A density functional (PBE, PBEsol, HSE06) study of the structural, electronic and optical properties of the ternary compounds AgAlX 2 (X = S, Se, Te)
TL;DR: In this paper, density functional theory (DFT) calculations for bulk structural, electronic and optical properties of ternary compounds AgAlX2 (X = S, Se, Te) were performed with two flavors of generalised gradient approximations (PBE and PBEsol) and the hybrid functional HSE06.
Abstract: First principles density functional theory (DFT) calculations for bulk structural, electronic and optical properties of ternary compounds AgAlX2 (X = S, Se, Te) were performed with two flavours of generalised gradient approximations (PBE and PBEsol) and the hybrid functional HSE06. Using cohesive energy as a stability criterion, we found that the chalcopyrite structure is the favoured phase for these materials. PBEsol gives structural properties closer to the experimental values when compared to the results of PBE. Tetragonal distortion and anion displacement were calculated and we found them to be the cause of the crystal field splitting. Reduction of the bandgap and band splitting around the Γ in the Brillouin zone was noted when spin-orbit coupling was included in our study especially in the case of AgAlTe2. The HSE06 bandgap and frequency dependent dielectric function were in very good agreement with experimental results. We have also shown that the maximum absorption peak lies in the ultraviolet range irrespective of the functional used. The refractive index is also discussed.
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TL;DR: This paper discusses the impact of three different computational databases based on density functional theory methods to the research community and provides recommendations on technical aspects of data reuse in the MGI.
Abstract: Materials innovations enable new technological capabilities and drive major societal advancements but have historically required long and costly development cycles. The Materials Genome Initiative (MGI) aims to greatly reduce this time and cost. In this paper, we focus on data reuse in the MGI and, in particular, discuss the impact of three different computational databases based on density functional theory methods to the research community. We also discuss and provide recommendations on technical aspects of data reuse, outline remaining fundamental challenges, and present an outlook on the future of MGI’s vision of data sharing.
118 citations
TL;DR: A new ambient-pressure metastable single-bonded 3D nitrogen allotrope (TrigN) of trigonal symmetry (space group R3[combining macron]) was calculated using density functional theory (DFT) and robust mechanical stability is revealed from the elastic constants calculation.
Abstract: A new ambient-pressure metastable single-bonded 3D nitrogen allotrope (TrigN) of trigonal symmetry (space group R) was calculated using density functional theory (DFT). A comprehensive characterization of this material, comprising thermodynamic, elastic, and spectral (vibrational, UV-vis absorption, and nuclear magnetic resonance) properties, was performed. Using high-throughput band structure calculation, the TrigN phase was characterized as an insulator with an indirect band gap of 2.977 eV. Phonon dispersion calculations justified that this structure is vibrationally stable at ambient pressure. The calculated Raman activities at the Γ-point demonstrated a rich pattern, whereas no relatively intense transitions were observed in its IR absorption spectrum. The TrigN material is almost transparent to visible light as well as to ultraviolet A and B. The main absorption peaks appeared within the range of 50–200 nm. The electron arrangement of the nitrogen nuclei in the studied nitrogen allotrope is much denser compared to that of the molecular nitrogen, which is in agreement with the calculated magnetic shielding tensor values. Robust mechanical stability is revealed from the elastic constants calculation. Due to strong anisotropy, the values of the Young's moduli vary from 281 to 786 GPa. A huge amount of internal energy is enclosed in the TrigN material. Upon decomposition to molecular nitrogen, the energy release is expected to be 11.01 kJ g−1 compared to the value of 10.22 kJ g−1 for the cubic gauche form of nitrogen. The TrigN allotrope possesses unique detonation characteristics with a detonation pressure of 146.06 GPa and velocity of 15.86 km s−1.
33 citations
TL;DR: An attempt was made to develop a general description of impact sensitivity, which is expected to be more easily convertible to the metal upon compression, to possess a spherical crystal habit and to have a greater number of electrons per atom as well as a high energy content and a low melting temperature.
Abstract: An attempt was made to develop a general description of impact sensitivity. For this purpose a set of 24 well-known, as well as recently synthesized, C–H–N–O–Cl explosives covering the wide range of impact sensitivity (h50 = 9–320 cm) was studied using first-principles calculations at different external pressures. To quantify impact sensitivity, a theoretical approach was developed based on the solid-state derived criteria, which include triggering pressure, average number of electrons per atom, crystal morphology, energy content and melting temperature. These criteria follow from the theoretical consideration of the crystal compression caused by an impact event. Apart of the compression, the influence of crystal habit shapes and energy content are also discussed. The main idea is in the electron flow probability from valence to conduction bands in a solid. To support the developed theoretical background, the corresponding numerical illustration is presented in the paper. The obtained empirical correlatio...
30 citations
TL;DR: In this article, the authors use hybrid density functional theory to screen four transparent conducting oxides (TCOs) for thermoelectric efficiency and analyse the limitations of TCOs as thermistors, showing that the dominant factor limiting these materials is the lattice thermal conductivity, and more specifically very long phonon mean free paths up to the order 10 μm.
Abstract: Thermoelectrics are a promising technology for converting heat into renewable electricity. Currently, however, most of the best thermoelectrics are based on toxic and/or rare materials such as PbTe and Bi2Te3, limiting their practical applications. Transparent conducting oxides (TCOs) are well understood and widely used commercially, so if they could be made into thermoelectrics, they could be rapidly and prolifically deployed. TCOs have been tested for their thermoelectric capabilities, however their performance is far below that needed for industrial deployment. Here we use hybrid density functional theory to screen four TCOs: BaSnO3, CdO, SnO2 and ZnO for thermoelectric efficiency and analyse the limitations of TCOs as thermoelectrics. We demonstrate that the dominant factor limiting these materials is the lattice thermal conductivity, and more specifically very long phonon mean free paths up to the order 10 μm, making them strong candidates for nanostructuring to increase performance. Based on these insights we critically discuss materials design principles for increasing the ZT of the conducting oxides.
20 citations
TL;DR: In this paper, the effect of non-metal dopants X (X=C, Si, N, P, S, Se, F, Cl, Br and I) with X@O and X@Ti on the geometric and electronic structures, stability, and photocatalytic property of perovskite BaTiO3 with wide band gap was investigated.
20 citations
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TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
146,533 citations
TL;DR: In this article, a semi-empirical exchange correlation functional with local spin density, gradient, and exact exchange terms was proposed. But this functional performed significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
Abstract: Despite the remarkable thermochemical accuracy of Kohn–Sham density‐functional theories with gradient corrections for exchange‐correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact‐exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange‐correlation functional containing local‐spin‐density, gradient, and exact‐exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first‐ and second‐row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
87,732 citations
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.
81,985 citations
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
57,691 citations
TL;DR: In this article, a method for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector is given, where the integration can be over the entire zone or over specified portions thereof.
Abstract: A method is given for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector. The integration can be over the entire Brillouin zone or over specified portions thereof. This method also has applications in spectral and density-of-state calculations. The relationships to the Chadi-Cohen and Gilat-Raubenheimer methods are indicated.
51,059 citations