Among the important family of halide perovskites, one particular case of all-inorganic, 0-D CsPbBr and 3-D CsPbBr-based nanostructures and thin films is witnessing intense activity due to ultrafast luminescence with high quantum yield. To understand their emissive behavior, we use hybrid density functional calculations to first compare the ground-state electronic structure of the two prospective compounds. The dispersive band edges of CsPbBr do not support self-trapped carriers, which agrees with reports of weak exciton binding energy and high photocurrent. The larger gap 0-D material CsPbBr, however, reveals polaronic and excitonic features. We show that those lattice-coupled carriers are likely responsible for observed ultraviolet emission around ∼375 nm, reported in bulk CsPbBr and CsPbBr/CsPbBr composites. Ionization potential calculations and estimates of type-I band alignment support the notion of quantum confinement leading to fast, green emission from CsPbBr nanostructures embedded in CsPbBr.

Carbon nanodots (CDs) were initially synthesized by dehydrating carbohydrates using a commercial household microwave (700 W). To prepare BN-CD, 960 mg of citric acid (5.0 mmol, Aldrich) and 310 mg of boric acid (5.0 mmol) were dissolved in 10 mL of water. To this transparent solution, 347 µL of EDA (5.0 mmol) was added under vigorous stirring for 2 min. The solution was placed into a microwave oven and heated for 2 min, and a yellow solid was obtained after cooling to room temperature. The solid was diluted in 5.0 mL of water. The yellow suspension was dialyzed (SpectraPore MWCO 500 -1,000) for 2 days to remove salts and unreacted chemicals. To synthesize N-CD, microwave pyrolysis was performed in the absence of boric acid. BN-CD0.5 and BN-CD2 were prepared with 2.5 mmol (0.5 equiv. of citric acid and ethylene diamine) and 10 mmol (2 equiv. of citric acid and ethylene diamine) of boric acid, with the same concentrations of other precursors as described above. Non-doped plain CD was synthesized with 5 mmol of citric acid through hydrothermal method at 180 o C for 6 hr. B-CD was synthesized with 5 mmol of boric acid and citric acid.

ComDMFT is a massively parallel computational package to study the electronic structure of correlated-electron systems (CES). Our approach is a parameterfree method based on ab initio linearized quasiparticle self-consistent GW (LQSGW) and dynamical mean field theory (DMFT). The non-local part of the electronic self-energy is treated within ab initio LQSGW and the local strong correlation is treated within DMFT. In addition to ab initio LQSGW+DMFT, charge selfconsistent LDA+DMFT methodology is also implemented, enabling multiple methods in one open-source platform for the electronic structure of CES. This package can be extended for future developments to implement other methodologies to treat CES. PROGRAM SUMMARY/NEW VERSION PROGRAM SUMMARYProgram Title: ComDMFT Licensing provisions(please choose one): GPLv3 Programming language: fortran90, C++, and Python Nature of problem:There is no open-source code based on ab initio GW+EDMFT and related methodologies to support their theoretical advancement for the electronic structure of correlated electron systems. Solution method:We implemented ab initio LQSGW+DMFT methodology, as a simplification of ab initio GW+EDMFT, for the electronic structure of correlated electron systems. In addition, charge self-consistent LDA+DMFT methodology is also implemented, enabling the comparison of multiple methods for the electronic structure of correlated electron systems in one platform. Additional comments:ComDMFT is built on top of Wannier90 [1] and FlapwMBPT [2] codes.

The recent and exciting discovery of superconductivity in the hole-doped infinite-layer nickelate Nd 1−δ Sr δ NiO2 draws strong attention to correlated quantum materials. From a theoretical view point, this new class of unconvential superconducting materials provide an opportunity to unveil new physics in correlated quantum materials. Here we study the temperature and doping dependence of the local spectrum of the charge, spin and orbital susceptibilities from first principles. By using ab initio LQSGW+DMFT methodology, we show that onsite Hund's coupling in Ni-d orbitals gives rise to multiple signatures of Hund's metallic phase in Ni-eg orbitals. The proposed picture of the nickelates as an eg (two orbit) Hund's metal differs from the picture of the Fe-based superconductors as a five orbital Hund's metal as well as the picture of the cuprates as doped charge transfer insulators. Our finding unveils a new class of the Hunds metals and has potential implications for the broad range of correlated two orbital systems away from half-filling.

Hybrid organic–inorganic perovskites (CH3NH3PbI3) have gained prominence in recent years due to their fascinating electronic properties and potential for commercial application in photovoltaics and optoelectronics. One of their intriguing features is in the structure itself and the role played by the organic cation CH3NH3 + (MA+). In this study, we implement first-principles-based methods to take a static look at this dynamic system, which may shed some light on the preferential orientation of MA+ and its impact. We find there is a lattice energy gain in cubic CH3NH3PbI3, when going from a pristine host supercell with [100] MA+ orientation to a distorted host consisting of preferentially aligned MA+ and tilted PbI6 octahedra. Reoriented MA+ and octahedral tilting are also accompanied by larger number of (N–H3)···I hydrogen bonds. This lattice reconfiguration may support charge localization as evidenced by larger 216-atom supercell calculations. The localization behavior is a consequence of lattice polarization (reoriented MA+ and tilted octahedra) which spreads across multiple unit cells and thus may not be strongly bound small polarons.

There has been considerable speculation over the nature of charge carriers in organic-inorganic hybrid perovskites, i.e., whether they are free and band-like, or they are prone to self-trapping via short range deformation potentials. Unusually long minority-carrier diffusion lengths and moderate-to-low mobilities, together with relatively few deep defects add to their intrigue. Here we implement density functional methods to investigate the room-temperature, tetragonal phase of CHNHPbI. We compare charge localization behavior at shallow levels and associated lattice relaxation versus those at deep polaronic states. The shallow level originates from screened Coulomb interaction between the perturbed host and an excited electron or hole. The host lattice has a tendency towards forming these shallow traps where the electron or hole is localized not too far from the band edge. In contrast, there is a considerable potential barrier that must be overcome in order to initiate polaronic hole trapping. The formation of a hole polaron (I center) involves strong lattice relaxation, including large off-center displacement of the organic cation, CHNH. This type of deep polaron is energetically unfavorable, and active shallow traps are expected to shape the carrier dynamics in this material.

Several members of a large family of perovskite-like halides with a common chemical formula, ABX3 (A  =  monovalent, B  =  divalent, and X  =  halogen ion), are being investigated for their interesting properties and potential technological applications. CsCaI3 and KCaI3 are two such ionic compounds who are of interest in the quest for superior and cost-effective alternatives to NaI or CsI based scintillators. They are the subject of this first-principles based computational study. Both are wide-gap materials having primarily I 5p and Ca 3d characters near the valence and conduction band edges, respectively. Although built from [CaI6] octahedral motifs, structural differences between the two compounds is reflected in anisotropic electron effective mass and distinctive formation and migration of self-trapped holes. We discuss these properties as they relate to scintillation decay and proportional light yield.

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