China
Africa
Explore chapters and articles related to this topic
Theoretical Considerations of 2D Materials in Energy Applications
Published in Ram K. Gupta, 2D Nanomaterials, 2022
Harsha Rajagopalan, Sumit Dutta, Sourabh Barua, Pawan Kumar Dubey, Jyotsna Chaturvedi, Laxmi Narayan Tripathi
All the electronic structure calculations in this text are performed within the DFT framework, using the open-source code Quantum ESPRESSO.22,23 The code uses the Projector Augmented Wave method along with pseudopotentials. We use the PBE exchange-correlation functional for the calculations. The energy cut-off for the wavefunction has been set to 40 Ry and 80 Ry for bulk and monolayer calculation, respectively. The k-point mesh size is set to 9 × 9 × 9 for the bulk and 9 × 9 × 1 for the monolayer self-consistent (SCF) calculations. For the monolayer calculations, a supercell with a vacuum of 15 Å is used. The vacuum is required so that interactions between monolayers of repeating units are minimized otherwise this can lead to artefacts in the calculated properties.
Stability of X-IV-IV half Heusler semiconductor alloys: a DFT study
Published in Molecular Physics, 2021
The properties investigated in this work were achieved using the Quantum Espresso (QE) simulation package. The structural and electronic properties investigated were analyzed using the density functional theory (DFT). The hH semiconductors crystallize in the face-centred cubic structures belonging to the space group with space group number 216. Three possible Wyckoff positions were considered; ZYX, YZX, and XYZ, as reported in Table 1. The most stable and energetically favoured structure is the ZXY phase, as can be seen from Figure 1. The Ni atoms occupy Wyckoff position 4c (1/4, 1/4, 1/4), 4b (1/2,1/2, 1/2) is occupied by any of Si, Sn or Ge, while Hf occupies the 4a site (0, 0, 0). The remaining 4d (3/4, 3/4, 3/4) site is empty. In the ZXY phase, Ni is coordinated octahedrally in the position by the two other elements: HfSi, -HfSn or -HfGe, while Hf and X are tetrahedrally coordinated at and respectively. The crystal structure of the alloys was optimized by carrying out a fixed cell optimization relaxation calculation by applying the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm for the optimization of the ions with a possible shift in the x, y and z directions [54]. It is observed that there is an infinitesimal change in the atomic positions in the crystal structures studied.
Structural, electronic, magnetic, elastic and thermodynamic properties of Ni 4 N anti-perovskite
Published in Phase Transitions, 2021
A. Azouaoui, M. El haoua, I. El Hamdani, N. Benzakour, K. Haboubi, A. Hourmatallah, A. Rezzouk
In this work, we study the structural, electronic, magnetic, elastic and thermodynamic properties of using the density functional theory (DFT) implemented in Quantum ESPRESSO package. The obtained data from DFT calculations are used in Monte Carlo simulation with Ising model to study the thermal magnetization (M), magnetic susceptibility (χ) and calculate the critical exponents associated with χ and M and critical temperature ().
Autonomous synthesis system integrating theoretical, informatics, and experimental approaches for large-magnetic-anisotropy materials
Published in Science and Technology of Advanced Materials: Methods, 2022
Daigo Furuya, Takuya Miyashita, Yoshio Miura, Yuma Iwasaki, Masato Kotsugi
The electronic structures of the candidate materials were determined via first-principles calculations based on density functional theory (DFT) using Quantum Espresso (QE), a first-principles calculation package [28]. The MCA energy calculations were performed after structural relaxation to determine the mechanically stable structure for a given film configuration (Figure 1). Each unit cell had a tetragonal structure with the period of four layers. The results obtained herein for three known materials were compared with those of previous studies, and the Perdew-Becke-Ernzerhof (PBA) generalised gradient approximation (GGA) was applied as the exchange-correlation function for the structural relaxation, with a k-point of 12 × 12 × 8 [29]. Table 1 shows that the structural relaxation with the GGA for FeNi and CoNi is in good agreement with that for WIEN2K [30]. For FeCo, the B2 structure, rather than the L10 type, is the stable structure because it is the equilibrium state of the FeCo system (c/a = 0.707). The MCA energy was defined as the difference between the total energy when the magnetisation was oriented in-plane [100] and out-of-plane [001], and it was considered positive when the magnetisation easy axis was perpendicular to the plane. The results of appropriate exchange-correlation functions (GGA and local density function (LDA)) for MCA calculations are listed in Table 2 [31]. In Table 2, results from previous studies using all-electron calculation, SPR-KKR, WIEN2K, FP-LMTO, and two types of calculations using QE are presented [30,32]. GGA tends to underestimate the MCA energies, whereas calculations using QE LDA agree well with those in previous studies. In this study, we adopted LDA as the exchange-correlation function for MCA calculations with a k-point of 24 × 24 × 18. The tetrahedron method was used to efficiently perform the Brillouin zone integration [33]. The projector augmented wave (PAW) method was used to describe the core and valence electron potentials in these calculations [34]. The cut-off energy of the plane-wave basis was set to 75 Ry.