple spin states, featuring a hierarchical symmetry, which could be extended to general high-dimensional quantum multistate systems.

Topology of quantum coherence in singlet fission: Mapping out spin micro-states in quasi-classical nonadiabatic simulations.

Quantum coherence plays an important role in exciton dynamics such as singlet fission, which may be determined by molecular physical properties, including energy levels, electronic couplings, and electron-phonon couplings, and by geometric properties, including packing configuration and exciton delocalization. However, the global picture of quantum coherence in high-dimensional multistate systems is still blurred. Here, we perform nonadiabatic molecular dynamics simulation for singlet fission in tetracene clusters and demonstrate that the topology of quantum coherence in terms of the global structure of the coupled multistate system may significantly modulate fission dynamics. In particular, quantum coherence in the spin-specified models could be protected by its topological structure from external perturbations. Our work suggests that the topology of quantum coherence is indispensable in the understanding and control of quantum dynamics, which may find potential implementations to singlet fission and quantum computation.

Electrolyte Solvation Manipulation Enables Unprecedented Room-Temperature Calcium-Metal Batteries.

Calcium-metal batteries (CMBs) provide a promising option for high-energy and cost-effective energy-storage technology beyond the current state-of-the-art lithium-ion batteries. Nevertheless, the development of room-temperature CMBs is significantly impeded by the poor reversibility and short lifespan of the calcium-metal anode. A solvation manipulation strategy is reported to improve the plating/stripping reversibility of calcium-metal anodes by enhancing the desolvation kinetics of calcium ions in the electrolyte. The introduction of lithium salt changes the electrolyte structure considerably by reducing coordination number of calcium ions in the first solvation shell. As a result, an unprecedented Coulombic efficiency of up to 99.1 % is achieved for galvanostatic plating/stripping of the calcium-metal anode, accompanied by a very stable long-term cycling performance over 200 cycles at room temperature. This work may open up new opportunities for development of practical CMBs.

Nonadiabatic Dynamics of Hydrogen Diffusion on Cu(001): Classical Mapping Model with Multistate Projection Window in Real Space.

Diffusion of atomic hydrogen on metallic surfaces is a longstanding research topic of both fundamental and practical interests. However, full understanding of the microscopic mechanisms and development of effective strategy for surface dynamics control at the molecular level remain elusive. In this paper, we propose a new nonadiabatic multistate model for surface diffusion based on a real space decomposition scheme by generalizing the classical mapping theory of Meyer and Miller. The model suggests a general multistate perspective on real-time surface dynamics by mapping it into spatially disjointed windowing functions, which feature the explicit nonadiabatic controllability. Within this framework, the first nonadiabatic molecular dynamics simulation is performed for atomic hydrogen diffusion on the Cu(001) surface, and the nonequilibrium effect of lattice distortion is studied.

Effects of FOXJ2 on TGF-ß1-induced epithelial-mesenchymal transition through Notch signaling pathway in non-small lung cancer.

As one member of Forkhead box transcription factors, Forkhead box J2 (FOXJ2) has been found to be involved in epithelial-mesenchymal transition (EMT) process. However, the role and mechanism of FOXJ2 in non-small cell lung cancer (NSCLC) and EMT regulation have not been fully revealed. In this paper, it was revealed that the expression of FOXJ2 was lower in NSCLC samples compared with matched peritumoral lung tissue. We demonstrated that FOXJ2 expression was down-regulated by transforming growth factor-ß1 (TGF-ß1) treated, and overexpression of FOXJ2 inhibited TGF-ß1-induced EMT. Mechanistically, knocking out the expression of FOXJ2 promoted EMT by increasing the expression of Notch1 and NICD. This study implicates the potential value of FOXJ2 as a molecular marker for NSCLC.

Mapping State Space to Quasiclassical Trajectory Dynamics in Coherence-Controlled Nonadiabatic Simulations for Condensed Phase Problems.

Recently a coherence controlled (CC) approach to nonadiabatic dynamics was proposed by one of the authors based on the mapping between the decomposed classical state space and different types of nuclear dynamics. Here we elaborate the state-space decomposition scheme and the corresponding state-space-to-dynamics mapping of the CC approach in a general high-dimensional framework. In the CC formalism, dynamical properties such as the full electronic matrix can be evaluated by means of the ensemble of trajectories in the active state space, which consists of single-state domains and coherence domains. The feasibility of the state space decomposition and related mappings and the performance of the CC approach are demonstrated by the implementation to benchmark problems of nonadiabatic molecular dynamics in condensed phase including the spin-boson model and the excitation energy transfer problem in photosynthesis. The results obtained from the CC approach are in reasonably good agreement with exact or benchmark calculations, and it is also shown that the CC approach satisfies the detailed balance approximately and is capable of efficiently describing condensed phase nonadiabatic molecular dynamics at reasonable accuracy.

Multi-state trajectory approach to non-adiabatic dynamics: General formalism and the active state trajectory approximation.

A general theoretical framework is derived for the recently developed multi-state trajectory (MST) approach from the time dependent Schrödinger equation, resulting in equations of motion for coupled nuclear-electronic dynamics equivalent to Hamilton dynamics or Heisenberg equation based on a new multistate Meyer-Miller (MM) model. The derived MST formalism incorporates both diabatic and adiabatic representations as limiting cases and reduces to Ehrenfest or Born-Oppenheimer dynamics in the mean-field or the single-state limits, respectively. In the general multistate formalism, nuclear dynamics is represented in terms of a set of individual state-specific trajectories, while in the active state trajectory (AST) approximation, only one single nuclear trajectory on the active state is propagated with its augmented images running on all other states. The AST approximation combines the advantages of consistent nuclear-coupled electronic dynamics in the MM model and the single nuclear trajectory in the trajectory surface hopping (TSH) treatment and therefore may provide a potential alternative to both Ehrenfest and TSH methods. The resulting algorithm features in a consistent description of coupled electronic-nuclear dynamics and excellent numerical stability. The implementation of the MST approach to several benchmark systems involving multiple nonadiabatic transitions and conical intersection shows reasonably good agreement with exact quantum calculations, and the results in both representations are similar in accuracy. The AST treatment also reproduces the exact results reasonably, sometimes even quantitatively well, with a better performance in the adiabatic representation.

A multi-state trajectory method for non-adiabatic dynamics simulations.

A multi-state trajectory approach is proposed to describe nuclear-electron coupled dynamics in nonadiabatic simulations. In this approach, each electronic state is associated with an individual trajectory, among which electronic transition occurs. The set of these individual trajectories constitutes a multi-state trajectory, and nuclear dynamics is described by one of these individual trajectories as the system is on the corresponding state. The total nuclear-electron coupled dynamics is obtained from the ensemble average of the multi-state trajectories. A variety of benchmark systems such as the spin-boson system have been tested and the results generated using the quasi-classical version of the method show reasonably good agreement with the exact quantum calculations. Featured in a clear multi-state picture, high efficiency, and excellent numerical stability, the proposed method may have advantages in being implemented to realistic complex molecular systems, and it could be straightforwardly applied to general nonadiabatic dynamics involving multiple states.

Methylation of OPCML promoter in ovarian cancer tissues predicts poor patient survival.

BACKGROUND: Ovarian cancer is a lethal gynecological malignancy largely due to the lack of biomarkers for early detection and treatment options. Opioid binding protein/cell adhesion molecule-like gene (OPCML) has a tumor-suppressor function in ovarian cancer, and epigenetic inactivation of OPCML induces oncogenic transformation of human ovarian surface epithelial cells. METHODS: This study investigated OPCML promoter methylation levels in ovarian cancer tissues. A total of 30 normal ovarian, 85 benign ovarian tumor, and 102 ovarian cancer tissues were subjected to quantitative methylation-specific PCR analysis of OPCML methylation. Four ovarian cancer cell lines were cultured and treated with the DNA demethylation agent 5-aza-2'-deoxycytidine (5-AZA) for restoring OPCML expression. RESULTS: The data showed that 80 of 102 (78.4%) ovarian cancer tissues and 28 of 85 (32.9%) benign ovarian tumors had a methylated OPCML gene promoter. In contrast, there was no OPCML gene promoter methylation in any of the 30 normal ovarian samples. OPCML promoter methylation was significantly associated with an older age of the patients (p=0.022), an advanced pathological stage of ovarian cancer (p=0.023), and poor overall survival of ovarian cancer patients (p<0.001). Multivariate analysis data showed that pathological stage, age, and OPCML promoter methylation were all independent factors to predict overall survival of patients. Furthermore, 5-AZA was able to restore expression of OPCML mRNA and protein in ovarian cancer cell lines. CONCLUSIONS: These data indicate that detection of OPCML gene promoter methylation could be a useful biomarker for predicting the prognosis of ovarian cancer patients and disease progression.

Detection of circulating methylated opioid binding protein/cell adhesion molecule-like gene as a biomarker for ovarian carcinoma.

BACKGROUND: Hypermethylation of the opioid binding protein/cell adhesion molecule-like (OPCML) gene is frequently observed in ovarian carcinoma. We evaluated the detection of circulating hypermethylated OPCML for detecting ovarian carcinoma and assessing its prognosis. METHODS: We studied 85 tissue samples including 45 ovarian cancer tissues and 40 normal ovarian tissues and blood samples from 45 ovarian cancer patients and 20 healthy individuals. Bisulfite sequencing and methylation-sensitive restriction enzyme-PCR (MSRE-PCR) were used to detect the frequency of OPCML hypermethylation. RESULTS: We detected that the frequency of OPCML hypermethylation for tissue and serum samples in ovarian carcinoma were 86.7% (39/45) and 80.0% (36/45), respectively, but none was detected in ovarian tissue and serum of healthy individuals. The frequency of OPCML hypermethylation in endometrioid carcinoma, serous cystadenocarcinoma, mucinous cystadenocarcinoma, clear cell carcinoma, and undifferentiated carcinoma were 80.0%, 85.5%, 50.0%, 80.0%, and 100%, respectively (p > 0.05). The frequencies of OPCML hypermethylation in patients were also different in terms of tumor differentiation degree. We detected hypermethylated OPCML in the sera of 50% of well differentiated, 62.5% of moderately differentiated, 93.1% of poorly differentiated tumors (p < 0.05). The frequency of OPCML hypermethylation at FIGO stage I was 42.9%, stage II was 66.7%, stage III was 85.7%, stage IV was 100% (p < 0.05). CONCLUSIONS: Detection OPCML methylation in the serum is useful for ovarian carcinoma diagnosis.

Silver Nanowire Aerogel Support Promotes Stable Hydrogen Evolution Reaction at High Current Density.

The stability of electrocatalysts during the hydrogen evolution reaction (HER) is vital for efficient production of hydrogen energy. Herein, we demonstrate that silver nanowire aerogel-based support (AABS) could facilitate the construction of HER catalysts with extraordinary long-term stability. A full nanostructure catalyst of nickel phosphide based formed on AABS (Ni2P-Ni5P4@AABS) was prepared to achieve an overpotential of 687 mV (without iR compensation) for HER at the current density of 1 A cm-2 in 0.5 M H2SO4. Excitingly, the stable HER performance was kept for 42 days during the long-term stability (i-t) test at high current density (0.5-1 A cm-2). The excellent HER performance of the Ni2P-Ni5P4@AABS catalyst is attributed to rapid electron transport pathways, numerous more accessible active sites, and support induced enhanced catalytic activity. The support effect was highlighted by a proposed phenomenological two-channel model for electron transport, which provides fresh insights into the design strategy for energy storage and delivery.

Electronically nonadiabatic dynamics in complex molecular systems: an efficient and accurate semiclassical solution.

Chemical reaction dynamics is always a central theme in chemistry research. In many important chemical processes, reaction dynamics is electronically nonadiabatic, i.e., dynamics involves coupled multiple electronic states. We demonstrate in this paper that a semiclassical (SC) treatment based on an initial value representation methodology and a classical mapping formalism for the electronic degrees of freedom is now able to provide a rigorous and practical solution to electronically nonadiabatic dynamics in complex molecular systems. The key component of this treatment is to incorporate a correlated importance sampling protocol in nonadiabatic SC calculations, which results in a speedup factor of 100 or more in comparison with that using the standard sampling approach. This is illustrated by application to a two-state model coupled with up to 10 nuclear bath modes for a benchmark nonadiabatic excitation energy transfer problem. This work provides great opportunities for the effectively theoretical investigations on reaction mechanisms in complex molecular systems, in which electronically nonadiabatic dynamics plays an importance role.

Communication: importance sampling including path correlation in semiclassical initial value representation calculations for time correlation functions.

Full semiclassical (SC) initial value representation (IVR) for time correlation functions involves a double phase space average over a set of two phase points, each of which evolves along a classical path. Conventionally, the two initial phase points are sampled independently for all degrees of freedom (DOF) in the Monte Carlo procedure. Here, we present an efficient importance sampling scheme by including the path correlation between the two initial phase points for the bath DOF, which greatly improves the performance of the SC-IVR calculations for large molecular systems. Satisfactory convergence in the study of quantum coherence in vibrational relaxation has been achieved for a benchmark system-bath model with up to 21 DOF.

Hydrogen-bonding and π-π interaction promoted solution-processable covalent organic frameworks.

Covalent organic frameworks show great potential in gas adsorption/separation, biomedicine, device, sensing, and printing arenas. However, covalent organic frameworks are generally not dispersible in common solvents resulting in the poor processability, which severely obstruct their application in practice. In this study, we develop a convenient top-down process for fabricating solution-processable covalent organic frameworks by introducing intermolecular hydrogen bonding and π-π interactions from ionic liquids. The bulk powders of imine-linked, azine-linked, and ß-ketoenamine linked covalent organic frameworks can be dispersed homogeneously in optimal ionic liquid 1-methyl-3-octylimidazolium bromide after heat treatment. The resulting high-concentration colloids are utilized to create the covalent organic framework inks that can be directly printed onto the surface. Molecular dynamics simulations and the quantum mechanical calculations suggest that C‒H···π and π-π interaction between ionic liquid cations and covalent organic frameworks may promote the formation of colloidal solution. These findings offer a roadmap for preparing solution-processable covalent organic frameworks, enabling their practical applications.

Time-dependent importance sampling in semiclassical initial value representation calculations for time correlation functions. II. A simplified implementation.

An efficient time-dependent (TD) Monte Carlo (MC) importance sampling method has recently been developed [G. Tao and W. H. Miller, J. Chem. Phys. 135, 024104 (2011)] for the evaluation of time correlation functions using the semiclassical (SC) initial value representation (IVR) methodology. In this TD-SC-IVR method, the MC sampling uses information from both time-evolved phase points as well as their initial values, and only the "important" trajectories are sampled frequently. Even though the TD-SC-IVR was shown in some benchmark examples to be much more efficient than the traditional time-independent sampling method (which uses only initial conditions), the calculation of the SC prefactor-which is computationally expensive, especially for large systems-is still required for accepted trajectories. In the present work, we present an approximate implementation of the TD-SC-IVR method that is completely prefactor-free; it gives the time correlation function as a classical-like magnitude function multiplied by a phase function. Application of this approach to flux-flux correlation functions (which yield reaction rate constants) for the benchmark H + H(2) system shows very good agreement with exact quantum results. Limitations of the approximate approach are also discussed.

Hydrogen-bonding and "π-π" interaction promoted solution-processable mixed matrix membranes for aromatic amines detection.

Detection of hazardous compounds can alleviate risk to human health. However, it remains a challenge to develop easy-to-use testing tools for carcinogenic aromatic amines. Herein, we presented a conjugated molecule-based aniline detector, mixed matrix membranes (MMMs), through the solution-processable strategy. The pentacene-based dispersed phase is achieved using the state-of-the-art ionic liquids (ILs) as the continuous phase, based on which MMMs are easily manufactured by a solution process. Moreover, molecular dynamics (MD) simulations and quantum mechanical calculations suggested that hydrogen bonding and π-π interaction between ILs cations and pentacene could promote the dissolution. These prepared MMMs can offer easy-operation and on-site detection of carcinogenic primary aromatic amines with eye-readable fluorescence signal. This work provides a paradigm for the design of a portable testing device for various hazardous compounds.

Time-dependent importance sampling in semiclassical initial value representation calculations for time correlation functions.

An efficient time-dependent importance sampling method is developed for the Monte Carlo calculation of time correlation functions via the initial value representation (IVR) of semiclassical (SC) theory. A prefactor-free time-dependent sampling function weights the importance of a trajectory based on the magnitude of its contribution to the time correlation function, and global trial moves are used to facilitate the efficient sampling the phase space of initial conditions. The method can be generally applied to sampling rare events efficiently while avoiding being trapped in a local region of the phase space. Results presented in the paper for two system-bath models demonstrate the efficiency of this new importance sampling method for full SC-IVR calculations.

Renormalization of the frozen Gaussian approximation to the quantum propagator.

The frozen Gaussian approximation to the quantum propagator may be a viable method for obtaining "on the fly" quantum dynamical information on systems with many degrees of freedom. However, it has two severe limitations, it rapidly loses normalization and one needs to know the Gaussian averaged potential, hence it is not a purely local theory in the force field. These limitations are in principle remedied by using the Herman-Kluk (HK) form for the semiclassical propagator. The HK propagator approximately conserves unitarity for relatively long times and depends only locally on the bare potential and its second derivatives. However, the HK propagator involves a much more expensive computation due to the need for evaluating the monodromy matrix elements. In this paper, we (a) derive a new formula for the normalization integral based on a prefactor free HK propagator which is amenable to "on the fly" computations; (b) show that a frozen Gaussian version of the normalization integral is not readily computable "on the fly"; (c) provide a new insight into how the HK prefactor leads to approximate unitarity; and (d) how one may construct a prefactor free approximation which combines the advantages of the frozen Gaussian and the HK propagators. The theoretical developments are backed by numerical examples on a Morse oscillator and a quartic double well potential.