We present an implementation of G0W0 calculations including spin–orbit coupling (SOC) enabling investigations of large systems, with thousands of electrons, and we discuss results for molecules, solids, and nanocrystals. Using a newly developed set of molecules with heavy elements (called GW-SOC81), we find that, when based upon hybrid density functional calculations, fully relativistic (FR) and scalar-relativistic (SR) G0W0 calculations of vertical ionization potentials both yield excellent performance compared to experiment, with errors below 1.9%. We demonstrate that while SR calculations have higher random errors, FR calculations systematically underestimate the VIP by 0.1 to 0.2 eV. We further verify that SOC effects may be well approximated at the FR density functional level and then added to SR G0W0 results for a broad class of systems. We also address the use of different root-finding algorithms for the G0W0 quasiparticle equation and the significant influence of including d electrons in the valen...

Implementation and Validation of Fully Relativistic GW Calculations: Spin–Orbit Coupling in Molecules, Nanocrystals, and Solids

PbMoO4 micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120 °C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet−visible (UV−vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra confirmed that the PbMoO4 micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnecte...

http://www.nanotecnologia.com.br/redecmdmc/lab/arquivos_publicacoes/2987_Morphology%20and%20Blue%20Photoluminescence%20Emission.pdf

Morphology and Blue Photoluminescence Emission of PbMoO4 Processed in Conventional Hydrothermal

β-Rhombohedral Boron: At the Crossroads of the Chemistry of Boron and the Physics of Frustration

Recent scientific advances on organic-inorganic hybrid perovskites are mainly focused on the improvement of power conversion efficiency. So far, how compression tunes their electronic and structural properties remains less understood. By combining in situ photocurrent, impedance spectroscopy, and X-ray diffraction (XRD) measurements, we have studied the electrical transport and structural properties of compressed CH3NH3PbI3 (MAPbI3) nanorods. The visible light response of MAPbI3 remains robust below 3 GPa while it is suppressed when it becomes amorphous. Pressure-induced electrical transport properties of MAPbI3 including resistance, relaxation frequency, and relative permittivity have been investigated under pressure up to 8.5 GPa by in situ impedance spectroscopy measurements. These results indicate that the discontinuous changes of these physical parameters occur around the structural phase transition pressure. The XRD studies of MAPbI3 under high pressure up to 20.9 GPa show that a phase transformation below 0.7 GPa, could be attributed to the tilting and distortion of PbI6 octahedra. And pressure-induced amorphization is reversible at a low density amorphous state but irreversible at a relatively higher density state. Furthermore, the MAPbI3 nanorods crush into nanopieces around 0.9 GPa which helps us to explain why the mixed phase of tetragonal and orthorhombic was observed at 0.5 GPa. The pressure modulated changes of electrical transport and visible light response properties open up a new approach for exploring CH3NH3PbI3-based photo-electronic applications.

Visible light response, electrical transport, and amorphization in compressed organolead iodine perovskites

Most of the group IV, III-V, and II-VI compounds crystallize in semiconductor structures under ambient conditions. Upon application of pressure, they undergo structural phase transitions to more closely packed structures, sometimes metallic phases. We have performed density functional calculations using projector augmented wave (PAW) pseudopotentials to determine the transition pressures for these transitions within the local density approximation (LDA), the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), and the strongly constrained and appropriately normed (SCAN) meta-GGA. LDA underestimates the transition pressure for most of the studied materials. PBE under- or overestimates in many cases. SCAN typically corrects the errors of LDA and PBE for the transition pressure. The accuracy of SCAN is comparable to that of computationally expensive methods like the hybrid functional HSE06, the random phase approximation (RPA), and quantum Monte Carlo (QMC), in cases where calculations with these methods have been reported, but at a more modest computational cost. The improvement from LDA to PBE to SCAN is especially clearcut and dramatic for covalent semiconductor-metal transitions, as for Si and Ge, where it reflects the increasing relative stabilization of the covalent semiconducting phases under increasing functional sophistication.

https://link.aps.org/accepted/10.1103/PhysRevB.97.094111

Accurate critical pressures for structural phase transitions of group IV, III-V, and II-VI compounds from the SCAN density functional

We report on an original method that measures sample thickness in a diamond anvil cell under high pressures. The method is based on two hypotheses: completely plastic deformation on the gasket and completely elastic deformation of the diamonds. This method can further eliminate the effect of diamond deformation on the thickness measurement of a sample, which permits us to measure the thickness of alumina up to 41.4 GPa.

Thickness measurement of sample in diamond anvil cell.

The effect of grain boundary on electrical transportation properties is a basic physical problem and also a subject of material science and technology. In situ electrical measurement of powdered materials under high pressure provides a chance to figure out the electrical properties of grain boundaries. In this letter, the authors report an in situ impedance spectroscopy method used in conjunction with a diamond anvil cell for electrical property research of grain boundaries under high pressure. Powdered CdS was pressed up to 23GPa and an impedance arc corresponding to the grain boundary was detected. It was found that the electrical property of the grain boundary changed with pressure and could be determined by the resistance and the relaxation frequency. Pressure decreases the effective scattering section of the grain boundary to charge carriers, and finally leads to the decrease of resistance and activation energy of the grain boundary.

In situ electrical impedance spectroscopy under high pressure on diamond anvil cell

We report an alumina-encapsulated microcircuit on a diamond anvil for high-pressure and high-temperature electrical conductivity measurement. An alumina thin film was deposited on a diamond anvil as a thermal insulation layer for laser heating, on which a molybdenum film was deposited and photolithographically fabricated to a van der Pauw circuit. The introduction of the alumina layer significantly improves the laser heating performance. This specially fabricated diamond anvil permits us to measure the resistivity of (Mg0.875Fe0.125)2SiO4 at 3450K and 35GPa in a laser-heated diamond anvil cell. We expect to substantially extend the pressure-temperature scale of in situ resistivity measurement.

New diamond anvil cell system for in situ resistance measurement under extreme conditions

High-pressure Raman spectra and in situ electrical resistivity measurement of the dumbbell-like ZnO microcrystals have been investigated by using the diamond-anvil-cell technique at room temperature. The dumbbell-like ZnO microcrystals were synthesized via a facile solution method under mild conditions. In terms of the Raman results, the dumbbell-like ZnO microcrystals underwent a transition from wurtzite to rock-salt structure with increasing pressure and the phase-transition pressure was about 11.13 GPa. In situ electrical resistivity measurement of the dumbbell-like ZnO microcrystals was performed on a designed diamond anvil cell. The change in electrical resistivity related to the phase structure for the ZnO microcrystals was observed with the applied pressure of up to 34.86 GPa. Moreover, the pressure dependence of the electrical resistivity for the dumbbell-like ZnO microcrystals annealed at different conditions was also investigated.

Phase transformation and resistivity of dumbbell-like ZnO microcrystals under high pressure

Using finite element analysis, the authors studied the steady current field distribution under the configuration of van der Pauw method [L. J. van der Pauw, Philips Tech. Rev. 20, 220 (1958)] for resistivity measurement in a diamond anvil cell. Based on the theoretical analysis, the authors obtained the theoretical accuracy curve of the van der Pauw method. This method provides accurate determination of sample resistivity when the ratio of sample thickness to its diameter is less than 0.45. They found that the contact area between electrode and sample is a key factor in the resistivity measurement accuracy and its size is dependent on the sample diameter for a given measurement accuracy.

Dongmei Zhang

Papers

Thickness measurement of sample in diamond anvil cell.

In situ electrical impedance spectroscopy under high pressure on diamond anvil cell

New diamond anvil cell system for in situ resistance measurement under extreme conditions

Phase transformation and resistivity of dumbbell-like ZnO microcrystals under high pressure

Finite element analysis of resistivity measurement with van der Pauw method in a diamond anvil cell