Spanish Initiative For Electronic Simulations With Thousands Of Atoms Research Articles

Orchestrating the impact of antisites and vacancy defects on the elastic and optoelectronic properties of boron arsenide.

Cubic boron arsenide (c-BAs), a semiconducting material with ultra-high thermal conductivity and carrier mobilities, has been studied using first-principles calculation. This study examined the elastic and optoelectronic properties of c-BAs. The challenge of subphase boron (B) formation in bulk form owing to the volatile nature of arsenic (As) makes it mandatory to calculate its optoelectronic properties, by producing vacancies and antisite defects with BAs (As atom on a B site) and AsB (B atom on an As site). The mechanical properties including bulk (B), shear (G) moduli, and Poison's ratio of all the systems were studied. It was found that mechanical instability of the structure is observed for the overall vacancy creation, arsenic substitution, and mutual antisite defects. Further, pristine c-BAs showed an indirect bandgap of 1.48eV. Defect formation reduces the bandgap and shifts the absorption peaks, which improves the overall optoelectronic properties of the host material. In addition, B vacancy formation shows the maximum optical absorption and reflectivity and low energy loss, suggesting its potential applications for optoelectronic devices. The obtained anticipated data from this study is for the optoelectronic and elastic properties of c-BAs, for the device applications in photonics and electronics. In this paper, the elastic and optoelectronic properties of the pristine and defected c-BAs were systematically investigated using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA). The SIESTA program uses pseudopotentials in the norm-conserving nonlocal forms and pseudo-atomic orbital (PAO) basis set with a double-zeta potential (DZP) which are fundamental for calculating the Hamiltonian and overlap matrices in O(N) operations.

Interface layer DFT study of first transition series XO oxides (X = Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn)

The whole universe is governed by energy in many forms. Solar cells use light energy and convert it into electrical energy. Nowadays, most of the applications depend on electrical activities. The interface layers are critical to the efficient and high-quality operation of solar cells. Solar cells, also known as photovoltaic devices, are a prospective choice for solar energy generation because of their compelling characteristics such as environmental friendliness, low cost, and lightweight [1]. We have explored new materials to design more efficient organic or inorganic solar cells through enhancement in structural and electronic properties. In this work, a Density Functional Theory (DFT) is implemented in the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA), which has been performed intending to explore the interface layer of solar cells. A theoretical study is conducted to explore the structural, electronic, magnetic and optical properties of eight different compounds of d-block oxide compounds. The first transition series of oxide compounds in 2-dimensional sheet arrangements, such as TiO, CrO, MnO, FeO, CoO, NiO, CuO, and ZnO, are explored in the fabrication of solar cells. In the magnetic properties, ZnO has 0 magnetic moments or spin polarization means there is equal number of spin-up and spin-down electrons are paired in each orbitals. However, the bandgap fluctuates from the properties of semiconductors to metals. Because the first transition series oxides exhibit essentially magnetic behaviour, they have two separate band gaps for spin-up and spin-down flucation, ranging from 0 to 1 eV and 0 to 4 eV, respectively. Among all the d-block transition series oxides, CoO has the highest optical qualities, with 4.7e+05 cm−1 absorption coefficient (α), 1.2e+05 S cm-1 conductivity (σ), and 0.125 reflectivity (ρ).

Electron-transport and gas sensing in armchair graphene nanoribbons by density functional method

Findings regarding the application of gas sensing on graphene based material have led to jump in nanotechnology. Hence, producing the high-efficiency materials in this technology is a priority. Recent development in graphene based material shows that it can be a good candidate for this tar-get. With this in mind, we theoretically studied the effect of different gas molecule absorption on armchair graphene nanoribbon. In order to identify, the electronic transport of armchair graphene nanoribbons AGNR (8) by using non-equilibrium Green’s function technique, the TRANSIESTA package was used. In order to study the geometry relaxation of device, Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) package was applied. Also, the generalized gradient approximation of Perdew, Burke and Ernzerhof (PBE) were chosen for the exchange correlation density function. For studying the gas sensing properties of AGNR numerical computations for CO, NO, CO2, and NH3gas molecules were adsorbed on the AGNR (8). Besides, the average local density of states (LDOS) and the transmission spectra T (E, V) for gas molecules adsorbed on the AGNR (8) were plotted. The current was measured as a function of the voltage of applied bias and the transmission spectra was investigated to see the effects of all configurations in the presence of gas molecules. Our results are encouraging and leading experimental research to develop high-quality graphene materials for well-organized applications base on gas sensing.

The effect of molecular twisting on electronic and transport properties of Chitosan: Ab initio approach

Abstract Chitosan is a linear chain copolymer composed of D-glucosamine and N-acetyl-D-glucosamine and is the second most naturally discovered polymer on the planet. In the research perspective, this material has non-toxicity, biocompatibility, and biodegradable in nature as in turn it has extraordinary applications in biomedical, food packaging, sensors and electronic gadgets [1] . In this study, a Density Functional Theory implemented in Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) has performed intending to determine the influence of the degree of rotation between the monomer of Chitosan. In each degree of rotation in the gape of 15 degrees, the changes in the structural, electronic and transport properties of chitosan dimer are investigated. Before the study of the effect of twisting in various properties the 2-monomer units of chitosan is optimized using conventional geometrical optimization techniques were comparatively analyzed for the total energies and other parameters. We supply the voltage of −4.0 to 4.0 V in each rotation and found the current in the interval with different rotation up to 0.15 μA. The bandgap is in the range of 0.1 eV to 4 eV in different degree of rotations.

First Principle Calculations of Effect of Hydrostatic Pressure on Ga0.75Cr0.25P

In this paper, the investigation of effect of hydrostatic pressure on the structural, electronic and magnetic properties of Ga0.75Cr0.25P ternary alloy in Zinc Blende (B3) phase at 0 GPa to 26 GPa pressure range has been done using first principle calculations as implemented in Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. The theoretical investigation of electronic and magnetic properties of this compound represents that the compound is half-metallic ferromagnet and show 100% spin polarization at different values of pressure. It is found that band gap increases with increase in pressure as spin polarized band structures experience changes with applied pressure. The calculated results show that lattice constant and volume of compound decrease along-with increase in induced local magnetic moments values on non-magnetic gallium and phosphorus atoms with applied pressure.

Study of structural, electronic, elastic and magnetic properties of Al0.75X0.25P (X=Cr, Mn, Fe) using Density Functional Theory

We have investigated the structural, electronic, elastic and magnetic properties of Al0.75X0.25P (X = Cr, Mn, Fe) Diluted Magnetic Semiconductors (DMS) in Zinc Blende phase (B3) using Density Functional Theory (DFT) as implemented in Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. The study of spin polarized electronic band structures and magnetic properties represent the induction of half metallic (HM) ferromagnetism with 100% spin polarisation in Al0.75Cr0.25P, Al0.75Mn0.25P and semiconductor (SC) behaviour of Al0.75Fe0.25P. Calculated positive values of phonon dispersion frequencies confirm the structural stability of compounds. The analysis of elastic properties of all materials predicts anisotropic and ductile nature.

DFT study of structural, electronic, elastic and magnetic properties of In0.75Cr0.25P

The theoretical calculations of structural, electronic, elastic and magnetic properties of In0.75Cr0.25P Diluted Magnetic Semiconductor (DMS) in Zinc Blende phase (B3) has been performed using Density Functional Theory (DFT) as implemented in the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code with LDA + U (U = 3) exchange–correlation (XC) potential. The study of spin polarized electronic band structures and magnetic properties represents the induction of half metallic ferromagnetic behaviour in In0.75Cr0.25P with 100% spin polarization. Different types of elastic parameters of ternary alloy have been calculated and results confirm that this compound is stable and predicts its anisotropic and ductile nature. The hybridization of Cr-3d states with s and p states of In and P develops some local magnetic moment on non magnetic In and P atoms. The calculated results of different properties are compared with available literature data and are in good agreement.

DFT Studies on Al Distribution and Bronsted Acid Sites in Zeolite ECR-1

Based on the density functional theory (DFT), the distribution of Al and Bronsted acid sites in zeolite ECR-1 were studied by utilization of SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) code at DZ2P basis set level. The 8 T cluster model was used to calculate the Al substitution energies at 10 independent T sites, the proton affinity energies and the adsorption energies of NH3 and acetone at the acid site were obtained. The results indicate that T1, T2 and T3 are the priority Al substitution sites in the skeleton of zeolite ECR-1, demonstrating that Al in MAZ and MOR layers of zeolite ECR-1 are rich and poor, respectively, which is consistent well with the experimental results. Bronsted acid is preferentially located in Al1(O8H)Si1, Al2(O12H)Si2 and Al3(O13H)Si3, and the most acidic site is Al3(O13H)Si3.

Study of effect of hydrostatic pressure on structural, electronic and magnetic properties of In0.75Mn0.25P using density functional theory

In this paper, the investigation of effect of hydrostatic pressure on the structural, electronic and magnetic properties of In0.75Mn0.25P Diluted Magnetic Semiconductor in Zinc Blende (B3) phase at 0 GPa–26 GPa pressure range is done using first principal calculations as implemented in Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code.The theoretical investigation of electronic and magnetic properties of this compound represents that the compound is half-metallic ferromagnet and show 100% spin polarization at different values of pressure. It is found that forbidden energy band gap increases with increase in pressure as spin polarized band structures experience changes with applied pressure. The calculated results show that lattice constant and volume of compound decreases along-with increase in induced local magnetic moments values of non-magnetic indium and phosphorus atoms with applied pressure.

PASTA: Python Algorithms for Searching Transition stAtes

Chemical reactions are often associated with an energy barrier along the reaction pathway which hinders the spontaneity of the reaction. Changing the energy barrier along the reaction pathway allows one to modulate the performance of a reaction. We present a module, Python Algorithms for Searching Transition stAtes (PASTA), to calculate the energy barrier and locate the transition state of a reaction efficiently. The module is written in python and can perform nudged elastic band, climbing image nudged elastic band and automated nudged elastic band calculations. These methods require the knowledge of the potential energy surface (and its gradient along some direction). This module is written such that it works in conjunction with density functional theory (DFT) codes to obtain this information. Presently it is interfaced with three well known DFT packages: Vienna Ab initio Simulation Package (VASP), Quantum Espresso and Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA). This module is easily extendable and can be interfaced with other DFT, force-field or empirical potential based codes. The uniqueness of the module lies in its user-friendliness. For users with limited computing resources, this module will be an effective tool as it allows to perform the calculations image by image. On the other hand, users with plentiful computing resources (such as users in a high performance computing environment) can perform the calculations for large number of images simultaneously. This module gives users complete flexibility, thereby enabling them to perform calculations on large systems making the best use of the available resources. Program summaryProgram Title: PASTAProgram files doi:http://dx.doi.org/10.17632/rv7fdm5gkf.1Licensing provisions: BSD 3-clauseProgramming language: PythonExternal routines/libraries: numpy, matplotlibNature of problem: Most of the reactions have an energy barrier on their reaction pathway. This energy barrier affects the progress of the reaction.Solution method: We implement the NEB, CI-NEB and AutoNEB method to locate transition state and estimate the energy barrier. Our module works with density functional theory codes: VASP, SIESTA and Quantum Espresso presently.

LDA + U Study of Induced Half Metallicity in Cr-Doped GaN

Half-metallic ferromagnetism in the Ga1 − xCrxN compound at different concentrations, x = 25, 12.5 and 6.25 %, have been investigated using density functional theory as implemented in code Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) using LDA + U as exchange-correlation (XC) potential, to find out the possibility of new diluted DMSs. The outcomes reveal that transition metal atom (Cr) doping in GaN induces ferromagnetism. The 3d levels of the TM ion originate a half-metallic gap at the Fermi level in the majority spin channel for all concentrations. Moreover, diluted magnetic semiconductor compounds retain the half-metallic nature at all concentrations, i.e., x = 0.25, 0.125 and 0.0625, with 100 % spin polarization at the Fermi level (EF). The total magnetic moment of these compounds is due to Cr-3d states, and the existence of a small magnetic moment on Ga and N, non-magnetic atoms, for all doping concentrations is a consequence of p-d hybridization of Cr-d and N-p states. The calculated values of s-d exchange constant N α and p-d exchange constant N βconfirm the ferromagnetic character of the Cr-doped GaN compound.

Electronic Properties of 6H Hexagonal SrMnO3

SrMnO3 ceramic was prepared by conventional high-temperature sintering method. Dielectric studies were performed within the temperature range 125–300 K at the frequency 10–400 kHz. The electronic properties of stoichiometric and oxygen defected SrMnO3 crystal in hexagonal 6H- P63/mmc symmetry at 0 K were calculated in ab initio procedure based on density functional theory using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. The lattice parameters and density of states were obtained. The ideal 6H-SrMnO3 crystal has the band gap energy about 0.2–0.3 eV at 0 K. Contribution of an exchange-correlation energy into the total energy is about 32%, a magnetic moment about 3 µB.

Effect of Dopant Concentration on Electronic and Magnetic Properties of Transition Metal-Doped ZrO2

Electronic and magnetic properties of the bulk monoclinic phase of pure and doped zirconia (ZrO2) are calculated. Calculations have been performed using density functional theory based Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. We have considered substitutional doping of transition metals (TM) V, Cr, Mn and Fe in zirconia corresponding to concentrations ranging from 3.125 to 25 %. Our results show that Cr, Mn-, and Fe doped oxides are half-metallic and the half-metallicity remains intact on reducing the dopant concentrations. The total magnetic moment is mainly due to d states of TM atoms and small induced magnetic moment exists on other nonmagnetic atoms as well. Also as the oxygen vacancy influences the performance of oxidebased devices, therefore we model the influence of oxygen vacancy on the magnetic moments in pure and doped zirconia. Our results show that pure oxide system remains nonmagnetic even on the introduction of oxygen vacancy whereas magnetic moment values for TM doped oxide changes. In the presence of oxygen vacancy, the total magnetic moment of V-, Cr-, and Mn doped cell increases whereas it decreases for Fe doping. This shows that oxygen vacancy (V O) has a strong influence on the magnetic properties of the doped oxides. The results may be useful for further study on TM doped ZrO2 system.

FT-Raman and FTIR spectra of photoactive aminobenzazole derivatives in the solid state: A combined experimental and theoretical study

This study reports the experimental investigation of two photoactive aminobenzazole derivatives in the solid state by FT-Raman and Infrared Spectroscopies (FTIR) and its comparison with theoretical models. The optimized molecular structure, vibrational frequencies, and corresponding vibrational assignments of these compounds have been investigated experimentally and theoretically using Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) and Gaussian03 Software Package. The FT-Raman and FTIR spectra were acquired with high resolution and emission frequencies identified by simulating the vibrational modes. The most intense peak observed in the FT-Raman spectra is the in-plane deformation vibrational of O–H bond that could be related to the vibrational region responsible for the stabilization of the enol conformer in the ground state which undergoes ESIPT to form a keto tautomer in the excited state. Additionally, the position of the amino group played an important role on the vibrational characteristics of the studied compounds. Also, the simulations proved to be a good approach in undertaking the FTIR and FT-Raman experiments. The use of graphic correlations helps us to determine the method and basis that best fit the experimental results.

<i>Ab Initio</i> Study of the Electronic and Vibrational Properties of 1-nm-Diameter Single-Walled Nanotubes

The electronic structure, band gap, density of states of the (8,8), (14,0) and (12,3) single-walled carbon nanotubes by the SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) method in the framework density-functional theory (DFT) with the generalized gradients approximation (GGA) were studied. Also, we studied the vibrational properties of the (8,8) and (14,0) nanotubes. Only the calculated relaxed geometry for (12,3) nanotube show significant deviations from the ideal rolled graphene sheet configuration. The electronic transition energies of van Hove singularities were studied and compared with previous results. The calculated band structures, density of states and dispersion curves for all tubes were in good agreement with theoretical and experimental results.

Interactions Between Amino Acid‐Tagged Naphthalenediimide and Single Walled Carbon Nanotubes for the Design and Construction of New Bioimaging Probes

AbstractA new synthetic route to functionalized single walled carbon nanotubes (SWNTs) via supramolecular interactions using a specifically designed naphthalenediimide (NDI) nanoreceptor is demonstrated. The tendency of the NDI to spontaneously form composites with carbon nanomaterials leads to fluorescent amino acid tagged SWNTs, which are dispersible in widely accessible organic solvents (CHCl3, DMSO) as well as in biocompatible cell medium (EMEM, Eagle's modified essential medium). The X‐ray crystal structure of the first iodine‐tagged and amino acid‐functionalized NDI molecule, designed especially to facilitate the high resolution transmission electron microscopy (HR TEM) imaging whilst retaining its ability to self‐assemble into a nanodimensional receptor in weakly polar solvents, is also described. A new hybrid material, NDI@SWNT, was prepared and characterized as dispersed in organic solvents and aqueous media and in the solid state by HR TEM, tapping mode atomic force microscopy (TM AFM), scanning electron microscopy (SEM), circular dichroism, Raman and fluorescence spectroscopies (steady‐state single and two‐photon techniques). Combined microscopy techniques, density functional theory (DFT) calculations using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) program and spectroscopic measurements in solution indicate that amino acid‐functionalized NDI interacts strongly with SWNTs and forms a donor‐acceptor complex. Density functional theory (DFT) calculations predicted the geometry and the binding energies of an NDI molecule loaded onto a SWNT strand and the possibility of charge transfer interactions within the hybrid. The NDI@SWNT composite translocates into cells (e.g. FEK‐4, HeLa, MCF‐7) as an intact object and localizes in the cells' cytoplasm and partially in the nucleus. The NDI coating enhances the biocompatibility of SWNTs and mediates its intracellular localization as shown by confocal fluorescence imaging and fluorescence lifetime imaging (FLIM) techniques. The excited state fluorescence lifetime of the probes in cells versus solution phase indicates that the probes remain unaffected by the change in their chemical environment within the experimental timescale (2 h).

Theoretical investigations of the experimentally observed selectivity of a cobalt imprinted polymer

A cobalt imprinted polymer synthesised, for reducing the volume of radioactive waste generated during nuclear reactor decontaminations, using vinylbenzyl iminodiacetate (VbIDA) as the functional ligand, has been found to be selective for cobaltous ions over excess ferrous ions. The selectivity of the polymer has been investigated through theoretical calculation of the formation energies of complexes involved by using the ab-initio density functional theory (DFT) code SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms). The formation energies of complexes of Fe 2+, Co 2+, Cu 2+ and Ni 2+ with the free functional ligands as well as with ligands attached to the crosslinkers have been calculated. The calculations revealed that the ferrous forms an unstable complex with the ligands attached to the crosslinkers. The formation energy calculation results were found to corroborate the experimentally observed selectivity order.

All-electron and pseudopotential study of the spin-polarization of the V(001) surface: LDA versus GGA

The spin-polarization at the V(001) surface has been studied by using different local [local spin-density approximation (LSDA)] and semilocal [generalized gradient approximation (GGA]) approximations to the exchange-correlation potential of DFT within two ab initio methods: the all-electron tight-binding linear muffin-tin orbital atomic-sphere approximation and the pseudopotential linear combination of atomic orbitals code SIESTA (Spanish initiative for electronic simulations with thousands of atoms). A comparative analysis is performed first for the bulk and then for a N-layer V(001) film $(7<~N<~15).$ The LSDA approximation leads to a nonmagnetic V(001) surface with both theoretical models in agreement (disagreement) with magneto-optical Kerr (electron-capture spectroscopy) experiments. The GGA within the pseudopotential method needs thicker slabs than the LSDA to yield zero moment at the central layer, giving a high surface magnetization (1.70 Bohr magnetons), in contrast with the nonmagnetic solution obtained by means of the all-electron code.