More Like this

1. Ab initio nonadiabatic molecular dynamics of charge carriers in metal halide perovskites

   https://doi.org/10.1039/d1nr01990b  

   Li, Wei; She, Yalan; Vasenko, Andrey S.; Prezhdo, Oleg V. (June 2021, Nanoscale)

   Photoinduced nonequilibrium processes in nanoscale materials play key roles in photovoltaic and photocatalytic applications. This review summarizes recent theoretical investigations of excited state dynamics in metal halide perovskites (MHPs), carried out using a state-of-the-art methodology combining nonadiabatic molecular dynamics with real-time time-dependent density functional theory. The simulations allow one to study evolution of charge carriers at the ab initio level and in the time-domain, in direct connection with time-resolved spectroscopy experiments. Eliminating the need for the common approximations, such as harmonic phonons, a choice of the reaction coordinate, weak electron–phonon coupling, a particular kinetic mechanism, and perturbative calculation of rate constants, we model full-dimensional quantum dynamics of electrons coupled to semiclassical vibrations. We study realistic aspects of material composition and structure and their influence on various nonequilibrium processes, including nonradiative trapping and relaxation of charge carriers, hot carrier cooling and luminescence, Auger-type charge–charge scattering, multiple excitons generation and recombination, charge and energy transfer between donor and acceptor materials, and charge recombination inside individual materials and across donor/acceptor interfaces. These phenomena are illustrated with representative materials and interfaces. Focus is placed on response to external perturbations, formation of point defects and their passivation, mixed stoichiometries, dopants, grain boundaries, and interfaces of MHPs with charge transport layers, and quantum confinement. In addition to bulk materials, perovskite quantum dots and 2D perovskites with different layer and spacer cation structures, edge passivation, and dielectric screening are discussed. The atomistic insights into excited state dynamics under realistic conditions provide the fundamental understanding needed for design of advanced solar energy and optoelectronic devices. 

   more » « less
2. Ab initio molecular dynamics study of sodium NMR chemical shifts in the methylamine solution of [Na ⁺ [2.2.2]cryptand Na ⁻ ]

   https://doi.org/10.1039/D0CP06012G  

   Abella, Laura; Philips, Adam; Autschbach, Jochen (January 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   The sodium anion (Na − ) was once thought to behave like a ‘genuine’ anion, with both the [Ne] core and the 3s valence shell interacting very weakly with their environments. In the present work, following a recent study of the surprisingly small quadrupolar line widths of Na − , NMR shielding calculations were carried out for the Na − /Na + [2.2.2]cryptand system solvated in methylamine, based on ab initio molecular dynamics simulations, followed by detailed analyses of the shielding constants. The results confirm that Na − does not act like a quasi-free ion that interacts only weakly with its surroundings. Rather, the filled 3s shell of Na − interacts strongly with its chemical environment, but only weakly with the ion's own core and the nucleus, and it isolates the core from the chemical environment. As a consequence, the Na − ion appears in NMR experiments like a free ion. 

   more » « less
3. Atomistic understanding of structural evolution, ion transport and oxygen stability in layered NaFeO ₂

   https://doi.org/10.1039/c8ta10767j  

   Gao, Yurui; Wang, Zhaoxiang; Lu, Gang (February 2019, Journal of Materials Chemistry A)

   α-NaFeO 2 shares a structure similar to many layered electrode materials in Li-ion and Na-ion batteries. In this work, first-principles calculations are carried out to gain atomistic understanding of structural evolution, ion transport and oxygen stability in NaFeO 2 . Based on the calculation results, we provide an atomistic description of phase transition and structural changes during the charging process. Meanwhile, we identify a di-vacancy assisted diffusion mechanism for Na ions and estimate the diffusion barrier that agrees with experimental data. Furthermore, we reveal that lattice strains could modulate both ion transport and oxygen stability in NaFeO 2 . A moderate 3% tension in the out-of-plane direction could render the ion diffusion barrierless. Moreover, it is predicted that in-plane compressions can stabilize oxygen and suppress oxygen evolution at high potentials. Thus, a combination of the out-of-plane tension with the in-plane compression is expected to reduce the diffusion barrier and stabilize oxygen simultaneously. 

   more » « less
4. Optical transitions of neutral Mg in Mg-doped β -Ga2O3

   https://doi.org/10.1063/5.0081925  

   Bhandari, Suman; Lyons, John_L; Wickramaratne, Darshana; Zvanut, M_E (February 2022, APL Materials)

   Gallium oxide when doped with Mg becomes semi-insulating and can be useful for power electronic devices. The present work investigates optical transitions of neutral Mg (MgGa0) using photoinduced electron paramagnetic resonance spectroscopy, a variation of the traditional optical absorption. Steady-state and time-dependent measurements are carried out at 130 K by illuminating the samples with photon energies from 0.7 to 4.4 eV. Interpretation of the data using a model that incorporates electron–phonon coupling yields a defect transition level that is consistent with the MgGa−/0 level obtained from hybrid density functional theory calculations. We conclude that the neutral to negative transition of MgGa that we observe involves an electron transition from the valence band to the defect, and the MgGa−/0 level is located 1.2 eV above the valence band maximum, with a relaxation energy of 1.3 eV. 

   more » « less
5. Tandem‐trapped ion mobility spectrometry/mass spectrometry coupled with ultraviolet photodissociation

   https://doi.org/10.1002/rcm.9192  

   Liu, Fanny_C; Ridgeway, Mark_E; Winfred, J_S_Raaj_Vellore; Polfer, Nicolas_C; Lee, Jusung; Theisen, Alina; Wootton, Christopher_A; Park, Melvin_A; Bleiholder, Christian (September 2021, Rapid Communications in Mass Spectrometry)

   RationaleTandem‐ion mobility spectrometry/mass spectrometry methods have recently gained traction for the structural characterization of proteins and protein complexes. However, ion activation techniques currently coupled with tandem‐ion mobility spectrometry/mass spectrometry methods are limited in their ability to characterize structures of proteins and protein complexes. MethodsHere, we describe the coupling of the separation capabilities of tandem‐trapped ion mobility spectrometry/mass spectrometry (tTIMS/MS) with the dissociation capabilities of ultraviolet photodissociation (UVPD) for protein structure analysis. ResultsWe establish the feasibility of dissociating intact proteins by UV irradiation at 213 nm between the two TIMS devices in tTIMS/MS and at pressure conditions compatible with ion mobility spectrometry (2–3 mbar). We validate that the fragments produced by UVPD under these conditions result from a radical‐based mechanism in accordance with prior literature on UVPD. The data suggest stabilization of fragment ions produced from UVPD by collisional cooling due to the elevated pressures used here (“UVnoD2”), which otherwise do not survive to detection. The data account for a sequence coverage for the protein ubiquitin comparable to recent reports, demonstrating the analytical utility of our instrument in mobility‐separating fragment ions produced from UVPD. ConclusionsThe data demonstrate that UVPD carried out at elevated pressures of 2–3 mbar yields extensive fragment ions rich in information about the protein and that their exhaustive analysis requires IMS separation post‐UVPD. Therefore, because UVPD and tTIMS/MS each have been shown to be valuable techniques on their own merit in proteomics, our contribution here underscores the potential of combining tTIMS/MS with UVPD for structural proteomics. 

   more » « less