Cu-Au intermetallic alloys are classic paradigms in the history of alloy theory for studying order-disorder transition, phase stability, and so on. However, density functional theory with a generalized gradient approximation (GGA) fails to describe their formation energies and Au-rich ground states, e.g., calculated formation energies are nearly 40% smaller than experimental values. In this work, we found that these discrepancies, which are also common in other Cu-transition metal (TM) intermetallic alloys, are actually caused by the fact that GGA produces Cu-3d bands with a shallower energy level than the experimental results, leading to incorrect d-d hybridizations. By using the Hubbard U correction to adjust the d-bands to the correct position, the discrepancies in GGA calculations are eliminated. Our finding that the correct d-bands position is the key to characterize Cu-TMs, which can be achieved efficiently by applying the Hubbard U correction.

The effects of high pressure up to 24 GPa on carbon nitride were studied using in situ micro photoluminescence (PL) and infrared (IR) absorption measurements at room temperature. The experiments indicate pressure-induced PL quenching with pressure increasing from 0 to 7 GPa, but the PL remains unchanged from 7 to 24 GPa. The PL results display the pressure effect of PL enhancement after release of pressure to ambient atmosphere. The IR absorption bands broaden toward low frequency after release of pressure. These may be explained by using the PL model of undistorted sp${}^2$ clusters, which, as PL centers, undergo distortion under pressure and pressure-induced local atomic rearrangement in the sample.

An efficient light trapping scheme named as textured conductive photonic crystal (TCPC) has been proposed and then applied as a back-reflector (BR) in n-i-p hydrogenated amorphous silicon (a-Si:H) solar cell. This TCPC BR combined a flat one-dimensional photonic crystal and a randomly textured surface of chemically etched ZnO:Al. Total efficiency enhancement was obtained thanks to the sufficient conductivity, high reflectivity and strong light scattering of the TCPC BR. Unwanted intrinsic losses of surface plasmon modes are avoided. An initial efficiency of 9.66% for a-Si:H solar cell was obtained with short-circuit current density of 14.74 mA/cm², fill factor of 70.3%, and open-circuit voltage of 0.932 V.

Properties of pressurized MnSe were investigated based on the first-principles methods using exchange–correlation functionals of the local density approximation (generalized gradient approximation) with and without the Hubbard U correction. Our results show that the Hubbard U (U = 4 eV) correction is necessary to correctly describe the phase transition behaviors of MnSe. We found that at the static condition, phase transitions from the low-temperature phase with a NiAs-type structure (P6₃/mmc) to the P4/nmm phase at 50.5 GPa and further to the Pnma phase at 81 GPa are observed. However, if the transition starts from the room-temperature phase with a NaCl-type structure (Fm-3m), the transition-sequences and -pressures will be different, indicating that temperature can strongly affect the phase transition behaviors of MnSe. Furthermore, we found that pressure-induced negative charge transfer will promote spin crossover. The calculated superconducting properties of the Pnma phase indicate that it may be an unconventional superconductor.