Vienna Ab Initio Simulation Package Research Articles

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

The First Principle Study of <i>β</i>-CuAgSe Subcells

CuAgSe has been considered as a promising thermoelectric material because of its high mobility and low thermal conductivity. The superior performance of CuAgSe is closely related to its crystal structure and electric properties. In this work, the stabilities and electronic structures of different three CuAgSe subcells have been theoretically investigated using Vienna Ab initio Simulation Package (VASP) with DFT calculations. We found that the different occupations of copper atoms would affect the stability and electronic structures of CuAgSe subcells. The various directions of Cu-Se chain in neighbor layers will result in different stabilities and electronic properties.

Structural Optimization and the Study of the Electronic, Mechanical, Thermodynamic and Phonon Properties of Mg2sn from First Principle

First principles pseudopotential method based on density functional theory is used to investigate the Structural, Mechanical, Phonon, Thermodynamic and Electronic properties of Mg2Sn. The equilibrium properties including lattice constant, bulk modulus, pressure derivative cohesive energy, young modulus, shear modulus were determined. The results obtained were compared with available experimental and other available results. Mg2Sn was found to be brittle in nature with a non-metallic properties as shown by the value of the Cauchy pressure of -4.03. The Phonon dispersion curve of Mg2Sn was obtained utilizing the PBE-GGA exchange-correlation potential as employed in the Vienna Ab-Initio Simulation Package (VASP) computer code. The gap separating the acoustic and the optical branch of the curve was found to be about 50cm-1 at X-point. The thermodynamic properties of the material was investigated in the temperature of 0-800K. At room temperature, the calculated value of the specific heat capacity ( ) is 71.28J/mol which is in good agreement with experimental and other results. Mg2Sn was found to a narrow gap semiconductor with an indirect bandgap of magnitude of 0.175eV.

Irvsp: To obtain irreducible representations of electronic states in the VASP

We present an open-source program irvsp, to compute irreducible representations of electronic states for all 230 space groups with an interface to the Vienna ab-initio Simulation Package. This code is fed with plane-wave-based wavefunctions (e.g. WAVECAR) and space group operators (listed in OUTCAR), which are generated by the VASP package. This program computes the traces of matrix presentations and determines the corresponding irreducible representations for all energy bands and all the k-points in the three-dimensional Brillouin zone. It also works with spin–orbit coupling (SOC), i.e., for double groups. It is in particular useful to analyze energy bands, their connectivities, and band topology, after the establishment of the theory of topological quantum chemistry. Accordingly, the associated library – irrep_bcs.a – is developed, which can be easily linked to by other ab-initio packages. In addition, the program has been extended to orthogonal tight-binding (TB) Hamiltonians, e.g. electronic or phononic TB Hamiltonians. A sister program ir2tb is presented as well. Program summaryProgram title: irvspCPC Library link to program files:https://doi.org/10.17632/y9ds5nnm2f.1Licensing provisions: GNU Lesser General Public LicenseProgramming language: Fortran 90/77Nature of problem: Determining irreducible representations for all energy bands and all the k-points in 230 space groups. It is in particular useful to analyze energy bands, their connectivities, and band topology.Solution method: By computing the traces of matrix presentations of space group operators for the eigen-wavefunctions at a certain k-point in a given space group, one can determine irreducible representations for them.

Ab initio study of oxygen vacancy effects on structural, electronic and thermoelectric behavior of AZr1-xMxO3 (A = Ba, Ca, Sr; M= Al, Cu, x = 0.25) for application of memory devices

The structural, electronic and thermoelectric properties of AZr1-xMxO3 (A = Ba, Ca, Sr; M = Al, Cu, x = 0.25) without and with an oxygen vacancy (Vo) have been unveiled using the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA) functional along with Tran-Blaha modified Becke-Jonhson (TB-mBJ)approximation based on Density Functional Theory (DFT) in the framework of WIEN2k code for memristors applications. Moreover, isosurface charge density plots have been calculated by using Vienna ab initio Simulation Package (VASP) simulation code. The analysis of structural parameters reveals that substituting Zr4+ with Al3+ and Cu2+ causes the lattice distortion which tends to increase in the presence of Vo along with dopant. The study of band structure, density of states (DOS) and isosurface charge density plots predict the enhanced charge conduction and formation of conducting filaments (CFs) for all composites with dopant and/or Vo. Moreover, spin polarized density of states for Cu doped composites has also been calculated to confirm the large exchange splitting of Cu-3d states. The thermoelectric characteristics of considered composites have also been explored using the Boltztrap code to better explain the semi-classical Boltzmann transport theory. Thermoelectric parameters confirm the semiconductor nature of all composites, ensuring the compatibility for memristors and thermoelectric devices applications. In addition to this spin polarized thermoelectric behavior of Cu doped composites that ensure the contribution of spin down (↓) states of Cu for charge transport mechanism. The SrZrCuO3+Vo composite is found most promising candidate followed by BaZrCuO3 for memristors applications while, CaZrCuO3 is found most suitable amongst studied composites for thermoelectric devices.

Oxygen Vacancies Altering the Trapping in the Proton Conduction Landscape of Doped Barium Zirconate

Acceptor-doped barium zirconate is one of the most promising proton conducting materials for stationary hydrogen fuel cells. Dopant-defect proton traps shape the proton conduction landscape. Inspired by findings that oxygen vacancies may decrease trapping near some dopant defects ( Chem. Mater. 2018, 30, 4919−4925), the effect of oxygen vacancies on the proton conduction landscape of barium zirconate is explored at 12.5% doping with aluminum, scandium, and yttrium dopant at the zirconium site. Density functional theory (DFT) with the PBE functional in the Vienna ab initio simulation package (VASP) was used to find the electronic energy for barium zirconate configurations. The conjugate-gradient minimization method is used to find the lowest energy structures and the climbing nudged elastic band (cNEB) method is used to find transition states. As the dopant (D) ion radius increases, the lattice size expands from 4.24 to 4.29 Å and increases DO6 octahedral tilting in barium zirconate. Inclusion of an oxygen vacancy broadens ZrOD and ZrOZr angle distributions. While there are three distinct minima for oxygen vacancy locations, relative energies of minima and transition states show that only the dopant nearest neighbor oxygen vacancy is significant for aluminum- and scandium-doped barium zirconate. In contrast, the yttrium-doped system shows 67% and 33% probabilities at 800 K for the dopant nearest and second nearest neighbor oxygen vacancies, respectively. The dopant nearest oxygen vacancy leaves the dopant polyhedral center charge exposed. The small size of the aluminum dopant allows oxygen ions to shift and partially screen the dopant charge. This coupled with strong hydrogen bonds increases proton trapping. For the larger scandium and yttrium ions, there is no significant oxygen ion rearrangement around the dopant with a nearest neighbor oxygen vacancy. Instead, the positive dopant charge exposed by the vacancy raises the energy of several dopant nearest neighbor proton sites decreasing trapping locally.

Machine Learning in Computational Surface Science and Catalysis: Case Studies on Water and Metal-Oxide Interfaces.

The goal of many computational physicists and chemists is the ability to bridge the gap between atomistic length scales of about a few multiples of an Ångström (Å), i. e., 10−10 m, and meso- or macroscopic length scales by virtue of simulations. The same applies to timescales. Machine learning techniques appear to bring this goal into reach. This work applies the recently published on-the-fly machine-learned force field techniques using a variant of the Gaussian approximation potentials combined with Bayesian regression and molecular dynamics as efficiently implemented in the Vienna ab initio simulation package, VASP. The generation of these force fields follows active-learning schemes. We apply these force fields to simple oxides such as MgO and more complex reducible oxides such as iron oxide, examine their generalizability, and further increase complexity by studying water adsorption on these metal oxide surfaces. We successfully examined surface properties of pristine and reconstructed MgO and Fe3O4 surfaces. However, the accurate description of water–oxide interfaces by machine-learned force fields, especially for iron oxides, remains a field offering plenty of research opportunities.

First Principles Prediction of Corrosion Kinetics As a Function of Microstructural Features in Precipitation Hardened Aluminum Alloys

In this poster, first principles density functional theory (DFT) implemented in the Vienna Ab Initio Simulation Package (VASP)1 is coupled with micro-kinetic model2 to simulate the electrochemical corrosion kinetics of some commonly identified intermetallic particles3 (IMPs) associated with precipitation hardened aluminum alloys such as AA7075. First principles DFT calculation is used to characterize the adsorption energies for the cathodic reaction intermediates on intermetallic surfaces. The species include atomic oxygen (O) and hydroxide (OH) as intermediates for the oxygen reduction reaction. We will show that when coupling the thermodynamic calculations with an appropriate micro-kinetic model, we can predict the corrosion kinetics of IMPs. One of the most desirable properties obtained from the simulated polarization curve is the corrosion potential of the IMPs. The corrosion potential can indicate the relative nobilities of IMPs with respect to the alloy matrix. Experimentally the corrosion potential of IMPs on the range of microns are measured via a micro-capillary cell technique. With the state of the art TEM, localized corrosion even down to the nm scale can be characterized4. On the simulation side, however, a method that can be directly compared to experimental data has not yet been fully realized. Attempts to estimate corrosion potentials from the surface work functions obtained by DFT calculations have been made in recent literature but the direct correlation of work function to the corrosion potential has a significant band of uncertainty associated with it. Rather than finding direct correlation, we incorporate work function into the kinetics equation as one of the input parameters. Our simulated for Al7FeCu2, one of the most commonly identified IMP in high strength aluminum alloy, is -337 mVNHE, which is in good agreement with experimental data (-307 mVNHE). We contend here that a first-principles model founded in electrode kinetics is a promising path forward for bridging first-principles simulation and experiment in corrosion science.Reference G. Kresse and J. Furthmüller, Comput. Mater. Sci., 6, 15–50 (1996).H. A. Hansen, V. Viswanathan, and J. K. Nørskov, J. Phys. Chem. C, 118, 6706–6718 (2014) http://pubs.acs.org/doi/abs/10.1021/jp4100608.N. Birbilis and R. G. Buchheit, J. Electrochem. Soc., 152, B140 (2005) http://jes.ecsdl.org/cgi/doi/10.1149/1.1869984.Y. Zhu et al., Acta Mater., 189 (2020).

(Invited) Beneficial Role of Interstitial Carbon on Corrosion Resistance of Carbon Steels

Martensitic carbon steels with fine grains are used as important industrial materials. Interstitial carbon atoms are located in the octahedral sites in the body-centered tetragonal (bct) crystal structure, and bring high strength to martensite. Although it has been reported that the interstitial carbon has the beneficial effect on the corrosion resistance of steels,1,2 the role of interstitial carbon is still unclear. In this research, first-principles calculations were applied to explore the role of interstitial carbon on the corrosion resistance of martensite.The specimens were martensitic carbon steels with three carbon contents: 0.001 mass%, 0.44 mass%, and 0.88 mass% C. The specimens were heat-treated at 1223 K and then, quenched in water to form martensitic structure. Potentiodynamic polarization of the specimens was conducted using 1 M H2SO4. In addition to the electrochemical measurements, the first-principles calculations based on density functional theory (DFT) were carried out. For the calculation, the Vienna Ab initio Simulation Package (VASP) was used with the projector augmented wave (PAW) method 3 and GGA-PBE potential for both of the bulk and surface phases of martensite. The bct-based supercells are adopted and the interstitial carbon atoms were located at the octahedral sites in bct crystal structures.In the potentiodynamic polarization curves of the martensitic specimens in 1M H2SO4, the current densities of all specimens increased continuously with the electrode potential. This indicates that the specimen surfaces dissolved actively and were not passivated in this solution. The active dissolution current decreased with increasing in carbon content, suggesting that the active dissolution of martensite was suppressed by the interstitial carbon.By using the first-principles calculations, the effect of interstitial carbon atoms on the electronic structure of bct iron (martensite) was investigated. It was clarified that the electronic density of states (DOS) of iron atoms at and near the Fermi level decreased by increasing carbon concentration. Considering that the valence electrons near and at the Fermi level are responsible for the electrochemical reactivity (reduction/oxidation reactivity), this is evidence that interstitial carbon enhances the electrochemical stability of bct iron. Also, the effect of interstitial carbon on the work function of bct iron was investigated by the first-principles calculations. The work function on bct (110) and bct (100) surfaces increased with increasing interstitial carbon content, which might result in the suppression of the active dissolution of martensite.References; M. Kadowaki, I. Muto, Y. Sugawara, T. Doi, K. Kawano, and N. Hara, J. Electrochem. Soc., 164, C962 (2017).M. Kadowaki, I. Muto, Y. Sugawara, T. Doi, K. Kawano, and N. Hara, J. Electrochem. Soc., 165, C711 (2018).G. Kresse and J. Furthmüller, Phys. Rev. B, 54, 11169 (1996).

Influence of Additional Doping of Divalent Ions on Emission Intensity of Mn-Doped CaAl12O19

In recent years, phosphor-converted white light-emitting diodes (pc-WLED) have great attention due to long lifetime and low power consumption compared to traditional lighting source. The most popular method to fabricate the pc-WLEDs is a combination of blue LED chips (GaN) and yellow phosphor (Y3Al5O12:Ce3+), which shows high luminescence intensity. However, such pc-WLED does not have high color rendering property due to the lack of red color emission component. In order to solve the problem and obtain warmer colored pc-WLEDs, it is efficient to incorporate a red phosphor in the pc-WLED. It is known that Mn-doped phosphor have been studied because of their broad excitation band in UV-blue region and their deep red emission. Among the oxide basis phosphors, several materials such as Mn-doped CaAl12O19 [1] and Mg2TiO4 [2] were reported with good luminescence property. To increase the emission efficiency, additional doping into such Mn-doped oxide phosphors were examined. The remarkable enhancement of the emission intensity was reported for Mg co-doping in Mn-doped CaAl12O19 [3]. However, the mechanism why such enhancement was achieved by co-doping has not yet been fully understood. In this study, influence of additional doping of divalent ions, such as Mg2+, Zn2+ and Cd2+, on the red-emission intensity of Mn-doped CaAl12O19 is investigated. All the samples were synthesized with conventional solid-state reaction method by changing divalent ions concentration. Crystal structure of the synthesized samples was characterized with the powder X-ray diffraction (XRD) technique. To determine the charge state and the local environment of Mn ions, the Electron Spin Resonance (ESR) spectra were observed.The observed photoluminescence spectra of non-doped and Cd2+, Mg2+, Zn2+ co-doped CaAl12O19:Mn are shown in Fig. 1. In all cases, it is shown that divalent ions dopings could enhance the emission intensity, among which Mg2+ doping shows the largest enhancement. In the observed ESR spectra of non-doped and Cd2+, Mg2+, Zn2+ co-doped CaAl12O19:Mn, six peaks derived from hyper fine structure of Mn4+ could be seen in all the samples. It is noted that Mg and Zn co-doping significantly affects the spectral profiles, whereas only slight change was observed in Cd co-doped one. This indicates that Mg and Zn co-doping influence on local structure of Mn. In order to understand the effect of divalent ions doping on the enhancement of the red emission intensity, the first principles calculations within a density functional theory (DFT) have been also performed. As it is well known that the local environment of Mn ions is quite important on the emission intensity, local environment of Mn ions in CaAl12O19 were examined by substituting Mn ions at five crystallographically independent Al sites using the Vienna Ab initio Simulation Package (VASP)[4]. Using the same method, influence of additional dopings of divalent ions are investigated. In the conventional DFT calculations with local density approximation (LDA) or generalized gradient approximation (GGA) the band gap is always underestimated. As there are some methods developed recently to obtain more accurate band gap, for the electronic structure analysis, the modified Becke-Johnson potential by Tran and Blaha (TB-mBJ) [5] implemented in WIEN2k package [6] was employed here. In addition, Hubbard U correction on the d electron state is adopted to represent the strong correlation between d-electrons on Mn ions, which cannot be fully included in TB-mBJ.AcknowledgementThis work was partially supported by the Joint Research Center for Environmentally Conscious Technologies in Materials Science (project No. 30009, 30012, 31008, and 31017) at ZAIKEN, Waseda University.

Electrochemical Performance of Nickel Silicide Electrodes for Lithium-Ion Batteries in an Ionic-Liquid Electrolyte

Developing lithium-ion batteries (LIBs) with a high energy density, long cycle, and high safety is essential for establishing a sustainable society because LIBs are used as electric vehicle batteries and stationary batteries for utilizing renewables. Silicon (Si) has great potential as an anode active material for next-generation LIBs due to its high theoretical capacity (3580 mA h g- 1 for Li15Si4). However, Si electrodes show poor cycle stability, which is mainly caused by a large volume change in Si during the lithiation (charge) and delithiation (discharge) reactions. Additionally, Si has other disadvantages, such as high electrical resistivity and a low Li+ diffusion coefficient. We have previously investigated the lithiation and delithiation properties of pure binary silicide (M ySiz, M : transition metal) electrodes. Some electrodes maintained a high reversible capacity in an ionic-liquid electrolyte, whereas they showed a poor cycling performance in a conventional organic-liquid electrolyte. In contrast, the effect of difference in crystal phase of silicides composed of the same elements on the lithiation and delithiation properties has not yet been clarified. Herein, we synthesized various pure nickel silicide (Ni-Si) powders. and investigated their lithiation and delithiation properties in an ionic-liquid electrolyte. Ni-Si powders (NiSi2, NiSi, Ni2Si, and Ni3Si) were synthesized by a mechanical alloying (MA) method. The obtained powders were characterized by X-ray diffraction (XRD) and Raman spectroscopy. XRD patterns were identified compared with patterns in the Inorganic Crystal Structure Database (ICSD). Each silicide electrode was prepared by a gas deposition (GD) method, which does not require a binder or conductive agent. We assembled 2032-type coin cells, which consisted of the silicide electrode as the working electrode, Li metal foil as the counter electrode and a glass fiber filter as the separator. 1 mol dm- 3 (M) lithium bis(fluorosulfonyl)amide (LiFSA) in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)amide (Py13-FSA) was used as an ionic-liquid electrolyte. A galvanostatic charge-discharge test was carried out in the potential range between 0.005 and 2.000 V vs. Li+/Li at 303 K. The current density was set at 50 mA g- 1. To discuss the charge density of each element in Li x Ni y Si z , a first-principle calculation based on density functional theory (DFT) was performed using the projector augmented wave (PAW) method as implemented in the plane wave code of the Vienna Ab initio Simulation Package (VASP). A generalized gradient approximation (GGA) was used as the term exchange correlation with a kinetic cutoff of 350 eV. Brillouin zone sampling was performed with an 8×8×8 k point mesh within a Gamma point centered mesh scheme. We synthesized various Ni-Si powders by a MA method. Comparing the XRD pattern of the prepared samples and the corresponding ICSD pattern, all peaks were assigned to pure Ni-Si phase. Additionally, there were no peaks arising from the raw materials (Ni and Si). In Raman spectra, peaks assigned to crystalline Si (c-Si) and amorphous Si (a-Si) appear at approximately 520 and 490 cm- 1, respectively. Each silicide also gives no Raman peaks of c-Si and/or a-Si which indicates that neither c-Si nor a-Si is included in the synthesized powders. Therefore, the MA treatment successfully produced a pure Ni-Si phase. Fig.1 shows the dependence of the gravimetric discharge capacity of various nickel silicide electrodes on the cycle number in 1 M LiFSA/Py13-FSA.The NiSi2 electrode exhibited the highest initial capacity of approximately 800 mA h g- 1, and the Ni3Si electrode showed the second highest capacity. The results demonstrated that there was no correlation between initial capacity and silicon content in Ni-Si. To reveal the difference in the initial capacity, we determined the charge density of each element in Li x Ni y Si z based on computational chemistry. Li and Si have positive charges in all silicides, whereas Ni has a negative charge in Li x Ni y Si z . These results indicate that Li has a high affinity with Ni in Li x Ni y Si z . In addition, it is suggested that the higher the affinity of Ni with Li is, the higher the initial capacity is. Furthermore, we investigated the distance between Li and close atoms (Ni or Si) in Li x Ni y Si z . The initial capacity increased with an increase in the distance. Therefore, both the affinity of Ni with Li and the distance between Li and neighboring atom should influence on the initial capacity. Figure 1

Experimental and Theoretical Analysis of Photoluminescence from Mn-Doped Oxide Phosphors

Most of the current phosphor materials are prepared by doping dilute amount of rare-earth or transition metal ions, which act as emission center, in matrix materials. Among such phosphors, rare-earth doped oxides show good properties such as high luminescence and high stability for long term use, etc. However, due to the limitation of the rare-earth elements in the earth, rare-earth free phosphor materials have been strongly demanding, and therefore such materials have been extensively investigated these years. Although there are wide varieties of dopants for such rare-earth free phosphors, Mn4+ doped phosphor materials, which show red emission, are one of the most attractive materials. In order to design new phosphors doped with Mn ions, it is essential to know the local environment of the doped Mn ions in an atomic scale and the electronic structures of Mn-doped materials. Although the local environment analysis is mandatory, such analysis is very difficult for dilute dopants. In the current study, local environment analysis of Mn ions doped in some oxides were carried out by using the X-ray absorption near edge structure (XANES) measurements and the electronic structure calculations for such materials have been performed with the first principles calculations.All the samples were fabricated with the conventional solid-state reaction method changing the concentration of Mn ions and/or matrix oxides, such as CaTiO3, CaZrO3, CaSnO3, CaAl12O19, Mg2TiO4 and so on. Crystal structures of the synthesized materials were characterized with powder X-ray diffraction technique. Mn K- and L- XANES spectra were observed at BL9C of KEK-PF in the transmission mode and BL4B in UVSOR in total electron yield mode, respectively. Theoretical XANES spectra to be compared with the experimental ones were prepared with the WIEN2k package [1]. Prior to the detailed electronic structure calculations, geometry optimizations were carried out computationally to investigate the local environment of the doped Mn ions in the matrix oxides by the first principles calculations within a density functional theory level using the Vienna Ab-initio Simulation Package, VASP [2]. The electronic structures of the Mn-doped materials after above geometry optimizations were investigated with modified Becke-Johnson potential [3], which was recently developed electron-electron correlation functional and implemented in WIEN2k package is accurate for the band-gap estimation of the wide variety of semiconductors.AcknowledgementThis work was partially supported by the Joint Research Center for Environmentally Conscious Technologies in Materials Science (project No. 30009, 30012, 31008, and 31017) at ZAIKEN, Waseda University.

Effect of Cobalt Content on Charge Compensation Mechanism of LiNixMnyCozO2 Cathode for Lithium Ion Battery

LiCoO2 (LCO) is commonly used as a cathode for Li-ion batteries (LiBs) owing to its excellent intercalation nature, high voltage, and cyclic performance [1, 2]. However, LCO has issues due to the potential risk of future price increases of Co [3, 4]. Many efforts have been made to reduce the amount of Co in the cathode by replacing it with Ni and/or Mn, and LiNixMnyCozO2 (NMC) has been developed. NMC622, which contains 60 mol % of Ni in the transition metal composition, is now adopted in the majority of the electric vehicle battery chemistry. Although Ni-rich NMC is a promising alternative to low-Co cathodes, it is not clear whether the amount of Co can be further reduced from the present NMC622 without degrading cyclic stability. To further reduce the amount of Co, it is necessary to clarify the role of Co in the charge compensation mechanism and replace it with alternative elements with functions similar to those of Co.In this study, we conducted XAFS, XRD and first-principles calculations for the NMC cathode with various transition metal composition ratios to clarify that the roles of Co, Ni, Mn, and O in the charge compensation mechanism. Synchrotron X-ray experiments were performed at SPring-8 and NewSUBARU synchrotron radiation facility in Japan. The first-principles calculations were carried out with Vienna Ab-initio Simulation Package (VASP) [5, 6], which uses plane-wave basis sets.Fig. 1 shows the oxygen K-edge XANES spectra collected by the partial fluorescence yield (PFY) method at different states of charge (SOCs). As for the LCO, the peak intensity around 528 eV changed along with the SOC, suggesting that oxygen contributes to the charge compensation. Similar spectral changes were also observed with NMC111, NMC622, and slightly with NMC 811. In contrast, the white line energy in the Co L3-edge absorption hardly changed at any transition metal composition. Although there are various theories about the role of Co and oxygen in the charge compensation [7], our results show that there is no obvious change in the charge state of Co and oxygen contributes the most to the charge compensation in the LCO system. Detailed analysis including first-principles calculations will be discussed at the meeting.[1] K. Mizushima et al., Mater. Res. Bull. 15, 783 (1980).[2] A. Du Pasquier et al., J. Power Sources 115, 171 (2003).[3] P.A. Nelson et al., Modeling the Performance and Cost of Lithium-Ion Batteries for Electric-Drive Vehicles, Argonne National Laboratory, 2012.[4] Elsa A. Olivetti e t al., Joule 1, 229 (2017).[5] P. E. Blöch, Phys. Rev. B 50, 17953 (1994).[6] G. Kresse et al., Phys. Rev. B 59, 1758 (1999).[7] B. Li et al., Adv. Mater. 29, 1701054 (2017) Figure 1

AMMCR: Ab initio model for mobility and conductivity calculation by using Rode Algorithm

We present a module to calculate the mobility and conductivity of semiconducting materials using Rode’s algorithm. This module uses a variety of electronic structure inputs derived from the Density Functional Theory (DFT). We have demonstrated good agreement with experimental results for the case of Cadmium Sulfide (CdS). We also provide a comparison with the widely used method, the so-called relaxation time approximation (RTA) and demonstrated a favorable improvement of the results compared to RTA. The present version of the module is interfaced with the Vienna ab initio simulation package (VASP). Program summaryProgram title:AMMCRCPC Library link to program files:https://doi.org/10.17632/x4yjz735xz.1Developer’s repository link:https://ikst.res.in/research/download-centerLicensing provisions: BSD 3-clauseProgramming language: C++Nature of problem: Long-range interactions between electrons and longitudinal optical (LO) phonons are a major challenge in computing transport in polar semiconductors. Due to such LO phonons or generally polar optical phonons (POP), electron phonon scattering requires special attention since they cannot be studied using a simple framework such as relaxation time approximation (RTA).Solution method: We have developed a code that calculates mobility and conductivity by using ab initio inputs with the Rode algorithm, which treats the interaction between the polar optical phonons and electrons in a proper way.

TransOpt. A code to solve electrical transport properties of semiconductors in constant electron–phonon coupling approximation

A Fortran code, TransOpt (formerly named Transoptic) is presented. This code calculates electrical transport coefficients of semiconductor materials based on Boltzmann transport theory in the relaxation time approach with the recently developed constant electron–phonon coupling approximation. The code interfaces with the Vienna ab initio Simulation Package (VASP). The band structure related scattering phase space is calculated and used in determining the effective carrier relaxation time. The electronic structure part of the relaxation time is treated explicitly with using the detailed first-principles, while the electron–phonon coupling matrix (EPCM) part is treated as a constant. This constant EPCM can be parameterized using the deformation potential method in semiconductors, and the absolute value of electrical conductivity can thus be obtained. The code can also use full electron–phonon data from Quantum Espresso. Transport properties, including the electrical conductivity, the Seebeck coefficient, electronic thermal conductivity, Lorenz number, power factor, and electronic fitness function, can be calculated by TransOpt. The electron group velocities vnk as a function of the position in the Brillouin zone, k, can be determined in two different ways: 1) The momentum matrix method, which naturally avoids the “band crossing” problem, and yields better convergence with the number of first-principles k points and 2) the gradient method, where vnk is solved by the gradient in reciprocal space of the dispersion relation, which avoids the need to compute momentum matrix. Several examples are presented to highlight the major features of TransOpt.

Comparison of the effects of Sr2+ and Ca2+ substitution on the structural and electronic properties of the perovskites CH3NH3Pb1-xYxI3 (Y[dbnd]Sr, Ca) by using the Density Functional Theory

The Vienna ab-initio simulation package (VASP) and Density Functional Theory (DFT) calculation method are used to study the structural and detailed electronic properties through atomic substitution in the CH3NH3Pb(1-x)Y(x)I3 (YSr, Ca x = 0.125, 0.25, 0.50, 0.75, and 1.0) perovskites. We determined that the non-stoichiometric crystal structures were calculated as a distorted orthorhombic phase as predicted by the tolerance factor range 0.7 < t < 0.9. The bandgaps of the stoichiometric CH3NH3SrI3 and CH3NH3CaI3 compounds are calculated 3.261 eV (Q → Γ indirect) and 3.144 eV (Q → Γ indirect), respectively and they are very high for ideal photo absorbers. We were determined that the bandgap (Γ → Γ direct) of the CH3NH3Pb0.875Ca0.125I3, CH3NH3Pb0.750Ca0.250I3, and CH3NH3Pb0.875Sr0.125I3 compounds are calculated 1.44 eV, 1.54 eV, and 1.525 eV respectively and are more suitable for ideal photo absorbers. It was seen that Ca2+ substitution was more successful than Sr2+ substitution.

Structure and enhanced dielectric temperature stability of BaTiO3-based ceramics by Ca ion B site-doping

Capacitor is an important part of many electronic devices, so the temperature stability as one key parameter of capacitor needs to be improved constantly for meeting the requirements of various application temperature. Here, combined with the X-ray diffraction (XRD), selected area electron diffraction (SAED) and Vienna Ab-initio Simulation Package (VASP) calculation, it was confirmed that Ca ion can substitute the Ti site in the BaTi1-xCaxO3-x [BTC100×] (0 ≤ x ≤ 0.05) ceramics synthesized by solid-phase method which greatly improved the low-temperature stability of dielectric constant. Moreover, introducing Bi3+ and Zn2+ into BTC4 to form (1-y)BaTi0·96Ca0·04O2.96-yBi(Zn0·5Ti0.5)O3 [(1-y)BTC4-yBZT] (0.1 ≤ y ≤ 0.2) ceramics can further improve the dielectric-temperature stability by means of diffused phase transition and core-shell structure. Most importantly, the 0.85BTC4-0.15BZT ceramics with a pseudocubic perovskite structure possessed a temperature coefficient of capacitance at 25 °C (TCC25°C) being less than ±15% over a wide temperature range of −55 °C–200 °C and a temperate dielectric constant (ε = 1060) and low dielectric loss (tanδ = 1.5%), which measure up to the higher standard in the current capacitor industry such as X9R requirements.

Positive/Negative Phototropism: Controllable Molecular Actuators with Different Bending Behavior

Herein, a series of molecular actuators based on the crystals of (E)-2-(4-fluorostyryl)benzo[d]oxazole (BOAF4), (E)-2-(2,4-difluorostyryl)benzo[d]oxazole (BOAF24), (E)-2-(4-fluorostyryl)benzo[d]thi...

Surface alloying of chromium/tungsten/stannum on pure nickel and theoretical analysis of strengthening mechanism

Surface alloying of chromium/tungsten/stannum on pure nickel were facilitated by high current pulsed electron beam (HCPEB) irradiation. The evolution of microstructure and microhardness of the irradiated surface were characterized. On the other hand, first-principles calculations, based on density functional theory (DFT), implemented in the Vienna Ab initio Simulation Package (VASP), were adopted to compute and simulate the solid solution mechanism of alloy element doping in matrix. From the simulation, the Sn atom resulted in the largest increase of lattice constant due to its largest atomic radius among three elements, and which Sn doping caused the strongest inter atomic force. Therefore, the VASP simulation indicated that Ni-Sn HCPEB irradiated sample has the highest hardness value among three different irradiated samples, which is good agreement with the experimental results obtained.

Qvasp: A flexible toolkit for VASP users in materials simulations

We have developed a flexible toolkit, named qvasp (quickly use vienna ab-initio simulation package), to assist users to prepare input files and process output files for Vienna Ab-initio Simulation Package (VASP) during materials simulations. Here, we systematically introduced its design architecture and techniques, as well as how to use qvasp to save time and energy during the materials calculations. This program offers a user-friendly Linux-based command-line interface and aims to help users perform various materials simulations through VASP on high performance computing platform, such as structure optimization, single point energy, work function, electronic structure simulations, mechanical and optical property calculations. In particular, this toolkit provides the basic functions to roll up nanotube from nanosheet and cleave surface from bulk, it also provides an interface for users to customize their own workbags (such as constructing heterojunction structure). All features are designed user-friendly, elegantly and efficiently. We believe this toolkit will be helpful for the users in the field of computational materials science. Program summaryProgram title: qvaspCPC Library link to program files:http://dx.doi.org/10.17632/2v4m39dt3n.1Licensing provisions: MIT License.Programming language: Fortran95+BashNature of problem: In the material simulation process, there is a lack of flexible, free and user-customizable pre- and post-processing toolkit for Vienna Ab-initio Simulation Package (VASP).Solution method: A Linux-based command-line toolkit was developed to assist VASP users to perform various types of calculations, such as structure optimization, single point energy, work function, electronic structure simulations, mechanical and optical property calculations. It also provides an interface for users to customize their own tool packages. The elegant and user-friendly command line interface makes it as a core set of toolkits with a wide range of applicability in materials simulations.