Coupling Theory Research Articles

Simplified Multireference Coupled-Cluster Methods: Hybrid Approaches With Averaged Coupled Pair Theories.

We define an approximation to the internally contracted multireference coupled-cluster method with single and double excitations by a hybrid approach. The rationale is to treat the external pair energy contributions by the coupled-cluster method, which provides accurate results for a large part of the correlation energy while being tractable as the involved pair cluster operators commute. For the internal and semi-internal contributions, for which the coupled-cluster part becomes involved due to non-commuting operators, a linearized approach based on the coupled-electron pair approximation (CEPA) is used. For the latter, the CEPA(0) method, the averaged coupled pair functional (ACPF), the averaged quadratic coupled-cluster (AQCC) method, and the averaged CEPA method are tested. We test the methods concerning size consistency, potential energy curves for C2, N2, CN, and O3 and for the singlet-triplet splitting of ortho-, meta-, and para-benzynes. Our results show that AQCC provides the most accurate results and stable performance. The main drawback of the method is that it shows small violations of size consistency.

Radar Scattering Analysis of Multi-Scale Complex Targets by Fast VSBR-MoM Method in Urban Scenes

An innovative and efficient hybrid technique, which combines the Method of Moments (MoM) with Volume Meshed Shooting and Bouncing Ray (VSBR), is presented to analyze the scattering of metallic–dielectric mixed multi-scale structures in urban scenes. Additionally, the technique can rapidly generate radar images at different angles, which is useful for the video remote sensing community. By dividing the mixed multi-scale targets into sub-regions, different solvers are employed to compute the scattering contributions based on their varying electrical sizes. For large-scale sub-regions, the VSBR method is employed on both the medium and metal parts, leading to a multilevel electromagnetic field including both the direct induced field and the multi-reflection field. This field contributes to the integral equation in the MoM sub-regions. Additionally, interactions from the MoM region are considered within the VSBR region, followed by a surface current integration to compute the scattered field. When addressing mixed multi-scale electromagnetic problems, this technique proves to be more efficient and easier to implement in general-purpose computer codes. Furthermore, this method is accelerated using the local coupling (LC) theory and fast multipole method (FMM). Using this fast computational method, efficient simulation results of radar images at different angles for the scenes can be obtained and the numerical results demonstrate the efficiency and accuracy of the proposed method.

Impact of Internal Solitary Wave on Acoustic Propagation Based on Coupled Normal Mode Theory

Impact of Internal Solitary Wave on Acoustic Propagation Based on Coupled Normal Mode Theory

Enhanced carrier mobility in strain-engineered PdAs2 monolayer boosted by suppressing interband scattering.

Strain engineering is an effective method to modulate the electronic properties of two-dimensional materials. In this study, we theoretically studied the carrier mobility of the PdAs2 monolayer under different biaxial tensile strains based on the state-of-the-art electron-phonon coupling theory. We observe that the carrier mobility is largely enhanced for both n-type and p-type PdAs2 monolayers. The electron mobility experiences a rapid increase under tensile strain over 2% and can reach 670 cm2 V-1 s-1 under 4% strain, which is higher than common 2D semiconductors. The rapid increase of electron mobility originates from the ordering change of the conduction bands and the suppressed interband scattering. Our study highlights the role of electron-phonon coupling in the electron transport and provides new insights into the optimization of carrier mobility.

Generalized Coupled Cluster Theory for Ground and Excited State Intersections.

Coupled cluster theory in the standard formulation is unable to correctly describe conical intersections among states of the same symmetry. This limitation has restricted the practical application of an otherwise highly accurate electronic structure model, particularly in nonadiabatic dynamics. Recently, the intersection problem among the excited states was fully characterized and resolved. However, intersections with the ground state remain an open challenge, and addressing this problem is our objective here. We present a generalized coupled cluster framework that correctly accounts for the geometric phase effect and avoids bifurcations of the solutions to the ground state equations. Several applications are presented that demonstrate the correct description of ground state conical intersections. We also propose how the framework can be used for other electronic-structure methods.

Determining Minimum Energy Conical Intersections by Enveloping the Seam: Exploring Ground and Excited State Intersections in Coupled Cluster Theory.

Minimum energy conical intersections can be used to rationalize photochemical processes. In this Letter, we examine an algorithm to locate these structures that does not require the evaluation of nonadiabatic coupling vectors, showing that it minimizes the energy on hypersurfaces that envelop the intersection seam. By constraining the states to be separated by a small non-zero energy difference, the algorithm ensures that numerical artifacts and convergence problems of coupled cluster theory at conical intersections are not encountered during the optimization. In this way, we demonstrate for various systems that geometries at minimum energy conical intersections with the ground state are well described by the coupled cluster singles and doubles model, suggesting that coupled cluster theory may, in some cases, provide a good description of relaxation to the ground state in nonadiabatic dynamics simulations.

Time‐Dependent Vibrational Coupled Cluster Theory With Static and Dynamic Basis Functions

ABSTRACTIn recent decades, coupled cluster theory has proven valuable in accurately describing correlation in many‐body systems, particularly in time‐independent computations of molecular electronic structure and vibrations. This review describes recent advancements in using coupled cluster parameterizations for time‐dependent wave functions for the efficient computation of the quantum dynamics associated with the motion of nuclei. It covers time‐dependent vibrational coupled cluster (TDVCC) and time‐dependent modal vibrational coupled cluster (TDMVCC), which employ static and adaptive basis sets, respectively. We discuss the theoretical foundation, including many‐mode second quantization, bivariational principles, and various parameterizations of time‐dependent bases. Additionally, we highlight key features that make TDMVCC promising for future quantum dynamical simulations. These features include fast configuration‐space convergence, the use of a compact adaptive basis set, and the possibility of efficient implementations with a computational cost that scales only polynomially with system size.

Research on the influence of curtain grouting parameters on the stability of tunnel surrounding rock and lining structure under the action of local high water pressure

Choosing the reasonable and economical grouting parameters is crucial for controlling the seepage field of surrounding rock and tunnel stability. This paper adopted the fluid–solid coupling theory based on FLAC3D to establish numerous simulations on the stability of surrounding rock and lining structure in karst tunnels under the different grouting conditions. The influences of grouting layer thicknesses and their permeability coefficients on the mechanical behaviors of lining structure, seepage, and stress properties of surrounding rock were investigated. The results show that with the increase of grouting thickness and its ratio of permeability, the maximum flow velocity and flow rate per liner meter in surrounding rock, the bending moments and axial forces, and the horizontal and vertical displacements of the lining structure all exponentially decrease, but safety factors at different positions of the lining structure first rapidly and then slowly increase. The changes in safety factor and uplift displacement at the inverted arch are more significant, and the minimum safety factor occurs at the left arch foot. As the grouting thickness and its ratio of permeability increase, the plastic zone range in surrounding rock decreases and expands, respectively. Through considering the improvement effect and economy of grouting comprehensively, choosing a grouting layer thickness of 7–9 m and a ratio of permeability of 20–50 is an ideal configuration parameter to ensure the stability and safety of karst tunnels under the conditions of this paper. The research results could provide references for choosing the reasonable grouting parameters in karst tunnels.

Attribution Identification of Runoff Changes Based on the Budyko Elasticity Coefficient Method: A Case Study of the Middle and Upper Reaches of the Jinghe River in the Yellow River Basin

The impacts of climate change and human activities on water resources are a complex and integrated process and a key factor for effective water resource management in semi-arid regions, especially in relation to the Jinghe River basin (JRB), a major tributary of the Yellow River basin. The Sen’s slope estimator and the Mann–Kendall test (M–K test) are implemented to examine the spatial and temporal trends of the hydrological factors, while the elasticity coefficient method based on Budyko’s theory of hydrothermal coupling is employed to quantify the degree of runoff response to the various influencing factors, from 1971 to 2020. The results reveal that the runoff at Pingliang (PL), Jingchuan (JC), and Yangjiaping (YJP) hydrological stations shows an obvious and gradual decreasing trend during the study period, with a sudden change in about 1986, while precipitation shows a fluctuating and increasing trend alongside a potential evapotranspiration-induced fluctuating and decreasing trend. Compared to the previous period, a change of −29%, in relative terms, in the runoff at the YJP hydrological station is observed. The interaction of human activities and climate change in the watershed contributes to the sharp decrease in runoff, with precipitation, potential evapotranspiration, and human activities accounting for −14.3%, −15.1%, and 70.6% of the causes of the change in runoff, respectively. Human activities (e.g., construction of water conservancy projects), precipitation, and potential evapotranspiration are the main factors contributing to the change in runoff.

High-performance dual-core photonic crystal fiber polarization beam splitter based on gold-titania composite film coating

Abstract A novel gold-titania composite film-coated dual-core photonic crystal fiber polarization beam splitter (GT-DC-PCF PBS) is proposed for the first time. The titania film and gold film are sequentially deposited on the inner wall of the central air hole to improve the polarization splitting performance and enhance the adsorption strength between the gold film and the optical fiber. Based on the mode coupling theory and surface plasmon resonance effect, the transmission characteristics of x-polarization (X-pol) and y-polarization (Y-pol) odd and even modes in the near-infrared band are analyzed by finite element method. Meanwhile, the variation of coupling length and coupling length ratio for X-pol and Y-pol light under different PCF structural parameters at the wavelength of 1550 nm are also studied to optimize the performance of PBS. The results show that at the 1550 nm communication window, the extinction ratio of the PBS is up to −175.82 dB for the polarization splitting length of 2.76 mm, with an operating bandwidth of 179 nm and a maximum insertion loss of 0.23 dB. This paper aims to propose a novel design method to improve the performance of DC-PCF PBS, which has profound guiding significance for the development of high-performance PBS.

Memory effect analysis of magneto-thermoelastic response of viscoelastic rotating nanobeams based on nonlocal and modified coupled stress elasticity theories

Memory effect analysis of magneto-thermoelastic response of viscoelastic rotating nanobeams based on nonlocal and modified coupled stress elasticity theories

Unveiling the mechanism of dynamic transverse mode instability mitigation through static mode degradation: a study in the two-mode fiber lasers.

Dynamic transverse mode instability (TMI) has become one of the primary limitations for power scaling of high-power fiber lasers. Experimental evidence has shown that static mode degradation can suppress the dynamic TMI effect. This study reveals the physical mechanisms behind the mitigation of dynamic TMI in two-mode fiber lasers through static mode degradation. Using a dynamic TMI model based on the two-beam coupling theory, we differentiate the impacts of relative intensity noise and the proportion of higher-order mode in the seed on TMI. Static mode degradation modifies the transverse gain distribution, thereby affecting the overlap between the thermally induced refractive index grating and the interference light field, which inhibits dynamic mode coupling. Our findings indicate that the effectiveness of this suppression is significantly influenced by the gain saturation. By enhancing gain saturation through strategies such as optimizing the pump injection direction, adjusting the pump wavelength, and reducing the core-to-cladding ratio, the suppression of TMI can be maximized, which is essential for advancing the performance and stability of these laser systems.

Multi-Field Coupling Models of Coal and Gas and Their Engineering Applications to CBM in Deep Seams: A Review

In the process of deep coal seam mining, the problem of coal–gas compound disasters is increasingly prominent, with the safe and efficient extraction of gas serving as the key to disaster reduction. A deep coal seam gas extraction project is a complex coupled system involving multiple physical fields, such as stress fields, gas flow fields, and energy. Constructing a systematic theoretical framework of multiphysics field coupling is crucial for improving the safety and efficiency of gas extraction. This paper examines all existing multiphysics field coupling theories. It then suggests a theoretical modeling framework that is based on three important scientific issues: the coal deformation law, the gas flow law, and the coal porosity and permeability spatiotemporal distribution law. We further analyze the application and development of the model in typical coal seam gas extraction engineering on this basis. Finally, this paper points out the shortcomings of the current research and looks forward to the future research directions for the coupled coal and gas multiphysics field model, aiming to provide a theoretical basis and guidance for the model’s construction and application in gas extraction engineering.

Exploring Similarities and Differences in Water Level Response to Earthquakes in Two Neighboring Wells Using Numerical Simulation

The seismic effect of well water level is complex and variable, and even if both wells are located in an area with similar tectonic and hydrogeological conditions, they exhibit slightly varying response characteristics to the same earthquake. Wells BB and RC, located about 100 km apart in the southwest of the Huayingshan fault zone in the Sichuan and Chongqing regions, exhibited obvious similarities and differences in their co-seismically response and sustained recovery characteristics during the Wenchuan Ms8.0 earthquake. Based on the dislocation theory and fluid–solid coupling theory, this study developed the seismic stress–strain model and the response model of pore pressure to seismic stress using Coulomb 3.3 and COMSOL 6.3, respectively. Simulation findings indicate that both BB and RC are located in the expansion zone, where their water levels show a co-seismic step-down. The amplitudes of BB and RC water levels are 83 cm and 81 cm, which are approximately 10 cm smaller than the actual values. The recovery times are 60 d for BB and 3 h for RC, closely resembling the actual values. Furthermore, the numerical results from different scenarios show that the recovery time of pore pressure is reduced by several times when the permeability of the confining layer overlying the observed aquifer increases by one order of magnitude or the thickness decreases, and this change is more sensitive to the permeability. It is clear that the confining condition has an important impact in the response time of sustained changes in well water levels, which may also help to explain the variations in the characteristics of sustained changes in wells BB and RC.

Analytical study on the flexural wave band gaps of arbitrary periodic stiffened plates by using beam-plate coupling theory

In this paper, the flexural wave band gap characteristics of periodic stiffened plates are studied by using beam-plate coupling theory. A theoretical model of arbitrary periodic stiffened plate is established considering the coupling effect of Timoshenko beam and Kirchhoff plate. The flexural wave band structures of periodic stiffened plate are calculated by using plane wave expansion method and Bloch theorem. Numerical calculation and experimental tests were conducted to verify the proposed theoretical model. In addition, the parametric studies were performed to examine the effects of geometric parameters on both bandgap and vibration reduction characteristics of periodic stiffened plate. Results show that periodic stiffened plate can yield significant flexural wave band gaps and vibration isolation performance in a specific frequency range, which shows a good agreement with numerical simulation and experimental results. The geometrical parameters of stiffened plates have a significant influence on adjusting low-frequency flexural wave band gaps. These research findings offer a new technical approach for low frequency vibration and sound optimization of stiffened structures.

A review of hydro-turbine unit rotor system dynamic behavior: Multi-field coupling of a three-dimensional model

The dynamic behavior of hydro-turbine rotor system is a complex multi-field and nonlinear problem, which has been studied by many researchers. The analysis of the rotor system dynamic characteristics is usually carried out based on the behavior analysis of bearings, hydraulics, electromagnetics, etc., while the thermo-elasto-hydrodynamic characteristics of bearings are extremely important to numerical accuracy. Therefore, this paper first summarizes the research progress in bearing lubrication performance, and further summarizes the research on hydro-turbine rotor system dynamic characteristics, including the modal characteristics and dynamic response characteristics. Finally, this paper summarizes the main research progress of the hydro-turbine rotor system and proposes possible directions in future research. Literature review shows that the hydro-turbine runners and bearings have achieved multi-field coupling analysis of three-dimensional (3D) models, and some work on multi-field coupling of rotor systems has been carried out. The transition of 3D multi-field coupling from single component to rotor system is significant to accurately predict the rotor system dynamic characteristics and the solution of engineering problems, which requires further in-depth research on the multi-field coupling theory, numerical methods, 3D model integrity, simulation software, etc., and the spatiotemporal synergy between multi-fields should be fully considered.

Review on the mechanism of failure mode based on mechanical performance analysis of brake disc

The reliability and efficiency of brake discs are crucial for ensuring the safe operation of vehicles. With the growing demands of industrial applications and technological advancements, the mechanical performance and failure issues of brake discs have garnered extensive attention. To better understand the mechanisms affecting the mechanical performance and failure modes of brake discs, a comprehensive review of the influencing factors on their mechanical properties is presented. This includes an examination of the impact of brake disc structure, materials, and working conditions from both numerical simulation and experimental perspectives. Furthermore, the effects of temperature distribution and stress distribution on different failure modes of brake discs are summarized. Based on thermomechanical coupling theory, the failure modes under varying temperature and stress conditions are analyzed. Finally, considering the current research status of brake discs, in-depth mechanical performance analysis and failure mode studies can provide significant theoretical and practical guidance for designing more durable and safer brake discs.

Coupled Point Defect Theory and Artificial Neural Network Studying Dynamic Behaviors of Rebar Corrosion

The degradation of reinforced concrete structures remains a serious issue in infrastructural systems, such as buildings, highways, and bridges. The problem is caused by the presence of chloride, either from being present in the concrete mix (e.g., from the use of brackish water or the addition of CaCl2 as a “setting agent”) or by ingress from the external environment (e.g., road salt or marine environments). A metric known as the chloride threshold (CT) has been developed to describe the susceptibility of the steel to chloride-induced passivity breakdown. Despite the widespread use of CT as a metric for describing the impact of chloride on the corrosion of rebar, a theoretical basis for this metric does not appear to have been established. In addition, the CT is a highly distributed parameter, reflecting the practical difficulty in controlling or measuring various environmental parameters in concrete and in reliably detecting passivity breakdown. Therefore, we have conducted several tasks to theoretically and practically understand how rebar corrosion is dependent on CT. We have established a rich database of CT and its associated primary and secondary influencing factors, in which each vector of CT includes about 20 variables. Statistical analyses reveal that CT is lognormally distributed whereas potential parameters are normally distributed. We developed a suitable theoretical basis, so that CT can be effectively related to the properties of the steel in the passive state and to its susceptibility to chloride-induced passivity breakdown. We also demonstrated that it is possible to calculate CT in pure, empirical manner using Artificial Intelligence (AI) techniques, in in accordance with theoretical prediction, through trained artificial neural network which was trained based on the CT database. However, a significant amount of work remains to be completed in the future in developing an understanding of steel corrosion in concrete. Our knowledge of underlying factors that control the CT is still very poor due to the paucity of accurate data in the literature, and it is ultimately insufficient to provide a more accurate estimate of CT than that obtained by either the ANN prediction or point defect theory analysis at this stage.

Analysis Method of the Coupling Relationship Between Big Data Sports Industry Development and Economy

This paper studies the dynamic interaction between sports industry and urbanization process. Based on grey system theory and agglomeration economy theory, this paper studies the correlation and coupling between sports industry and urbanization in Shanghai and establishes the correlation and evolution relationship between them. Sports industry has played a key role in urban infrastructure construction, spatial layout optimization and industrial structure transformation. Research shows that e-sports industry is closely related to urbanization, and it is the product of technological innovation, industrial integration and capital flow. Industrial development and urbanization show a “U” curve, especially in 2014-2017. Coupling theory extends from the field of physics to the field of sociology, which provides a framework for evaluating the degree of interaction between multiple systems. By investigating the coupling between urbanization and sports industry, this study aims to reveal the intricate relationship between urbanization and sports industry.

Ordering Effect of Charge-Charge Repulsion in Doped Antiferromagnetic Lattices: A Coupled Cluster Study.

In quantum chemistry, single-reference Coupled Cluster theory, and its refinements introduced by Bartlett, has become a "gold-standard" predictive method for taking into account electronic correlations in molecules. In this article, we introduce a new formalism based on a Coupled Cluster expansion of the wave function that is suited to describe model periodic systems and apply this methodology to the case of hole-doped antiferromagnetic two-dimensional (2D)-square spin-lattices as a proof of concept. More precisely, we focus our study on 1/5 and 1/7 doping ratios and discuss the possible ordering effect due to large hole-hole repulsion. Starting from one of the equivalent single determinants exhibiting a full spin alternation and the most remote location of the holes as a single reference, the method incorporates some corrections to the traditional Coupled Cluster formalism to take into account the nonadditivity of excitation energies to multiply excited determinants. The amplitudes of the excitations, which are possible on the excited determinants but impossible on the reference, are evaluated perturbatively, while their effect is treated as a dressing in the basic equations. The expansion does not show any sign of divergence of the wave operator. Finally, the probabilities of holes moving toward the first- and second-neighboring sites are reported, which confirms the importance of the hole-hole repulsion and offers a picture of how stripes expand around its central line in the "stripe phases" observed in cuprates.