The density functional theory (DFT) + U method is adopted to study the electronic structure, magnetism, chemical bonding, and thermodynamic properties of USiO4. A bandgap of 3.1 eV is obtained by analyzing the band diagram of USiO4. The calculated structural parameters are consistent with the recent experimental results. The charge density and charge density differences are studied in order to analyze the chemical bonds in USiO4. The results indicate that interactions within USiO4 are mostly ionic and exhibit weak covalent character. In addition, phonon behavior is studied in detail. We predict phonon frequencies and assign and analyze the Raman-active and infrared-active modes at the Γ point. Furthermore, thermodynamic properties such as the internal energy ΔE, Helmholtz free energy ΔF, constant-volume specific heat CV, and entropy S are investigated in the region between 0 K and 1000 K. The results are expected to provide useful information for subsequent experiments on USiO4.
The single-crystal lithium hydride (LiH) generally grows in a gradient temperature region with the Bridgman method. A stable and appropriate temperature gradient is crucial in the crystallization process. In this paper, the temperature variation of single-crystal LiH growth is calculated by the finite element method (FEM). It is shown that the LiH compact melted entirely after heating to 750 °C at 10 °C/min in a dual-temperature furnace and holding for 2.4 h. The crystallization margin was 46.5 °C after holding for 5 h. The crystallization margin of LiH at the cone point, respectively, decreased to 33.7 °C, 28.6 °C, 25.6 °C, and 16.5 °C when the upper furnace was maintained at 750 °C, and lower furnace was cooled to 680 °C, 650 °C, 630 °C, and 550 °C, respectively. The optimal conditions for obtaining large size and high-quality LiH single crystals were predicted to be 630 °C at a lower-temperature-zone, 200 mL/min (cooling water flux), and 20 mm/h rise rate of the furnace. Based on the parameters of the above simulation, we synthesized LiH single crystal. X-ray diffraction (XRD) patterns showed that the LiH single crystal exhibited a (2 0 0) crystallographic plane at 44.5° with good chemical stability in air.
The electronic structure and spectroscopic properties of GeCl+ are studied by high-level ab initio calculations by considering spin–orbit coupling (SOC). The potential energy curves (PECs) and spectroscopic constants of 12 Λ–S states and 23 Ω states are calculated using the multi-reference configuration interaction plus Davidson correction method (MRCI + Q), which are in good agreement with the experiment. Based on the calculated SO matrix and the PECs of the Ω states, the interaction between the d3Π state and other states caused by the SOC and the double-potential well structure caused by the avoided crossing rule and the properties of transitions d3Π0+–X1Σ+ 0+, d3Π1–X1Σ+ 0+, and a3Σ+ 1–X1Σ+ 0+ are studied. Our results indicate that the previously observed spectra of GeCl+ in the 290–325 nm range should be assigned as the a3Σ+ 1–X1Σ+ 0+ transition. Moreover, the predissociation behavior of the d3Π state between the vibrational levels v′ = 1 and v′ = 10 is discussed, and the radiative lifetimes of transitions d3Π0+–X1Σ+ 0+ and d3Π1–X1Σ+ 0+ are evaluated on the order of microseconds, while a3Σ+ 1–X1Σ+ 0+ is on the order of milliseconds. We estimate that the strongest bands of a3Σ+ 1–X1Σ+ 0+ are the 0–16, 0–17, and 0–18 bands. This study will promote our understanding of the detailed electronic structure and spectra of the GeCl+ radical cation.
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