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[Display omitted] • Machine learning-based deep potentials were developed for molten LiCl, NaCl, and KCl. • It was demonstrated that deep potentials can achieve DFT accuracy. • The local structure and transport properties of these salts were investigated using deep potentials. • The results predicted by deep potentials matched well with the AIMD and experimental data. In this work, the local structure and transport properties of three typical alkali chlorides (LiCl, NaCl, and KCl) were investigated by our newly trained deep potentials (DPs). We extracted datasets from ab initio molecular dynamics (AIMD) calculations and used these to train and validate the DPs. Large-scale and long-time molecular dynamics simulations were performed over a wider range of temperatures than AIMD to confirm the reliability and generality of the DPs. We demonstrated that the generated DPs can serve as a powerful tool for simulating alkali chlorides; the DPs also provide results with accuracy that is comparable to that of AIMD and efficiency that is similar to that of empirical potentials. The partial radial distribution functions and angle distribution functions predicted using the DPs are in close agreement with those derived from AIMD. The estimated densities, self-diffusion coefficients, shear viscosities, and electrical conductivities also matched well with the AIMD and experimental data. This work provides confidence that DPs can be used to explore other systems, including mixtures of chlorides or entirely different salts. [ABSTRACT FROM AUTHOR]

Abstract KAPPA, an open-source software library for the computation of thermodynamic and transport properties in non-equilibrium gas flows and species production rates, is presented. Thermodynamic properties rely on custom databases which describe the characteristics of atoms and molecules and interaction features. Mixture thermodynamic properties are formulated from species quantities. Species production rates are based on elementary chemical reactions and vibrational energy transitions. Transport properties are derived from kinetic theory which provides relationships for transport coefficients depending on the flow model. Several levels of non-equilibrium flow description are implemented: the detailed state-to-state (STS) approach, multi-temperature and one-temperature models. Sets of transport coefficients depend on the deviation from equilibrium; in the state-to-state model, they include state-resolved diffusion coefficients for each pair of vibrational states. A highly modular, object-oriented application program interface (API) has been developed. The adopted object-oriented programming paradigm (OOP), along with the implemented models of state-resolved physico-chemical relaxation rates, is presented. The design of the library allows it to be easily included in existing CFD codes and is aimed at code reusability and readability. Program Title: KAPPA Program Files doi: http://dx.doi.org/10.17632/mrx9n35bvs.1 Licensing provisions: GNU General Public Licence, version 3. Programming language: C++; developed and tested with Intel Compiler v. 18.x and GNU. External routines/libraries: KAPPA must be linked to yaml-cpp [1] in order to read human-readable database files and to Armadillo [2] for solving algebraic linear systems. Nature of problem: Numerical computation of transport properties and rate exchange coefficients for non-equilibrium reacting flows. Solution method: Non-equilibrium reacting flow is treated by a rigorous state-to-state (STS) kinetic theory approach. Restrictions: At present, KAPPA is validated for computing transport properties and rate exchange coefficients using the state-to-state (STS) approach; 1- and 2-temperature models have still to be validated, but they are already implemented. C++ compiler is mandatory. Unusual features: KAPPA is an open-source object-oriented highly modular and easy-to-maintain C++ software library which implements rigorous mathematical kinetic theory models. Additional comments: KAPPA project adopts Git [3], a free and open source distributed version control system. A public repository dedicated to KAPPA project [4] has been created on github , a web-based hosting service for software development projects using git versioning system. Finally, a comprehensive documentation [5] is provided parsing source code comments by means of doxygen software [6]. References: [1] Yaml-cpp is a YAML parser and emitter in C++ matching the YAML 1.2 specification. https://github.com/jbeder/yaml-cpp. [2] Armadillo is a fast C++ matrix library with easy to use functions and syntax, deliberately similar to Matlab which uses template meta-programming techniques. https://sourceforge.net/projects/arma/files/armadillo-8.500.1.tar.zx. [3] Git, a free and open source distributed version control system. http://git-scm.com. [4] Github, a web-based hosting service for software development projects using git versioning system. https://github.com. [5] Official KAPPA documentation. https://github.com/lkampoli/kappa. [6] Doxygen, a documentation system for many programming languages. http://www.stack.nl/ dimitri/doxygen. [ABSTRACT FROM AUTHOR]

Abstract Understanding the effects of porous network characteristics including the percolation and tortuosity on transport properties of porous materials is of great importance for the design and optimization of such materials, e.g., for superior resistance to degradation due to the transfer of corrosive fluids. Meanwhile, the percolation and tortuosity of porous networks are strongly affected by the geometrical shape of pores. In this work, we devise a generic theoretical framework for the accurate predictions of the percolation threshold and tortuosity of porous networks and a variety of transport properties of two-phase porous materials composed of three-dimensional (3D) interpenetrating non-spherical pores randomly distributed in a homogeneous solid matrix. Our framework contains three major components: (1) a coupled scheme of Monte Carlo simulations and a rigorous excluded-volume percolation model for determining of the percolation threshold of porous networks; (2) a continuum percolation-based tortuosity model (CPTM) for deriving the geometrical tortuosity of porous networks near the percolation threshold and above; and (3) a continuum percolation-based generalized effective medium theory (CP-GEMT) for predicting various effective transport properties including the effective diffusivity, permeability, electrical and thermal conductivity of porous materials over the entire range of porosities. The theoretical framework yields accurate predictions of the percolation threshold, tortuosity and various effective transport properties, which are verified and validated using extensive experimental, numerical and analytical data for a wide spectrum of different porous materials reported in literature. Our framework is readily applicable to other non-spherical percolating networks composed of interpenetrating discrete objects like cracks, particles, interfaces, capsules and tunneling networks though 3D spherocylindrical porous networks are used as an introductory example in this work. Finally, we utilize the framework to explore the influences of the pore geometrical configurations on the tortuosity and effective diffusivity of porous materials. The results shed light on the intrinsic and complex interplay of components, structures and transport properties in porous materials, which in turn can provide novel insights for understanding degradation of porous materials in practical applications. [ABSTRACT FROM AUTHOR]

Dissipative particle dynamics (DPD) is a promising candidate technique for modeling rheological properties of soft matter systems. However, several methodological issues inhibit its exploitation as a computational rheology tool. In this work, we focus on the development of an automated method to compute transport properties from equilibrium simulation with particular attention to the assessment of the Green-Kubo approach reliability and computational feasibility for a large set of simple DPD systems with increasing Schmidt number. Furthermore, we investigate the time step size dependency of dynamic properties and the role of different time integration schemes. In particular, we assess the performance of the Shardlow-splitting algorithm against the most popular modified velocity-Verlet algorithm. We consider, for the first time, application of the Shardlow-splitting algorithm to the transverse DPD thermostat in different friction regimes relying on systematic numerical experiments. In addition, we make use of these findings to perform a multi-parametric study aiming to investigate the Schmidt number relationship with the effective friction coefficient. [ABSTRACT FROM AUTHOR]

Exploring the transport properties of different materials brings new avenue for basic understanding of emergent phenomena and practical applications in many different fields. Here, we report a program named as TRACK (TRA nsport properties for C orrelated materials using K ubo formalism) which is written in Python 3 for calculating temperature dependent electrical conductivity, electronic part of thermal conductivity, Seebeck coefficient and Lorenz number. In this code, Kubo linear-response formalism is utilized for computing these parameters using both interacting and non-interacting electronic structure methods. The formula for transport coefficients is accordingly modified to obtain the transport parameters under relaxation time approximation using band-theory. The basic inputs of this program are the structural information, dense k-points sampling in the irreducible part of the Brillouin zone and the information of velocity matrix elements, which can be calculated using third-party ab-initio package. TRACK is expected to calculate the transport properties of different class of materials. The code has been benchmarked by performing calculation on three different types of materials namely Vanadium (V), FeSi and LaCoO 3 , which are metal, semiconductor and Mott insulator, respectively. The temperature dependent behaviour of the transport coefficients for these materials show fairly good agreement with the corresponding experimental data. Program Title: TRACK CPC Library link to program files: https://doi.org/10.17632/jdt9tfkt4v.1 Developer's repository link: https://sourceforge.net/projects/track-code/files/TRACK.zip/download Licensing provisions: GPLv3 Programming language: Python3 External routines/libraries: NumPy, SciPy, Time Nature of problem: Calculating the transport parameters using the Kubo linear-response formalism. Solution method: We present a Python3 open source code for calculating transport coefficients using Kubo formalism. Both interacting and non-interacting electronic structure methodology are possible to be used for computing transport parameters. [ABSTRACT FROM AUTHOR]

Some statistical properties related to the diffusion in energy for an ensemble of classical particles in a bouncing ball model are studied. The particles are confined to bounce between two rigid walls. One of them is fixed while the other oscillates. The dynamics is described by a two dimensional nonlinear map for the velocity of the particle and time at the instant of the collision. Two different types of change of momentum are considered: (i) periodic due to a sine function and; (ii) stochastic. For elastic collisions case (i) leads to finite diffusion in energy while (ii) produces unlimited diffusion. On the other hand, inelastic collisions yield either (i) and (ii) to have limited diffusion. Scaling arguments are used to investigate some properties of the transport coefficient in the chaotic low energy region. Scaling exponents are also obtained for both conservative and dissipative case for cases (i) and (ii). We show that the parameter space has complicated structures either in Lyapunov as well as period coordinates. When stochasticity is introduced in the dynamics, we observed the destruction of the parameter space structures. [ABSTRACT FROM AUTHOR]

A new version release (2.0) of the molecular simulation tool ms 2 [S. Deublein et al., Comput. Phys. Commun. 182 (2011) 2350] is presented. Version 2.0 of ms 2 features a hybrid parallelization based on MPI and OpenMP for molecular dynamics simulation to achieve higher scalability. Furthermore, the formalism by Lustig [R. Lustig, Mol. Phys. 110 (2012) 3041] is implemented, allowing for a systematic sampling of Massieu potential derivatives in a single simulation run. Moreover, the Green–Kubo formalism is extended for the sampling of the electric conductivity and the residence time. To remove the restriction of the preceding version to electro-neutral molecules, Ewald summation is implemented to consider ionic long range interactions. Finally, the sampling of the radial distribution function is added. Program summary Program title: m s 2 Catalogue identifier: AEJF_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEJF_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 50375 No. of bytes in distributed program, including test data, etc.: 345786 Distribution format: tar.gz Programming language: Fortran90. Computer: The simulation program m s 2 is usable on a wide variety of platforms, from single processor machines to modern supercomputers. Operating system: Unix/Linux. Has the code been vectorized or parallelized?: Yes: Message Passing Interface (MPI) protocol and OpenMP Scalability is up to 2000 cores. RAM: m s 2 runs on single cores with 512 MB RAM. The memory demand rises with increasing number of cores used per node and increasing number of molecules. Classification: 7.7, 7.9, 12. External routines: Message Passing Interface (MPI) Catalogue identifier of previous version: AEJF_v1_0 Journal reference of previous version: Comput. Phys. Comm. 182 (2011) 2350 Does the new version supersede the previous version?: Yes. Nature of problem: Calculation of application oriented thermodynamic properties for fluids consisting of rigid molecules: vapor–liquid equilibria of pure fluids and multi-component mixtures, thermal and caloric data as well as transport properties. Solution method: Molecular dynamics, Monte Carlo, various classical ensembles, grand equilibrium method, Green–Kubo formalism, Lustig formalism Reasons for new version: The source code was extended to introduce new features. Summary of revisions: The new features of Version 2.0 include: Hybrid parallelization based on MPI and OpenMP for molecular dynamics simulation; Ewald summation for long range interactions; sampling of Massieu potential derivatives; extended Green–Kubo formalism for the sampling of the electric conductivity and the residence time; radial distribution function. Restrictions: None. The system size is user-defined. Typical problems addressed by m s 2 can be solved by simulating systems containing typically 1000–4000 molecules. Unusual features: Auxiliary feature tools are available for creating input files, analyzing simulation results and visualizing molecular trajectories. Additional comments: Sample makefiles for multiple operation platforms are provided. Documentation is provided with the installation package and is available at http://www.ms-2.de . Running time: The running time of m s 2 depends on the specified problem, the system size and the number of processes used in the simulation. E.g. running four processes on a “Nehalem” processor, simulations calculating vapor–liquid equilibrium data take between two and 12 hours, calculating transport properties between six and 24 hours. Note that the examples given above stand for the total running time as there is no post-processing of any kind involved in property calculations. [ABSTRACT FROM AUTHOR]

Rutile TiO2 nanoparticles were synthesized using co-precipitation method with an average diameter of ~30 nm TiO2 nanoparticle device was then fabricated on glass substrate. Aluminum electrodes were defined using photolithography and vacuum evaporation. A suspension of TiO2 nanoparticles was prepared in isopropanol using ultrasonic agitation. The nanoparticles were deposited between the electrodes. The device was tested by AC electrical measurements at 40%-90% relative humidity (RH). The impedance of the TiO2 nanoparticles decreases by about 80 times with the increase in RH from 40% to 90% at 100 Hz. The response time and the recovery time were 4 s and 5 s, respectively between 40% and 90% RH. At 100 Hz, the sensitivity of the aluminum electrode TiO2 nanoparticle device in the range of 40%-90% RH was 17 MΩ/%RH. Complex modulus analysis also confirms the increase in DC conductivity of TiO2 nanoparticles as RH increases. [ABSTRACT FROM AUTHOR]

Abstract: The numerical renormalization group is an efficient method to diagonalize model Hamiltonians describing correlated orbitals coupled to conduction states. While only the resulting eigenvalues are needed to calculate the thermodynamical properties for such models, matrix elements of Fermi operators must be evaluated before excitation and transport properties can be computed. The traditional procedure to calculate matrix elements is typically as expensive as the diagonalization of the model Hamiltonian. Here, we present a substantially faster alternative that demands much less memory, yields equally accurate matrix elements and is easier to code. [Copyright &y& Elsevier]

Abstract: This work presents the molecular simulation program ms2 that is designed for the calculation of thermodynamic properties of bulk fluids in equilibrium consisting of small electro-neutral molecules. ms2 features the two main molecular simulation techniques, molecular dynamics (MD) and Monte-Carlo. It supports the calculation of vapor–liquid equilibria of pure fluids and multi-component mixtures described by rigid molecular models on the basis of the grand equilibrium method. Furthermore, it is capable of sampling various classical ensembles and yields numerous thermodynamic properties. To evaluate the chemical potential, Widomʼs test molecule method and gradual insertion are implemented. Transport properties are determined by equilibrium MD simulations following the Green–Kubo formalism. ms2 is designed to meet the requirements of academia and industry, particularly achieving short response times and straightforward handling. It is written in Fortran90 and optimized for a fast execution on a broad range of computer architectures, spanning from single processor PCs over PC-clusters and vector computers to high-end parallel machines. The standard Message Passing Interface (MPI) is used for parallelization and ms2 is therefore easily portable to different computing platforms. Feature tools facilitate the interaction with the code and the interpretation of input and output files. The accuracy and reliability of ms2 has been shown for a large variety of fluids in preceding work. Program summary: Program title: ms2 Catalogue identifier: AEJF_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEJF_v1_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Special Licence supplied by the authors No. of lines in distributed program, including test data, etc.: 82 794 No. of bytes in distributed program, including test data, etc.: 793 705 Distribution format: tar.gz Programming language: Fortran90 Computer: The simulation tool ms2 is usable on a wide variety of platforms, from single processor machines over PC-clusters and vector computers to vector-parallel architectures. (Tested with Fortran compilers: gfortran, Intel, PathScale, Portland Group and Sun Studio.) Operating system: Unix/Linux, Windows Has the code been vectorized or parallelized?: Yes. Message Passing Interface (MPI) protocol Scalability. Excellent scalability up to 16 processors for molecular dynamics and >512 processors for Monte-Carlo simulations. RAM: ms2 runs on single processors with 512 MB RAM. The memory demand rises with increasing number of processors used per node and increasing number of molecules. Classification: 7.7, 7.9, 12 External routines: Message Passing Interface (MPI) Nature of problem: Calculation of application oriented thermodynamic properties for rigid electro-neutral molecules: vapor–liquid equilibria, thermal and caloric data as well as transport properties of pure fluids and multi-component mixtures. Solution method: Molecular dynamics, Monte-Carlo, various classical ensembles, grand equilibrium method, Green–Kubo formalism. Restrictions: No. The system size is user-defined. Typical problems addressed by ms2 can be solved by simulating systems containing typically 2000 molecules or less. Unusual features: Feature tools are available for creating input files, analyzing simulation results and visualizing molecular trajectories. Additional comments: Sample makefiles for multiple operation platforms are provided. Documentation is provided with the installation package and is available at http://www.ms-2.de. Running time: The running time of ms2 depends on the problem set, the system size and the number of processes used in the simulation. Running four processes on a “Nehalem” processor, simulations calculating VLE data take between two and twelve hours, calculating transport properties between six and 24 hours. [Copyright &y& Elsevier]

Abstract: A new automatic algorithm to calculate collision integrals from isotropic interaction potentials has been developed. The proposed method overcomes the limits of existing codes that need a priori definition of potential features. The algorithm efficiency has been tested by comparison with traditional approaches. The agreement achieved in reproducing published data is good. A theoretical analysis of the asymptotic behaviors, related to the accuracy of integral evaluation with respect to interval finiteness, is also reported. [Copyright &y& Elsevier]

Grain boundaries in ceramic barium titanate and related materials can be engineered in order to obtain desired transport behavior. Our ability to do so is closely related to kinetic limitations during the preparation. The close-packed structure of perovskites excludes native or foreign interstitials in the bulk. (Interstitial protons are regarded as OHO, using the Kröger-Vink notation). Antisites are also unlikely due to size, charge and coordination number mismatch. The possible point defects are, therefore, substitutionals and vacancies. The kinetic limitations of these species, and the results in terms of grain boundary engineering, are considered in this contribution. A clear distinction between three different conditions is made. At very high temperatures, it is assumed that all the relevant defects are mobile and can equilibrate, at least locally. Hence, their concentrations are all functions of the degrees of freedom of the system. At lower temperatures, the cation sublattice is frozen. Therefore, the concentrations of metal vacancies and substitutional cations are constants and, from local electrical neutrality point of view, a new parameter becomes important: the concentration of frozen charge. The concentrations of electronic defects and oxygen vacancies in this metastable state are functions of temperature, oxygen partial pressure and frozen charge. The normalized concentration of frozen metal vacancies is calculated as a function of the doping factor, f (defined as the ratio between the electron concentration at a given state and at a reference state), and a nonstoichiometry parameter. Around room temperature, the anion sublattice is also frozen, and only electrons and holes exhibit significant transport properties. [ABSTRACT FROM AUTHOR]•, using the Kröger-Vink notation). Antisites are also unlikely due to size, charge and coordination number mismatch. The possible point defects are, therefore, substitutionals and vacancies. The kinetic limitations of these species, and the results in terms of grain boundary engineering, are considered in this contribution. A clear distinction between three different conditions is made. At very high temperatures, it is assumed that all the relevant defects are mobile and can equilibrate, at least locally. Hence, their concentrations are all functions of the degrees of freedom of the system. At lower temperatures, the cation sublattice is frozen. Therefore, the concentrations of metal vacancies and substitutional cations are constants and, from local electrical neutrality point of view, a new parameter becomes important: the concentration of frozen charge. The concentrations of electronic defects and oxygen vacancies in this metastable state are functions of temperature, oxygen partial pressure and frozen charge. The normalized concentration of frozen metal vacancies is calculated as a function of the doping factor, f (defined as the ratio between the electron concentration at a given state and at a reference state), and a nonstoichiometry parameter. Around room temperature, the anion sublattice is also frozen, and only electrons and holes exhibit significant transport properties. [ABSTRACT FROM AUTHOR]

The dynamics of electrostatic potential barriers at grain boundaries (GBs) in Nb-doped SrTiO3 bicrystals is investigated using a unique combination of bulk and in-situ TEM electrical measurements across isolated GBs, coupled with electron holography under in-situ applied bias. The Nb bulk-doped bicrystals exhibit a positive GB potential that suppresses reversibly under applied bias greater than the nonlinearity threshold in the current-voltage curve. This suppression is interpreted as break-down of the potential barrier to current transport. The results on Nb bulk-doped bicrystals have been compared to those in which Mn has been added as a grain boundary specific dopant. This acceptor doping of the grain boundary causes an appreciable increase in the grain boundary resistance and extension of the nonlinear regime. A preliminary account of static electron holography shows a relatively flat potential profile across the GB, indicating probable compensation of donor states at the GB core with Mn-acceptors. Interestingly, the phase profile under applied bias in this case exhibits a reversible “dip” at the GB which is interpreted as an activation of GB trap states due to Mn-acceptor dopants trapping extra electrons (the majority charge carriers) at the GB core, inducing a negative GB potential, and diminishing current transport until the threshold bias is exceeded. The synergistic combination of nanoscale TEM measurements coupled with traditional macroscopic electrical measurements is emphasized. [ABSTRACT FROM AUTHOR]