Method For Structure Calculations Research Articles

Adaptive Anderson mixing for electronic structure calculations

Convergence rates of iterative algorithms for solving non-linear fixed-point (or root-finding) problems depend on the quality of the solution guess done in each iteration, which is used as the starting value in the next step. To avoid instabilities and oscillations, that guess is usually constructed (mixed) as a linear combination of the newly calculated value with values from the previous iterations. The mixing algorithm constitutes a crucial component for electronic structure calculation methods based on iterative seeking for a self-consistent state. This paper reviews several mixing algorithms for electronic structure calculations. The most important numerically confirmed finding is that the calculation speed depends more on the choice of the so-called “mixing coefficient” than on the choice of a particular algorithm. Then a new method allowing an automatic adaptation of this coefficient is proposed, implemented, and tested on various solid-state structures within three electronic structure calculation codes. In our testing cases, the newly designed Adaptive Anderson Algorithm exhibits better convergence for a broader range of initial mixing coefficients, and similar or better robustness, in comparison to the standard Anderson method. The Fortran implementation of the new algorithm and its Python wrapper are briefly described in the paper and made available for public use.

Flexible Riser Tensile Armor Modelling Method and Application to Fatigue Analysis

In this paper, we present a new stress calculation method for flexible structures, particularly, tensile armors, and apply it to flexible riser fatigue analysis. The method is based on a 3-dimensional curved bar theory. First, the tensile armor center line was described as a cylindrical helix curve; its bent curve length and bending migration length were derived and studied under different friction scenarios. Second, the tensile and bending stiffness was derived with consideration of more accurate shape parameters and the frictional hysteretic effect, and verified through FEA analysis results. Third, we presented the stress calculation formula for tensile armor under tension and bending load. All stress components were considered, including tensile, bending and shear stresses. Fourth, the method was benchmarked with published experimental results on a flexible prototype tension and bending tests, and comparisons showed general agreements. Fifth, the method was applied to an in-service 8″ flexible riser for fatigue assessment and lifetime extension evaluation, and showed the flexible riser has sufficient remaining fatigue life, and is suitable to continue its service under the current operating conditions. Last, conclusions were drawn. We concluded that the presented tensile armor stress calculation method and modelling techniques are valid for flexible riser fatigue analysis. This method is time efficient, and can be implemented into other multi-scale models for riser dynamic analysis. It is also applicable to other similar helix structure stress analysis, such as wire ropes, submarine hoses, and subsea umbilicals.

Adaptive multigrid method for quantum eigenvalue problems

In this paper, a new type of adaptive finite element method is proposed for nonlinear eigenvalue problems in electronic structure calculations based on the multilevel correction method and adaptive multigrid method. Different from the classical adaptive finite element method for electronic structure calculations which needs to solve a nonlinear eigenvalue model directly in each adaptive finite element space, our approach only needs to solve a linear elliptic boundary value problem by adaptive multigrid method in each adaptive space, and then correct the eigenpair approximation by solving a small-scale nonlinear eigenvalue model in a low-dimensional correction space. Since solving large-scale nonlinear eigenvalue model is avoided which has exponentially increased computational time, the efficiency of electronic structure calculations can be improved evidently. In addition, the corresponding convergence analysis of the proposed adaptive multigrid algorithm are also derived theoretically and numerically.

Modeling of thermo-elastic properties of composite material in stability problems of multilayered shells

Thin-walled structures, the elements of which are plates and shells made of composite materials, are increasingly used in various industries. The growing needs of practice and the introduction of new composite materials require further improvement of the calculation methods of shell structures of inhomogeneous structure. Therefore, the problem of developing an adequate method of analyzing the behavior of shells made of composite materials with a multilayer structure is relevant. The work is devoted to the application of the developed method of finite elements for the analysis of geometrically nonlinear deformation and stability of elastic shells to the problem of the study of shells, the layer materials of which are composites of a fibrous structure. The method of structuring materials through the shell thickness and plan by using a universal 3D finite element is applied to model the thermoelastic properties of a ingomogeneous material. Determination of the effective characteristics of the composite material is realized by the structural micromechanical parameters of its components based on known methods of predicting elastic constants for this model of the composite material. The multilayer finite element, created within the framework of the developed approach, can be exploited to the problems of calculating thin elastic shells from both traditional and composite materials. The results of investigation of a multilayer composite panel using various micromechanical techniques are presented. The results of the study of a multilayer composite panel obtained by various micromechanical methods are given. These results are consistent with those obtained using the NASTRAN software. The new modification of the developed finite element makes it possible to analyze the stress-strain state and stability of multi-layer shells made of fibrous composite materials reliably, with accuracy acceptable for engineering calculations.

Nonlocal correlation effects due to virtual spin-flip processes in itinerant electron ferromagnets

We present an ab initio method for electronic structure calculations, which accounts for the interaction of electrons and magnons in ferromagnets. While it is based on a many-body perturbation theory we approximate numerically complex quantities with quantities from time-dependent density functional theory. This results in a simple and affordable algorithm which allows us to consider more complex materials than those usually studied in this context ($3d$ ferromagnets) while still being able to account for the nonlocality of the self-energy. Furthermore, our approach allows for a relatively simple way to incorporate self-consistency. Our results are in a good agreement with experimental and theoretical findings for iron and nickel. Especially the experimental exchange splitting of nickel is predicted accurately within our theory. Additionally, we study the half-metallic ferromagnet NiMnSb concerning its nonquasiparticle states appearing in the band gap due to spin-flip excitations.

Analysis and Experimental Research on Vibration Characteristics of Pressure Shell Structure

The vibration and sound radiation characteristics of the submarine pressure hull structure are important performance indicators for the acoustic design of the submarine structure. In this paper, the spectral element method is used to analyze the vibration of the shell structure. Combined with the periodic structure theory, the theoretical calculation method of the periodic ribbed shell structure is deduced, and the analytical method that can be used to calculate the vibration of the pressure shell structure is established. The feasibility of applying the spectral element method to the vibration calculation of the pressure shell structure is verified by comparing the analytical calculation and the finite element simulation. The vibration characteristics test experiment of the actual submarine pressured hull structure is carried out. The results show that the theoretical analysis is correct.HighlightsThe vibration and sound radiation characteristics of the submarine pressure hull structure have an important influence on the radiated noise of the submarine.A theoretical analysis method of vibration characteristics of pressure hulled based on spectral element method and periodic structure theory is proposed.The experimental study on vibration characteristics and active control of line spectrum of the pressure hull is carried out.

Truncated atomic plane wave method for subband structure calculations of moiré systems

We propose a highly efficient and accurate numerical scheme named the truncated atomic plane wave method to determine the subband structure of twisted bilayer graphene (TBG) inspired by the Bistritzer-MacDonald model. Our method utilizes real-space information of carbon atoms in the moir\'e unit cell and projects the full tight-binding Hamiltonian into a much smaller subspace using atomic plane waves. Using our method, we are able to present accurate electronic band structures of TBG in a wide range of twist angles together with the detailed moir\'e potential and screened Coulomb interaction at the first magic angle. Furthermore, we generalize our formalism to solve the problem of low-frequency moir\'e phonons in TBG.

Shape Memory Alloy-Spring Pendulum for Vibration Suppression of Wind-Induced Transmission Tower-Line Systems

Wind-induced vibration suppression of transmission line structures is critical for structural reliability and serviceability. In this study, a shape memory alloy-spring pendulum (SMA-SP) is proposed for a wind-induced tower-line system to improve the reliability and serviceability of the control unit. A numerical calculation method of the transmission tower line structure coupled with the SMA-SP is established with special emphasis on the solid elements of the damper. Furthermore, the effectiveness and reliability of vibration suppression on wind-induced transmission line structures are evaluated and parametric analyses are conducted; the results reveal the influences of key parameters on the performance of SMA-SP and provide design recommendations for applications. In this study, it is demonstrated that the SMA-SP provides more stable control effects on the wind-induced vibration of transmission line structures than a conventional spring pendulum (SP), and the proposed numerical method effectively demonstrates the nonlinear mechanism of the damper. The parametric analyses show that SMA-SP exhibits low sensitivity levels to variations in the tuning frequency ratio and achieves optimal reduction effects after satisfying the internal resonance condition.

Coevolution mechanism and branch of pillar‐overburden fissures in shallow coal seam mining

AbstractThe large‐scale mining of coal resources promotes the formation of section coal pillar groups between working faces. The overlying strata are supported by coal pillars, which leads to the formation of a unique fracture‐bearing structure in the key stratum, resulting in the evolution of fissures (cracks) and a generally high load on the supports. Studying the fracture‐bearing structure formed by coal pillars and overlying strata (fissures) is the basis for realizing rational mining of working faces. Here, the evolution characteristics of coal pillar‐overburden rock (fissures) in shallow coal seam mining and the working resistance of the support with stable fracture bearing structure of section coal pillar and overburden rock were studied in the No. 1‐2 coal mining of Longhua Coal Mine in Shenmu City, Northern Shaanxi. The fissure evolution characteristics on both sides of the coal pillar and the fracture‐bearing structure of the rock stratum were obtained by physical similarity simulation experiment. The mechanical calculation model of the coal pillar‐overburden rock (fissure) structure was established by theoretical derivation and calculation, and the working resistance of advanced support with a stable mechanical structure was studied. The research shows that the fracture evolution and rock fracture characteristics of a shallow coal seam mining face can be divided into three zones. Through the reanalysis of the mechanical structure of coal pillar‐overburden rock (fissure), the combined mechanical structure of the subkey stratum consisting of a lagging broken step rock beam structure and the main key stratum consisting of a hinged rock beam structure was obtained. Combined with the failure characteristics of the section coal pillar, a mechanical structure calculation method suitable for the bearing characteristics of section coal pillar support in shallow coal buried layers was obtained, and the field measurement results were verified.

Evaluation of tight-binding DFT performance for the description of organic photochromes properties.

Photochromic molecules are widely studied and developed for their many potential applications. To optimize the required properties through theoretical models, a considerable chemical space is to be explored, and their environment in devices is to be accounted for.. To this end, cheap and reliable computational methods can be powerful tools to steer synthetic developments. As ab initio methods remain costly for extensive studies (in terms of the size of the system and/or number of molecules), semiempirical methods such as density functional tight-binding (TB) could offer a good compromise between accuracy computational cost. However, these approaches necessitate benchmarking on the families of compounds of interest. Thus, the aim of the present study is to evaluate the accuracy of several key features calculated with TB methods (DFTB2, DFTB3, GFN2-xTB, and LC-DFTB2) for three sets of photochromic organic molecules: azobenzene (AZO), norbornadiene/quadricyclane (NBD/QC), and dithienylethene (DTE) derivatives. The features considered here are the optimized geometries, the difference in energy between the two isomers (ΔE), and of the energies of the first relevant excited states. All the TB results are compared to those obtained with DFT methods and state-of-the-art electronic structure calculation methods: DLPNO-CCSD(T) for ground states and DLPNO-STEOM-CCSD for excited states. Our results show that, overall, DFTB3 is the TB method leading to the best results for the geometries and the ΔE values and can be used alone for these purposes for NBD/QC and DTE derivatives. Single point calculations at the r2SCAN-3c level using TB geometries allow circumventing the deficiencies of the TB methods in the AZO series. For electronic transition calculations, the range separated LC-DFTB2 method is the most accurate TB method tested for AZO and NBD/QC derivatives, in close agreement with the reference.

Low Carbon Building Design Optimization Based on Intelligent Energy Management System

The construction of relevant standards for building carbon emission assessment in China has just started, and the quantitative analysis method and evaluation system are still imperfect, which hinders the development of lowcarbon building design. Therefore, the use of intelligent energy management system is very necessary. The purpose of this paper is to explore the design optimization of low-carbon buildings based on intelligent energy management systems. Based on the proposed quantitative method of building carbon emission, this paper establishes the quota theoretical system of building carbon emission analysis, and develops the quota based carbon emission calculation software. Smart energy management system is a low-carbon energy-saving system based on the reference of largescale building energy-saving system and combined with energy consumption. It provides a fast and effective calculation tool for the quantitative evaluation of carbon emission of construction projects, so as to realize the carbon emission control and optimization in the early stage of architectural design and construction. On this basis, the evaluation, analysis and calculation method of building structure based on carbon reduction target is proposed, combined with the carbon emission quota management standard proposed in this paper. Taking small high-rise residential buildings as an example, this paper compares and analyzes different building structural systems from the perspectives of structural performance, economy and carbon emission level. It provides a reference for the design and evaluation of low-carbon building structures. The smart energy management system collects user energy use parameters. It uses time period and time sequence to obtain a large amount of data for analysis and integration, which provides users with intuitive energy consumption data. Compared with the traditional architectural design method, the industrialized construction method can save 589.22 megajoules (MJ) per square meter. Based on 29270 megajoules (MJ) per ton of standard coal, the construction area of the case is about 8000 m2, and the energy saving of residential buildings is 161.04 tons of standard coal. This research is of great significance in reducing the carbon emission intensity of buildings.

On theoretical calculation method for two-dimensional planar shock wave refractions

A theoretical calculation method for wave structures in the flow resulting from the interaction between the two-dimensional planar shock and the material interface is developed. First, the propagation of the shock wave on either side of the interface is analyzed, and two regular refraction types and three irregular ones are identified. Then, according to the relative speed of the perturbations on either side, three different interaction cases are established. Compared with the existing Catherasoo’s method, this method is improved in the following aspects: 1) the influence of the perturbation in the post-shock flow field on the interaction is taken into account, including its type and whether it can catch up and interact with the shock front; 2) the interactions between different waves are calculated mostly based on the exact solutions of the Euler equations, except those involving post-shock subsonic rarefaction waves. This method has been used to investigate the interaction of a Mach number 1.17 shock with an air/SF<sub>6</sub> interface, and give wave structures that accord with numerical results and existing experimental data. The angle between the transmitted shock and the horizontal direction is obtained to be in better agreement with experimental data than Catherasoo’s result, and more parameters are obtained, such as the reflected wave and the interface deflection angle. For cases involving a Mach number 2.00 shock with different material density ratios and interface inclination angles, comparisons between theoretical and numerical results show that our method can obtain the type of wave structure more accurately than Catherasoo’s method, and identify a refraction type in which the post-shock strong perturbation catches up with the shock front and a three-wave structure is formed, whereas Catherasoo’s method cannot handle this case. Thus, the results show that the improved method in this work has better applicability and higher accuracy than the existing method in identifying the type of wave structure, and can also provide more information about the wave structures.

Comparison of seismic structure design in the world

Aseismic performance is one of the important technical indexes of modern buildings, which has been written into the building codes in various countries. Aseismic structure design is to enhance the stability of the building structure, ensure the safety of the building when the earthquake disaster occurs, reduce the loss and casualties. Since ancient times, innovations have been made in the design of seismic structures worldwide, especially in areas with high earthquake incidence. It was found in the previous research that the calculation method and design of seismic structures in American and Chinese building codes are different. Based on the interest of aseismic design, this paper summarizes the traditional and new aseismic structures. This paper first introduces several commonly used aseismic structures, such as multi-storey masonry, frame and seismic wall construction. Then this paper introduces the characteristics and differences of aseismic structure design in different countries from the modern and ancient time dimensions. In the end, Finally, it is concluded that the seismic structures are different due to the differences of geography, culture and climate in various countries. We can learn from the seismic structure analysis of ancient buildings that Aseismic structure design does not have to resist earthquake, but can reduce the damage of earthquake to the building by reducing the seismic force of the building.

범죄피해자 구조금 산출 방법의 문제점 및 개선방안범죄피해자 구조금 산출 방법의 문제점 및 개선방안

In 2010, the ｢Crime Victims Aid Act｣ was abolished and the new ｢Crime Victims Protection Act｣ was enacted, bringing about continuous changes to the development of the crime victim aid system which is guaranteed as a basic right in the Constitution.
 In the Rescue Act, which was abolished due to this influence, the relief money paid to victims to be rescued was a fixed amount in the form of a consolation money, but in the later revised Protection Act, the concept of actual income or average income of rescue victims was introduced, a system was implemented to pay differential rescue funds according to the relationship between the rescue victim and the rescue target victim.
 Meanwhile, the amount of relief also continued to increase each year in line with the rise in average wages, and the target for disability relief was expanded from the previous 10th grade to the 14th grade.
 In addition, there have been many previous studies that the protection law needs to be revised as foreign spouse rescue and victims of incidents caused by negligence are excluded from the rescue target.
 In addition, there are several problems with the rescue system, but the first problem to be improved is the uniform calculation method of the rescue fund that does not consider the age of the rescue victim at the time of the incident.
 It has been pointed out that the relief funds received by the victims to be rescued are not fair due to these problems, the ranking of unmarried children over the age of 19 who live on the income of rescue victims is not reasonable, and it is very insufficient to guarantee their future life.
 Therefore, this study aims to suggest a plan to improve the structural fund calculation method that can fundamentally improve the problems of the structural fund system.

Performance of Screened-Exchange Functionals for Band Gaps and Lattice Constants of Crystals.

Kohn-Sham density functional theory is the most widely used method for electronic structure calculations of solid-state systems. The screened-exchange functionals developed following the influential work of Scuseria and co-workers in 2003-2006 have significantly improved the accuracy of the predictions of solid-state properties. This work assesses six screened-exchange density functionals for the prediction of 60 band gaps (database BG60) and 68 lattice constants (database LC68). The band gaps are calculated with both consistently calculated lattice constants and experimental lattice constants. Results for the nonlocal screened-exchange functionals are compared with those for six widely used or recently developed local functionals. The results show that all the screened-exchange functionals have smaller mean absolute errors (MAEs) than any of the local functionals. All the functionals except HLE17 overestimate (on average) the lattice constants, and M06-SX gives the best performance among the compared functionals, with a MAE of 0.051 Å. All the functionals underestimate (on average) the band gaps, and M06-SX outperforms all other functionals, with a MAE of 0.47 eV. M06-SX also has the lowest root-mean-squared error for both LC68 and BG60. For the subdatabases of BG60, M06-SX shows better performance for ionic crystals and systems with large band gaps, while HSE12s gives better results for semiconductors and systems with small band gaps. Overall, M06-SX shows the best performance for solid-state systems, followed by N12-SX and HSE12s. The best-performing local functionals are M06-L, revM06-L, and HLE17 for band gaps and M06-L and revM06-L for lattice constants. We found that M06-SX, revM06-L, and N12-SX not only are well optimized for a broad array of chemical properties but also have very good performance for the databases in this paper, making them well-suited for applications involving heterogeneous chemistry.

A novel tetrahedral spectral element method for Kohn-Sham model

High order computational approach for the electronic structure calculation is a long-standing research area. Among all the discretization methods, spectral element method stands out for its flexibility to capture the singularity and high accuracy from the spectral perspective. In this work, we propose a tetrahedral spectral element method for full-potential electronic structure calculation. In the method, a C0 space is constructed for the numerical solution, based on a modification of basis functions proposed in [L. Jia et al. (2022) [48]] with the aid of generalized Koornwider polynomials, and a special designed tetrahedral mesh. Moreover, the interpolation and visualization are developed to provide numerical insights of our method. To demonstrate its potential towards practical simulations, we apply our method for calculating ground states of given electronic structures using the Kohn-Sham model. The method consists of a combination of an imaginary time propagation method and a self-consistent field iteration. For accelerating the simulation, a p-multigrid solver is developed which takes the advantage of the high order property of our method. A number of numerical experiments validate the effectiveness of our method, i.e., the expected spectral accuracy can be observed from results, and convincing ground states of various atoms and molecules are obtained.

Singular boundary method for band structure calculations of in-plane waves in 2D phononic crystals

In this study, the singular boundary method, which is a boundary collocation method, is first employed to calculate the band structures of in-plane waves in two-dimensional phononic crystals. When a unit cell of a phononic crystal is considered, the whole boundaries, including the continuity and periodic boundaries are discretized by the singular boundary method. Then, a linear eigenvalue equation is derived. For a given frequency, an eigenvalue that involves the Block wave can be calculated. Therefore, by sweeping the frequencies, the band structure can be obtained. The accuracy, efficiency and convergence of the proposed method are tested by several numerical examples, and the results demonstrate that the singular boundary method can provide stable and efficient results for band structure calculations of in-plane waves in two-dimensional phononic crystals.

Heat flow data and thermal structure in northeastern Japan

New heat flow data corrected for climate change over Northeastern Japan were obtained using the temperature profile of the borehole of the High Sensitivity Seismograph Network (Hi-net). The obtained spatial distribution of heat flow shows low heat flow on the forearc side, high heat flow along the Ou Backbone Range, and low heat flow in the plains on the back-arc side. However, the distribution is not clearly divided into high and low heat flow along the VF front; for example, the low heat flow extends from near the northern Kitakami Mountains on the forearc side to the Ou Backbone Range crossing the VF, while the high heat flow extends to the central Kitakami Mountains and Sendai plain on the forearc side. In addition, a crustal temperature structure model was developed that considers into account the presence of sedimentary layers, the temperature dependence of thermal conductivity, and differences in heat generation due to lithology. There is a good correlation between this temperature structure and the lower limit of the seismogenic layer, which is between 400 and 450 °C. Compared to previous studies, the crustal thermal structure calculation method assumed is a model whose estimated temperature distribution is sensitive to structural differences; however, a more accurate estimation of the temperature structure is possible if detailed structural information is available. On the other hand, it seems necessary to treat fluid behavior in more detail in areas of high heat flow. However, the estimation of crustal temperature structure, especially in regions with thick sedimentary layers, is considered an improvement over the previous study.Graphical

Microinterface intensification in hydrogenation and air oxidation processes

Hydrogenations and air oxidations usually have low apparent reaction rate, generally controlled by mass transfer rate, and widely exist in the modern chemical manufacturing process. The key to increase the mass transfer rate is the reduction of the liquid film resistance 1/ k L a . In this work, the original concept of microinterface intensification for mass transfer and then for these reactions has been proposed. We derived the regulation model and set up the mathematical calculation method of micron-scale gas-liquid interface structure on mass transfer and reaction, designed the mechanical energy exchange device that can produce gas-liquid microinterface system on a large scale, and established the OMIS system which is able on line to measure the diameter and distribution of millions of microbubbles, interface area a and mass transfer film thickness δ M , as well as developed a series of microinterface intensified reactor systems (MIRs) for the applications of hydrogenation and air oxidation processes. It is believed that this research will provide an up-to-date development for the intensification of hydrogenation and air oxidation reactions.

Thorium dicarbide under high pressure and high temperature: Ab initio investigation

A systematic study on the structural stability of thorium dicarbide (ThC2) under hydrostatic compression has been carried out by exploiting the evolutionary structure search algorithm as implemented in the universal structure predictor: evolutionary Xtallography (USPEX) code in conjunction with the ab initio electronic band structure calculation method. At ambient conditions, ThC2 exists in a monoclinic crystallographic phase with space group (SG) C2/c. Our calculations under generalized gradient approximation (GGA) predict the high-pressure structural sequence of monoclinic-I (SG C2/c) → monoclinic-II (SG C2/m) → orthorhombic-I (SG Pmma) → orthorhombic-II (SG Immm) → hexagonal (SG P6/mmm) for this material with transition pressures of ∼3.3, 58.3, 191.6, and 255 GPa, respectively. Out of this theoretically predicted high-pressure structural phase transition sequence, only the first transition, i.e., monoclinic-I → monoclinic-II, could be compared with the available high-pressure experimental study by Guo et al. [Sci. Rep. 7, 45872 (2017)]. The theoretically determined phase transition qualitatively agrees with the experimental results [Y. Guo et al. Sci. Rep. 7, 45872 (2017)]. Interestingly, our predicted intermediate orthorhombic-I (SG Pmma) phase has an enthalpy lower than that of the previously predicted orthorhombic Cmmm phase by Guo et al. [Sci. Rep. 7, 45872 (2017)]. The high-pressure structural sequence so predicted through static lattice calculations has been further substantiated by confirming the elastic and lattice dynamic stability of each structure in the pressure regime of its structural stability. Additionally, the superconducting transition temperature for all these structures has been determined and it is found that the monoclinic-II (C2/m) phase has the highest transition temperature of 17 K at 5 GPa. Furthermore, the thermo-physical properties along with the temperature-induced phase transitions in ThC2 have also been investigated through both the lattice dynamic simulations (within quasi-harmonic approximation) and ab initio molecular dynamics simulations.