Pressure-induced metallization in the absence of a structural transition in the layered transition-metal dichalcogenide ZrSe2.

First-principles calculations were carried out on the ZrSe2 compound, which has been of interest owing to its technologically important physical properties. The structural, electronic and optical properties of this compound were investigated under pressure through the plane wave pseudopotential approach within the framework of density functional theory. A comparison between the computed crystal structure parameters and the corresponding experimental counterparts shows a very good agreement between them. Fitting the pressure-volume data using the third-order Birch-Murnaghan equation of state yielded a bulk modulus B0 = 38.17 GPa and a pressure derivative of bulk modulus B'0 = 8.2 for hexagonal ZrSe2. The relationship between the band structure and pressure is revealed. We calculated the total density of state (TDOS) under different pressures and partial density of state (PDOS) from 0 to 10 GPa. According to our calculations, metallization of hexagonal ZrSe2 is predicted to occur at around 10 GPa and pressure-induced band-gap engineering reveals the transformation of the indirect to direct band gap with increasing pressure. Furthermore, optical properties, such as the complex dielectric function, refractive index and reflectivity spectra of this compound, were studied for incident electromagnetic waves in an energy range up to 45 eV. The contributions to various transition peaks in the optical spectra are analyzed and discussed with the help of the energy-dependent imaginary part of the dielectric function.

Total-factor energy efficiency of ten major global energy-consuming countries.

Improving energy efficiency is regarded as a key path to tackling global warming and achieving the Sustainable Development Goals (SDGs). In 2020, the energy consumption of the world's ten major energy-consuming countries accounted for 66.8% of the global total. This paper applied data envelopment analysis (DEA) to calculate these ten major energy-consuming countries' total-factor energy efficiency (TFEE) at national and sectoral levels from 2001-2020, and explored the influencing factors of total-factor energy efficiency with the Tobit regression model. The results showed significant difference in the ten countries' energy efficiency. The United States and Germany topped the list for total-factor energy efficiency, while China and India were at the bottom. Meanwhile, the energy efficiency of the industrial subsector has increased significantly over the past two decades, while that of the other subsectors has been relatively flat. The industrial structure upgrading, per capita GDP, energy consumption structure, and foreign direct investment had significant impacts on energy efficiency with national heterogeneity. Energy consumption structure and GDP per capita were determinative factors of energy efficiency.

Carbon flow through continental-scale ground logistics transportation.

The flourishing logistics in both developed and emerging economies leads to huge greenhouse gas (GHG) emissions; however, the emission fluxes are poorly constrained. Here, we constructed a spatial network of logistic GHG emissions based on multisource big data at continental scale. GHG emissions related to logistics transportation reached 112.14 Mt CO2-equivalents (CO2e), with seven major urban agglomerations contributing 63% of the total emissions. Regions with short transport distances and well-developed road infrastructure had relatively high emission efficiency. Underlying value flow of the commodities is accompanied by logistics carbon flow along the supply chain. The main driving factors affecting GHG emissions are driving speed and gross domestic product. It may mitigate GHG emissions by 27.50-1162.75 Mt CO2e in 15 years if a variety of energy combinations or the appropriate driving speed (65-70 km/h) is adopted. The estimations are of great significance to make integrated management policies for the global logistics sector.