Computational materials physics

In order to search for a new anode material for lithium-ion batteries (LIBs), a borophene/boron nitride (B/BN) interface was investigated in detail using density functional theory. Borophene is an excellent two-dimensional (2D) anode material that offers high charging capacity and a low energy barrier, but it suffers from stability issues when it is used in its free-standing form. The findings of this work indicate that the thermal and mechanical stabilities of the borophene epilayer are notably increased by preparing its interface with a boron nitride substrate. The electronic properties of the lithiated and delithiated interface exhibited metallic behavior, whereas the mechanical stiffness of the interface increased three times when compared with that of the pristine borophene. The thermal stability was calculated by molecular dynamics and indicated a six times increase in its value for the interface. The interface exhibited a specific charging capacity of 1698 mA h g À1 , which is higher than that of bare borophene and several other 2D materials. Furthermore, nudged elastic band (NEB) calculations indicated a low energy barrier to diffusion of Li in the interface. These advantages of the B/BN interface make it an excellent choice as an anode material for LIBs.

We propose a long-range corrected hybrid meta-generalized-gradient approximation (GGA) functional, based on a global hybrid meta-GGA functional, M05 [Y. Zhao, N. E. Schultz, and D. G. Truhlar, J. Chem. Phys. 123, 161103 (2005)], and empirical atom-atom dispersion corrections. Our resulting functional, ωM05-D, is shown to be accurate for a very wide range of applications, such as thermochemistry, kinetics, noncovalent interactions, equilibrium geometries, frontier orbital energies, fundamental gaps, and excitation energies. In addition, we present three new databases, IP131 (131 ionization potentials), EA115 (115 electron affinities), and FG115 (115 fundamental gaps), consisting of experimental molecular geometries and accurate reference values, which will be useful in the assessment of the accuracy of density functional approximations.

In this work, we present ab-initio calculation results for the Tm3+ interstitial (), vacancy–interstitial complex (VGe-Tmi3+) and substitutional () defects in germanium (Ge) as determined by the density functional theory (DFT) using the Heyd, Scuseria, and Ernzerhof (HSE06) hybrid functional.............

We study here the magnetic properties of two dimensional silicene using spin polarized density functional theory. The magnetic properties were studied by introducingm onovacancy and di-vacancy, as well as by doping  phosphorous and aluminium into the pristine silicene. It is observed that there is no magnetism in the monovacancy system, while there is large significant magnetic moment present for the di-vacancy system. Besides, the numerical computation reveals that the magnitude of the magnetic moment is more when the system is doped with aluminium than phosphorous. All these theoretical predictions in this two dimensional system may shed light to open a new route to design silicon based nano-structures in spintronics.

Boron bulk crystals are marked by exceptional structural complexity and unusual related physical phenomena. Recent reports of hydrogenated α-tetragonal and a new δ-orthorhombic boron B 52 phase have raised many fundamental questions. Using density functional theory calculations it is shown that hydrogenated α-tetragonal boron has at least two stable stoichiometric compositions, B 51 H 7 and B 51 H 3. Thermodynamic modeling was used to qualitatively reproduce the two-step phase transition reported by Ekimov et al. [J. Mater. Res. 31, 2773 (2016)] upon annealing, which corresponds to successive transitions from B 51 H 7 to B 51 H 3 to pure B 52. The so obtained δ-orthorhombic boron is an ordered, low-temperature phase and α-tetragonal boron is a disordered, high-temperature phase of B 52. The two phases are connected by an order-disorder transition, that is associated with the migration of interstitial boron atoms. Atom migration is usually suppressed in strongly bound, covalent crystals. It is shown that the migration of boron atoms is likely to be assisted by the migration of hydrogen atoms upon annealing. These results are in excellent agreement with the above mentioned experiment and they represent an important step forward for the understanding of boron and hydrogenated boron crystals. They further open a new avenue to control or remove the intrinsic defects of covalently bound crystals by utilizing volatile, foreign atoms.

The dynamic spray-gun deposition method was developed in 2006 to fabricate Field Effect Transistors based on random arrays of carbon nanotubes (CNTFETs) for gas sensing applications. Thanks to this deposition method, we were able to fabricate hundreds of operational devices in a reproducible way that were integrated in electronic chips. Following this first implementation, we decided to widen the application of the deposition technique to the field of Energy and specifically to the fabrication of supercapacitors. In this context, we demonstrated in 2012 the fabrication of nanostructured electrodes for supercapacitors, using mixtures of graphene/graphite and carbon nanotubes (CNTs) increasing the device capacitance and the power delivered of a factor 2.5 compared to CNT based EDLC. Indeed, with high quality graphene we could reach a value of around 100W/Kg. This value is extremely promising also considering that it has been obtained with an industrially suitable technique. This dynamic spray-gun deposition has been also exploited for the fabrication of Resistance based Random Access Memories (ReRAM), making use of thin layers of graphene oxide (GO) and of oxidized carbon nanofibers (ox-CNFs). In the first case, 5000 cycles of "write" and

MAGNETIC SUSCEPTIBILITY AND MAGNETIZATION PLATEAUS IN Cd0.5Mn0.5Te DMS MATERIAL. In this paper, the magnetic susceptibilities and magnetization plateaus in Cd0.5Mn0.5Te DMS material are simulated in the spin exchange Heisenberg model using the Quantum Monte Carlo (QMC) method. The temperature dependence of the magnetic susceptibilities, (T) were simulated with inter-chain coupling parameter constant J1 = 12 and J2 = 4 with  = 0.2, 0.3, 0.4 and 0.5, respectively. In the mean time, magnetizations were simulated in the constant inter-chain coupling parameter J1 = 12 and J2 = 4 with  = 0.4 at temperatures of T= 0.50K, 0.25K, 0.10K and 0.05K in magnetic fields up to 60 T. The increase of the inter-chain coupling parameter J1 resulted decreasing and increasing the absolute values of (T) and TN, respectively. The magnetization simulations resulted no hysteresis was observed on increasing and decreasing the external magnetic field. The magnetization saturates at HS 55T. There are severa...

-The unique optical and electrical properties of indium tin oxide (ITO) films have been regarded as one of the prominent transparent and conducting oxides (TCO) films used as contact layer in several optoelectronic applications. ITO films optoelectronics properties were studied using a computer simulation method with respect to thickness. Developed mathematical models of ITO films optical and electrical properties were used to determine the trend features of the films with respect to thickness and wavelength. Improvement in optical transmission was observed as the films thickness decreases with film of low thickness exhibiting a maximum transmission of 91 % in the visible region. Electrical property improved with increasing thickness. Low electrical resistivity of 7.4 Ω-cm was obtained by film with small sheet resistance (10 Ω/sq). The remarkable features of the results suggest that the developed models are significant for understanding the trend features of ITO films optoelectronic properties.

Controlled excitation of materials can transiently induce changed or novel properties with many fundamental and technological implications. Especially, the concept of Floquet engineering, manipulation of the electronic structure via dressing with external lasers, has attracted some recent interest. Here we review the progress made in defining Floquet materials properties and give a special focus on their signatures in experimental observables as well as considering recent experiments realizing Floquet phases in solid state materials. We discuss how a wide range of experiments with non-equilibrium electronic structure can be viewed by employing Floquet theory as an analysis tool providing a different view of excitations in solids.

A structurally modified cathode material for Lithium ion battery is reported in this study. This study was based on first principle calculations to study the electronic, ionic, and diffusion properties of olivine phosphate family of cathode material. The attempt was made to modify the conventionally used cathode material LiFePO 4 by substituting Rare earth Gd on Fe sites. The Gd-4f's electrostatic interaction, exchange coupling, impact on lithium's intercalation, and ability to modify the crystal structure upon doping in the crystalline environment of the host have been studied and discussed in detail. The calculations on electronic structure, charge transfer between atoms, Li intercalation voltage, electron localization function (ELF) analysis, steric interaction between Li ion and metal cation (Fe and Gd) in both LiFePO 4 and LiGdPO 4 were carried out using prescribed methods. This trend of intercalation is related to structural relaxation in the vicinity of Gd which expedites the Li ion mobility without compromising the structural stability of the material. The analysis of interatomic steric interactions and ELF analysis helped to visualize the interactions in the cathode material. The findings of this study revealed that LiGdPO 4 could be a potential candidate for its use as cathode in lithium ion battery and relevant devices.

Graphene oxide (GO) is considered as a promising component for electronics because of its unique anisotropy, easy processing and sometimes claimed giant permittivity. The latter would arise from an enhanced electronic polarizability due to the presence of functional groups at the surface and edge of GO flakes. As a matter of fact, a number of publications have reported a very large permittivity of GO materials. Nevertheless, the reported values for the intrinsic relative permittivity vary significantly from a few units to several millions. Such variability raises a critical question on the actual and intrinsic permittivity of GO, and on difficulties of measurements due to the polarization of the electrodes. We presently report impedance spectroscopy characterizations of GO solutions with different solvents. We find very large capacitance at low frequencies, in agreement with previous reports. However, we also show that these results can be interpreted without considering the giant permittivity of GO. Actually, a simple equivalent circuit model allows us to confirm that GO does not have giant permittivity. We conclude that GO can be used as an electrolyte for supercapacitors or as a precursor for electrically conductive graphene-based materials, but not as an efficient additive to raise the permittivity of solvent or composites for electronics and energy storage applications.

We are investigating the use oflaw energy ions ( < 1 keY) in low temperature thin film growth techniques, ion beam deposition (IBD) and combined ion and molecular deposition (CIMD). In IBD, a thin film is directly grown from a low energy ion beam as the only source of material, while in CIMD, low temperature growth of thin films is achieved by depositing materials simultaneously from a low energy ion beam and one or several molecular beams. A simple model of the IBD process has been developed and accounts for atomic collisions and thermal diffusion during thin film growth. Computer simulation of IBD of Si on Si have been conducted as a function of ion energy to support more quantitatively this physical description orIED. The results show that the IBD growth mechanism is mediated by the fast diffusing interstitials and establish a low energy limit to achieve epitaxial growth by IBD that depends on the point defect diffusivities. The defect generation has to be confined in the subsurface region in order to favor interstitial recombination with the surface, leading to net thin film growth, and vacancy annihilation to prevent amorphization. The effect of point defect diffusivities on the lED growth process is also investigated. It is found that a model including fast moving interstitials can account for various experimental observations specific to IBD.

Monolayer tungsten disulfide (WS2) has recently attracted large interest as a promising material for advanced electronic and optoelectronic devices such as photodetectors, modulators, and sensors. Since these devices can be integrated in a silicon (Si) chip via back-end-of-line (BEOL) processes, the stability of monolayer WS2 in BEOL fabrication conditions should be studied. In this work, the thermal stability of monolayer single-crystal WS2 at typical BEOL conditions is investigated; namely (i) heating temperature of 300 °C, (ii) pressures in the medium-(10-3 mbar) and high-(10-8 mbar) vacuum range; (iii) heating times from 30 minutes to 20 hours. Structural, optical and chemical analyses of WS2 are performed via scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). It is found that monolayer single-crystal WS2 is intrinsically stable at these temperature and pressures, even after 20 hours of thermal treatment. The thermal stability of WS2 is also preserved after exposure to low-current electron beam (12 pA) or low-fluence laser (0.9 mJ/m 2), while higher laser fluencies cause photo-activated degradation upon thermal treatment. These results are instrumental to define fabrication and in-line monitoring procedures that allow the integration of WS2 in device fabrication flows without compromising the material quality.

The opening of a quantum confinement gap in nanostructured graphene yields extremely sensitive photodetectors, with electrical noise equivalent power lower than 10 −15 W Hz −0.5 at temperatures below 3 K, for detection of radiation in a very broad frequency range, including ultraviolet, visible and terahertz. Here we demonstrate the operation of these detectors in the presence of magnetic field as high as 7 T, paving the way to in situ spectroscopy of molecular nanomagnets.

The Novel Materials Discovery (NOMAD) Laboratory is a user-driven platform for sharing and exploiting computational materials science data. It accounts for the various aspects of data being a crucial raw material and most relevant to accelerate materials research and engineering. NOMAD, with the NOMAD Repository, and its code-independent and normalized form, the NOMAD Archive, comprises the worldwide largest data collection of this field. Based on its FAIR (findable accessible, interoperable, reusable) data infrastructure, various services are offered, comprising advanced visualization, the NOMAD Encyclopedia, and artificial-intelligence tools. The latter are realized in the NOMAD Analytics Toolkit. Prerequisite for all this is the NOMAD metadata, a unique and thorough description of the data, that are produced by all important computer codes of the community. Uploaded data are tagged by a persistent identifier (PID), and users can also request a DOI to make data citable. Developments and advancements of parsers and metadata are organized jointly with users and code developers. In this work, we review the NOMAD concept and implementation, highlight its orthogonality to and synergistic interplay with other data collections, and provide an outlook regarding ongoing and future developments. different skill sets, mastering physics, chemistry or materials science simulations with data analysis and management as well as hardware aspects. Also, to fully exploit the significant information and potential of the massive amounts of available data, requires to provide the community with proper infrastructures that allow for efficiently collecting, curating, and sharing data.

High-reflection interferential mirrors for current gravitational wave detectors (aLIGO, Advanced Virgo, KAGRA) are made of high-quality oxide multilayers deposited by ion beam sputtering (IBS) at the Laboratoire des Matériaux Avancés (LMA). For this task, LMA uses a large IBS custom-made machine (the grand coater GC) able to deposit very uniform coatings over very large surfaces, with diameter of some tens of cm. We report for the first time about the optical characterization by spectroscopic ellipsometry of oxide coatings deposited by the GC under strictly the same conditions used for the production of interferential mirrors. We have investigated oxide materials like silica (SiO 2), tantala (Ta 2 O 5) and titaniadoped tantala (Ti:Ta 2 O 5), providing for each material a broad-band (190-1700 nm) accurate determination of the complex index of refraction, with particular attention to wavelengths used in interferometers. Particular focus has been dedicated to the influence of Ti-doping on tantala coating. The doping induces a red-shift of the optical gap and an increase of the NIR refractive index. Furthermore, doping induces a decrease of the so-called Urbach energy, consistent with the well-known reduction of the internal friction in these kind of systems.

The high theoretical capacity of Li-O2 batteries attracts a lot of attention and this field has expanded significantly in the last two decades. In a more general way, the large number of articles being published daily makes it difficult for researchers to keep track of the progress in science. Here we develop a text mining program in an attempt to facilitate the process of reviewing the literature published in a scientific field and apply it to Li-O2 batteries. We analyze over 1,800 articles and use the text mining program to extract reported discharge capacities, for the first time, which allows us to show the clear progress made in recent years. In this paper, we focus on three main challenges of Li-O2 batteries, namely the stabilitycyclability, the low practical capacity and the rate capability. Indeed, according to our text mining program, articles dealing with these issues represent 86% of the literature published in the field. For each topic, we provide a bibliometric analysis of the literature before focusing on a few key articles which allow us to get insights into the physics and chemistry of such systems. We believe that text mining can help readers find breakthrough papers in a field (e.g. by identifying papers reporting much higher performances) and follow the developments made at the state of the art (e.g. by showing trends in the numbers of papers published -a decline in a given topic probably being the sign of limitations). With the progress of text mining algorithms in the future, the process of reviewing a scientific field is likely to become more and more automated, making it easier for researchers to get the "big picture" in an unfamiliar scientific field.