Advanced potential energy surfaces are defined as theoretical models that explicitly include many-body effects that transcend the standard fixed-charge, pairwise-additive paradigm typically used in molecular simulation. However, several factors relating to their software implementation have precluded their widespread use in condensed-phase simulations: the computational cost of the theoretical models, a paucity of approximate models and algorithmic improvements that can ameliorate their cost, underdeveloped interfaces and limited dissemination in computational code bases that are widely used in the computational chemistry community, and software implementations that have not kept pace with modern high-performance computing (HPC) architectures, such as multicore CPUs and modern graphics processing units (GPUs). In this Feature article we review recent progress made in these areas, including well-defined polarization approximations and new multipole electrostatic formulations, novel methods for solving the mutual polarization equations and increasing the MD time step, combining linear scaling electronic structure methods with new QM/MM methods that account for mutual polarization between the two regions, and the greatly improved software deployment of these models and methods onto GPU and CPU hardware platforms. We have now approached an era where multipole-based polarizable force fields can be routinely used to obtain computational results comparable to state-of-the-art density functional theory while reaching sampling statistics that are acceptable when compared to that obtained from simpler fixed partial charge force fields.
Series of amorphous SiO2, ZrO2 and HfO2 films were prepared by electron-beam evaporation at various oxygen pressures such that the packing density varied from 0.6 to 0.82. Transmittance spectra were evaluated with respect to thickness and refractive index by application of analytical formulas to the interference extrema and by dielectric modeling. The thickness of the films ranged from 150 to 1500 nm. The coefficients of Cauchy and Sellmeier dispersion curves were determined as a function of the packing density. The mass density of the compact amorphous grains was estimated by an effective-medium theory and a general refractivity formula. It is similar to those of the crystalline materials. We used the optical data to design multilayer coatings for laser applications in a broad spectral range, including the UV.
Optical transmittance spectra of In2O3 : Sn (ITO) films were simulated with a computer program based on dielectric modelling. The films were prepared by radiofrequency sputtering under various oxygen fluxes such that the carrier density varies from 3×1019 to 1.5×1021 cm-3. The dielectric function used is the sum of three types of electronic excitations: intraband transitions of free electrons (Drude model), band gap transitions, and interband transitions into the upper half of the conduction band. The parameters of these excitations are evaluated as a function of the carrier density. The damping in the Drude term was modelled frequency-dependent to account for the low extinction coefficient observed in the visible spectral range. The parameters resulting from the optical measurements were compared with those from the electrical measurements. Both the optical mobility and carrier density are found to be higher than those of the respective electric parameters. These discrepancies are attributed to a pronounced microstructure with badly conducting grain boundaries. The refractive index at 550 nm decreases linearly with increasing electron concentration. This is due both to the shift of the plasma edge and the Burstein-Moss shift of the band edge. All band gap transitions go up to the Fermi level.
Mn‐doping in cesium lead halide perovskite nanoplatelets (NPls) is of particular importance where strong quantum confinement plays a significant role towards the exciton–dopant coupling. In this work, we report an immiscible bi‐phasic strategy for post‐synthetic Mn‐doping of CsPbX3 (X=Br, Cl) NPls. A systematic study shows that electron‐donating oleylamine acts as a shuttle ligand to transport MnX2 through the water–hexane interface and deliver it to the NPls. The halide anion also plays an essential role in maintaining an appropriate radius of Mn2+ and thus fulfilling the octahedral factor required for the formation of perovskite crystals. By varying the thickness of parent NPls, we can tune the dopant incorporation and, consequently, the exciton‐to‐dopant energy transfer process in doped NPls. Time‐resolved optical measurements offer a detailed insight into the exciton‐to‐dopant energy transfer process. This new approach for post‐synthetic cation doping paves a way towards exploring the cation exchange process in several other halide perovskites at the polar–nonpolar interface.
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