Model Potential Method Research Articles

Effect of an edge dislocation on hydride growth in zirconium: elastic complex potential study

The formation of hydrides can significantly decrease the mechanical reliability of Zr servicing in the nuclear reactor. This study investigates the effect of the local stress field resulting from the hydride eigenstrain and dislocations on hydrogen transport and explores the hydride growth regulation. The stress functions, which can be extended and further applied to the realistic crystal structure and servicing status, are derived using the dislocation-based strain nucleus model and elastic complex potential method. The nonhomogeneous equation of hydrogen transport governed by diffusion and hydrostatic stress gradient is analytically solved. The results show that: (1) In the absence of dislocations, the hydride grows toward 112¯0 direction under the hydrostatic stress gradient resulting from the hydride eigenstrain. (2) The lower the temperature is, the higher the hydrogen concentration gradient in the adjacent area of the hydride is. The higher hydrogen fraction can also accelerate the growth rate. (3) Dislocation defects are capable of inducing triangle-shaped and asymmetric growth tendencies and providing new nucleation loci for hydrides. Based on the significant hydrostatic stress gradient led by dislocation singularity, this study analytically explains the autocatalysis and new-nucleation-locus effects raised by the in-situ observations.

Development of CRISPR Cas9, spin-off technologies and their application in model construction and potential therapeutic methods of Parkinson's disease.

Parkinson's disease (PD) is one of the most common degenerative diseases. It is most typically characterized by neuronal death following the accumulation of Lewis inclusions in dopaminergic neurons in the substantia nigra region, with clinical symptoms such as motor retardation, autonomic dysfunction, and dystonia spasms. The exact molecular mechanism of its pathogenesis has not been revealed up to now. And there is a lack of effective treatments for PD, which places a burden on patients, families, and society. CRISPR Cas9 is a powerful technology to modify target genomic sequence with rapid development. More and more scientists utilized this technique to perform research associated neurodegenerative disease including PD. However, the complexity involved makes it urgent to organize and summarize the existing findings to facilitate a clearer understanding. In this review, we described the development of CRISPR Cas9 technology and the latest spin-off gene editing systems. Then we focused on the application of CRISPR Cas9 technology in PD research, summarizing the construction of the novel PD-related medical models including cellular models, small animal models, large mammal models. We also discussed new directions and target molecules related to the use of CRISPR Cas9 for PD treatment from the above models. Finally, we proposed the view about the directions for the development and optimization of the CRISPR Cas9 technology system, and its application to PD and gene therapy in the future. All these results provided a valuable reference and enhanced in understanding for studying PD.

Convergence of Electronic Structure Properties in Ionic Oxides Within a Fragment Approach

Embedded-cluster models of crystalline solids are important to allow accurate wave function methods to be applicable to solids. The ab-initio model potential method, in which the crystal is divided into three different fragments, one quantum fragment, one ab-initio model potential fragment and one point-charge fragment, has historically been shown to be a viable tool for describing the electronic structure in ionic solids. The optimal size of these regions is, of course, individual for each crystal. In this study we analyzed the convergence of the electronic structure properties with respect to an increase of the size of the quantum part and the layer of potentials. MgO crystal and Ni: MgO were used for this purpose as examples of an ideal crystal and a crystal with a point defect. We demonstrated that with an increase of the cluster size, the electron density in the inner part of the cluster becomes very similar to the electron density in the periodic model. Clusters, embedded into a layer of model potential and electrostatic field, are a good alternative to periodic description.

A program system for self-consistent embedded potentials for ionic crystals

Embedded-cluster models of crystalline solids are important to allow accurate wave function methods to be applicable to solids. The ab initio model potential method for embedding ionic solids has historically been shown to be a viable tool. While useful, the method has been limited by the need to generate such potentials for each crystal structure and the lack of a freely available program for generating ab initio model potentials. Herein, this is remedied by showcasing a new, AFL licensed, program, SCEPIC, which can be used in combination with Molcas or OpenMolcas codes to derive ab initio model potentials for ionic crystals.The applicability of ab initio model potentials derived via SCEPIC is evaluated for three simple ionic solids: MgO, CaO and CaF2. The following questions are addressed: (i) the capability of the method to reproduce the density matrix from periodic density functional theory calculations, (ii) the feasibility of performing geometry optimisations, (iii) the possibility to model band gaps of insulators and (iv) the ligand-field splitting of Ni-doped MgO. Going beyond the classical restriction of parametrising ab initio model potentials only at the Hartree–Fock level-of-theory, this work additionally address the sensitivity of results to the underlying Hamiltonian used to derive the potentials. The results demonstrate that good agreement with periodic density functional theory calculations can be achieved, geometry optimisations are feasible and accurate band gaps and ligand-field splittings can be computed.

Study of hanging valley in loess-paleosoil sediments with soil erosion assessment using nuclear and erosion potential methods

This paper is dealing with soil erosion assessment using two different approaches: nuclear model and erosion potential method, also known as Gavrilovic's method. Complex valley systems on Titel Loess Plateau were selected for investigation. Radiocaesium is favored in many studies as an optimal erosion tracer due to its relatively long half-life, negligible renewal in the environment and strongly binding ability onto soil particles. The use of gamma-spectrometry in environmental testing laboratories acts as a precise and fast measurement technique for determination of 137Cs activity concentrations, without the need for complicate preparation of samples. Annual erosion and deposition rates were estimated according to three conversion models for uncultivated land: the profile distribution model with two years of dominant fallout of 137Cs (1963 and 1986) and the diffusion and migration model using WALLING software. The applied nuclear models were validated by comparison with erosion potential model which is the most relevant empirical model for erosion processes in torrent valleys. The obtained results indicate a good agreement with overall low values of average annual soil erosion rates on all soil profiles in the investigated area. Correlation analysis has determined the different influence of slope, terrain curvature, and vegetation index on the erosion models.

NUMERICAL STUDYING ENERGY PARAMETERS OF MULTIELECTRON ATOM IN A MAGNETIC FIELD: HELIUM

There are presented the results of calculating the energies of the helium atom energy in a homogeneous magnetic field on the basis of the new numerical quantum-mechanical approach. The approach is based on the numerical difference solution of the Schrödinger equation, the model potential method and the operator perturbation theory formalism. The obtained results on energy of the helium atom in dependence upon the magnetic field strength are compared with available theoretical results, obtained on the basis of alternative numerical Hartree-Fock and diagonalization methods.

Calculation of Pairwise Effective Potentials in the Disordered Ni-22.5at.%Fe Alloy Using Model Potential Method with Account of Size Effect

Pairwise effective potentials in first seventeen shells of the Ni-22.5at.%Fe alloy are calculated using model potential method with account of the linear size effect. Using obtained values of pairwise effective potentials, the short range order parameters on the first seventeen shells of alloy are calculated by Krivoglaz-Clapp-Moss method. The calculated values ​​of the short-range order parameters were fitted to the experimental values ​​by varying the parameters of static atomic displacements. Reliable value of critical temperature of order-disorder phase transition in Ni-22.5at.%Fe alloy was calculated using obtained meanings of pairwise effective potentials.

A new approach to study electron and positron scattering from acetylene

Studies on electron and positron scattering from acetylene are very important for their applications in the plasma and astronomical environments. In view of such importance, we have performed the cross section calculations for electron and positron scattering from acetylene molecule using the optical model potential method with an analytically obtained static potential. In the present study, the charge cloud of acetylene is represented through multi-center Gaussian wavefunctions and using the same, static potential seen by the projectile electron/positron is evaluated analytically with a new approach. A complex optical potential consisting of our analytical static potential with the appropriate exchange, polarization and absorption potentials has been obtained. Using this complex potential in the Schrodinger equation and utilizing partial wave analysis technique, the scattering phase shifts are evaluated for the electron and positron collisions with the acetylene molecule. Differential, integral, momentum transfer, absorption and total cross sections have been calculated for the incident projectile energies in the range 10−500 eV. The obtained results are compared with the previous available theoretical and experimental results, which show good agreement and thus demonstrate the applicability of our method.

Model-potential method for high-order harmonic generation in monolayer graphene

We develop a model potential to simulate the effective potential of a single active electron in monolayer graphene by taking the electron energy band structure calculated by the density functional theory (DFT) as a reference. Based on the single-electron Schr\"odinger equation, the model potential is used to calculate not only the energy band structure but also the transition dipole moment, charge density, and other physical quantities of graphene. These quantities are compared with results from DFT and a good consistency is achieved. The simulation of laser-graphene interaction with the same laser parameters as Yoshikawa et al. [Science 356, 736 (2017)] is performed with the time-dependent Schr\"odinger equation. The obtained driving laser ellipticity scaling, the harmonic ellipticity, and the harmonic major-axis angle can well reproduce the experimental results. It is found that the carrier-envelope phase and chirp effects are capable of regulating high-order harmonic generation in monolayer graphene. The model potential method can be extended to field-free calculations and dynamic simulations in other materials as long as the corresponding model potential is constructed.

Расчет энергий упорядочения методом модельного потенциала с учетом линейного размерного эффекта в сплаве Ni-14at.%Pt

Расчет энергий упорядочения методом модельного потенциала с учетом линейного размерного эффекта в сплаве Ni-14at.%Pt

New Method for Calculating Pairwise Effective Potential in Binary Solid Solutions

A new method for calculating the pairwise effective potential on arbitrary shells of the binary disordered solid solutions is proposed with account for the linear size effect. The method is based on the fitting of the order–disorder temperature calculated by the model potential method to its known experimental value. In disordered Cu $${}_{3}$$ Au alloy, the pairwise effective potential is calculated and the short-range order parameters on the first fourteen shells are estimated using the Krivoglaz–Clapp–Moss method. A satisfactory coincidence with the experimental data is obtained.

DYNAMICAL AND TOPOLOGICAL INVARIANTS OF PbO DYNAMICS IN A RESONANT ELECTROMAGNETIC FIELD

Nonlinear chaotic dynamics of the PbO molecule interacting with a resonant linearly polarized electromagnetic field is computed within the quantum model, based on the numerical solution of the Schrodinger equation and model potential method. To calculate the system dynamics in a chaotic regime the known chaos theory and non-linear analysis methods such as a correlation integral algorithm, the Lyapunov’s exponents and Kolmogorov entropy analysis are used. There are listed the data of computing dynamical and topological invariants such as the correlation, embedding and Kaplan-Yorke dimensions, Lyapunov’s exponents, Kolmogorov entropy etc..

SPECTROSCOPY AND DYNAMICS OF MULTIELECTRON ATOM IN A MAGNETIC FIELD: NEW APPROACH

Spectroscopy and dynamics of multielectron atomic system in a magnetic field is numerically investigated. It is presented a new quantum-mechanical approach to calculating the energies and widths of some states for the multi-electron atomic system in in a homogeneous magnetic field. The approach is based on the numerical difference solution of the Schrödinger equation, the model potential method and the operator perturbation theory formalism. As illustration, the data for energies of the electronic excited and ground state of the lithium atom in dependence upon the magnetic field strength are listed and compared with available theoretical results, obtained on the basis of alternative Hartree-Fock method.

Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules using a Gaussian basis

A model-potential method is employed to calculate binding, elastic scattering, and annihilation of positrons for a number of atoms and small nonpolar molecules, namely, Be, Mg, He, Ar, H$_2$, N$_2$, Cl$_2$, and CH$_4$. The model potential contains one free parameter for each type of atom within the target. Its values are chosen to reproduce existing ab initio positron-atom binding energies or scattering phase shifts. The calculations are performed using a Gaussian basis for the positron states, and we show how to obtain values of the scattering phase shifts and normalized annihilation rate $Z_{\rm eff}$ from discrete positive-energy pseudostates. Good agreement between the present results and existing calculations and experimental data, where available, is obtained, including the $Z_{\rm eff}$ value for CH$_4$, which is strongly enhanced by a low-lying virtual positron state. An exception is the room-temperature value of $Z_{\rm eff}$ for Cl$_2$, for which the present value is much smaller than the experimental value obtained over 50 years ago. Our calculations predict that among the molecular targets studied, only Cl$_2$ might support a bound state for the positron, with a binding energy of a few meV.

Research on the Spatial Features of the E-RetailingEconomic Linkages at County Level: A Case Study for Zhejiang Province, China

Quantitatively evaluating the spatial characteristics of regional e-retailing economy linkages is of great significance for clarifying the spatial organization of regional e-retailing economies, and promoting regional coordinated development. However, due to the lack of study data, it is difficult toconduct quantitative research on these regional e-retailing economic linkages. Taking advantage of emerging new data sources, the depth and breadth of related research cannow be improved. This paper considers 64 county-level economic areas in Zhejiang Province as network nodes.A revised gravity model was used to measure the intensity of the e-retailing economic linkage in 2016,based upon the e-retailing data provided by the Department of Commerce of Zhejiang Province, China. On this basis, the geographic information system (GIS) tool, a model-potential method and a social network, were used to analyze the spatial features of the e-retail economic linkages at the countylevel in Zhejiang Province. The results showed that the spatial polarization of the economic linkage pattern emerged as prominent, with the overall difference and east-west gradient difference between counties proving significant. In addition, the major linking partners of most regions were relatively singular, and a problem of vulnerability in e-retail economic development was shown.Secondly, the southwest region of Zhejiang Province was an important obstacle in the integration process of regional e-retail economy, through analyzing the connection scope of e-retailing economics. Thirdly, the central Zhejiang subgroupwas a key plate connecting east and west, which plays an importantlinking role in the development of regional equalizationwhen we analyzethe cohesive subgroup pattern. Inspired by this, we hypothesized that a microscopic analysis results of Zhejiang Province could provide some enlightenment for the balanced and integrated development of China’s regional e-retailing economy.

ХАОТИЧНА ДИНАМІКА ДВОАТОМНИХ МОЛЕКУЛВ ЕЛЕКТРОМАГНІТНОМУ ПОЛІ

Nonlinear chaotic dynamics of the diatomic molecules interacting with a resonant linearly polarized electromagnetic field is computationally modelled. It is presented an effective quantum-mechanical model for diatomic molecule in an electromagnetic field, based on the Schrodinger equation and model potential method. To detect the elements of a chaotic dynamics, we used the known chaos theory and non-linear analysis methods such as a correlation integral algorithm, the Lyapunov’s exponents and Kolmogorov entropy analysis, prediction model etc. There are listed the data of computing dynamical and topological invariants such as the correlation, embedding and Kaplan-Yorke dimensions, Lyapunov’s exponents, Kolmogorov entropy etc, for polarization time series of the ZrO molecule interacting with a linearly polarized electromagnetic field. The results obtained are in a physically reasonable agreement with the conclusions by Berman, Kolovskii, Zaslavsky, Zganh et al, Glushkov et al.

Theoretical study of the low-lying adiabatic states of the NaLi+ molecular ion

With one active electron, the NaLi+ cation is a relatively simple system to study, and a good candidate for which results issue from different approaches can be compared to cross check the reliability of different theoretical methods for the calculation of the adiabatic potential energies. However, comparison of the ab initio results of Berriche (2003) and those of Magnier and Frécon (2001), employing model potential methods, is showing a serious disagreement concerning several molecular states. In particular, the low-lying states 22Σ+,42Σ+,62Σ+,82Σ+,102Σ+ and 42Π obtained by Magnier and Frécon, are found to be repulsive whereas they are attractive when ab initio methods are used.To clarify the origin of such a disagreement, in this work, the NaLi+ cation is re-investigated within the framework of the model potential approach. Adiabatic energies and corresponding molecular spectroscopic constants of states dissociating up to the limit Li++Na(4d) are computed. A good agreement with the previous ab initio calculations is observed.

A revised study of the [formula omitted] alkali-dimer using a model potential approach

The model potential approach is well adapted to study atomic and molecular systems involving a single active electron. Such is the case of the alkali-dimer lithium cation Li2+. However, a comparison of the model potential results of Magnier et al. (1999) and those based on ab initio techniques (Bouzouita et al., 2006; Jasik et al., 2007, Musial et al., 2015) raises a number of questions related to the existence of an important disagreement regarding several excited states,which are found to be repulsive by Magnier et al. (1999) but attractive when ab initio techniques are employed.In this paper, we propose to re-investigate the Li2+ system, using a model potential technique to compute the adiabatic energy curves and the molecular spectroscopic constants. Our aim is to clarify whether this disagreement between the ab initio and model potential methods originates from some conceptual defect of the model potential technique or whether there is some source of error in the calculations of Magnier et al. (1999).

Structure and transport properties of the liquid Al80Cu20 alloy – A molecular dynamics study

Structural and transport properties of the liquid Al80Cu20 alloy have been investigated performing molecular dynamics simulations using a new parametrization of modified embedded atom model (MEAM) potential method retained to the available ab initio molecular dynamics (AIMD) and experimental data. Local atomic structural changes, including chemistry and topology, have been studied and discussed with the literature data. Strong chemical bonding of unlike atoms in comparison to like-ones is found and confirmed by the available literature data. High degree of topological complexity and icosahedron-like type atomic clusters of increasing abundance with temperature decrease are observed, and their influence on short-range chemical ordering as well as transport properties have been defined. Almost perfect agreement between experimental data and the presented MEAM-MD simulations has been registered for the self-diffusion coefficient of Cu atoms in comparison to significant underestimation of experimentally determined inter-diffusion coefficient of the liquid Al80Cu20 alloy. Viscosities simulated, using two MD-based methods, exhibit a slight overestimation of experimental data.

DYNAMICS OF RADIATIVE TRANSITIONS BETWEEN STARK SUBLEVELS FOR NON-HYDROGENIC ATOMS AND DIATOMICS IN DC ELECTRIC FIELD

The quantum approach for definition of the radiation transitions between Stark sublevels for non-hydrogenic atoms and diatomics in an external electric field is underlined and based on the operator perturbation theory and model potential method. The cited radiative phenomena can be basis for construction of new types of the quantum sensor devices.