Retinitis pigmentosa (RP) is a pathological condition associated with blindness due to progressive retinal degeneration. RP-linked mutations lead to changes at the retinal binding pocket and in the absorption spectra. Here, we evaluate the geometries, electronic effects, and vertical excitation energies in the dark state of mutated human rhodopsins carrying the abnormal substitutions M207R or S186W at the retinal binding pocket. Two models are used, the solvated protein and the protein in a solvated POPC lipid bilayer. We apply homology modeling, classical molecular dynamics simulations, density functional theory (DFT), and quantum mechanical/molecular mechanical (QM/MM) methods. Our results for the wild type bovine and human rhodopsins, used as a reference, are in good agreement with experiment. For the mutants, we find less twisted QM/MM ground-state chromophore geometries around the C(11)-C(12) double bond and substantial blue shifts in the lowest vertical DFT excitation energies. An analysis of the QM energies shows that the chromophore-counterion region is less stable in the mutants compared to the wild type, consistent with recent protein folding studies. The influence of the mutations near the chromophore is discussed in detail to gain more insight into the properties of these mutants. The spectral tuning is mainly associated with counterion effects and structural features of the retinal chain in the case of the hM207R mutant, and with the presence of a neutral chromophore with deprotonated Lys296 in the case of the hS186W mutant.

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Hybrid organic-inorganic perovskites are semiconductors with disordered structures and remarkable properties for photovoltaic applications. Many theoretical investigations have attempted to obtain structural models of the high-temperature phases, but most of them are focused on the mobility of organic components and their implications in material properties. Herein we propose a set of geometric variables to evaluate the conformation of the inorganic framework at each phase of methylammonium lead iodide perovskite. We show that the analysis of these variables is required to ensure consistent structural models of the tetragonal phase. We explore the theoretical ingredients needed to achieve good models of this phase. Ab initio molecular dynamic simulation, under canonical ensemble at the experimental unit cell volume, leads to representative states of the phase. Under this scheme, PBE and van der Waals density functional approaches provide similar models of the tetragonal phase. We find that this perovskite has a highly mobile inorganic framework due to the thermal effect regardless of movement of the organic cations. Consequently, the electronic structure shows significant movements of the bands with large bandgap variations.FONDECYT of CONICYT-Chile 3150174 1150538 Ministerio de Economia y Competitividad of Spain - Comunidad de Madrid, Spain ENE2013-46624 P 2013/MAE-278

Characterization and control of surfaces and interfaces are critical for photovoltaic and photocatalytic applications. In this work, we propose CH 3 NH 3 PbI 3 (MAPI) perovskite slab models whose energy levels, free of quantum confinement, explicitly consider the spin−orbit coupling and thermal motion. We detail methodological tools based on the density functional theory that allow achieving these models at an affordable computational cost, and analytical corrections are proposed to correct these effects in other systems. The electronic state energies with respect to the vacuum of the static MAPI surface models, terminated in PbI 2 and MAI atomic layers, are in agreement with the experimental data. The PbI 2 -terminated slab has in-gap surface states, which are independent of the thickness of the slab and also of the orientation of the cation on the surface. The surface states are not useful for alignments in photovoltaic devices, while they could be useful for photocatalytic reactions. The energy levels calculated for the MAIterminated surface coincide with the widely used values to estimate the MAPI alignment with the charge transport materials, i.e., −5.4 and −3.9 eV for valence band maximum and conduction band minimum, respectively. Our study offers these slab models to provide guidelines for optimal interface engineering.