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G. M. Dongho Nguimdo

Bio: G. M. Dongho Nguimdo is an academic researcher from University of the Witwatersrand. The author has contributed to research in topics: Phase transition & Density functional theory. The author has an hindex of 2, co-authored 2 publications receiving 35 citations.

Papers
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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.

40 citations

Journal ArticleDOI
TL;DR: In this article, the structural, dynamical, mechanical stability and electronic properties of the ternary AgInS2 compounds under pressure were investigated using ab initio density functional theory techniques.
Abstract: We employ state-of-the-art ab initio density functional theory techniques to investigate the structural, dynamical, mechanical stability and electronic properties of the ternary AgInS2 compounds under pressure. Using cohesive energy and enthalpy, we found that from the six potential phases explored, the chalcopyrite and the orthorhombic structures were very competitive as zero pressure phases. A pressure-induced phase transition occurs around 1.78 GPa from the low pressure chalcopyrite phase to a rhombohedral RH-AgInS2 phase. The pressure phase transition around 1.78 GPa is accompanied by notable changes in the volume and bulk modulus. The calculations of the phonon dispersions and elastic constants at different pressures showed that the chalcopyrite and the orthorhombic structures remained stable at all the selected pressure (0, 1.78 and 2.5 GPa), where detailed calculations were performed, while the rhombohedral structure is only stable from the transition pressure 1.78 GPa. Pressure effect on the bandgap is minimal due to the small range of pressure considered in this study. The meta-GGA MBJ functional predicts bandgaps which are in good agreement with available experimental values.

9 citations


Cited by
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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

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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

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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

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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

Journal ArticleDOI
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