First-Principles Calculation of the Shift Current Bulk Photovoltaic Effect from Carrier Recombination

Physical Review Letters · 2026-02-13

The bulk photovoltaic effect, which occurs in single-phase, noncentrosymmetric materials, is characterized by two primary mechanisms-the ballistic current and the shift current-that each generate dc current during carrier excitation. The excitation shift current in particular has intriguing properties, including ultrafast time evolution, a deep connection to wave function quantum geometry, and a well-established sensitivity to light frequency, optical polarization, material strain and strain gradients, coexisting dc electric fields, and more. Shift photocurrent from excitation has been explored in a variety of real materials using ab initio calculations, but shift current from carrier recombination, while predicted in model systems, has not been explored in real materials. To address this gap, we present a method to calculate the shift current due to carrier recombination under steady-state illumination using first-principles calculations. We then model the response of GaN and several other wurtzite semiconductors under realistic experimental conditions. These results show that recombination current may be comparable in magnitude to excitation shift current and demonstrate that even simple materials exhibit significant variations in recombination shift current that are jointly controlled by material properties and illumination conditions. As relaxation processes may depend on spin and valley degrees of freedom, this Letter enables new possibilities to understand and control the interplay between excitation and recombination shift currents that respond sensitively to electronic, magnetic, structural, and topological factors.

Computational dataset for: How unconventional oxidation state Au2+ is stabilized in halide perovskite Cs4Au3Cl12: a first-principles study of its polaron crystal nature

Zenodo (CERN European Organization for Nuclear Research) · 2026-04-15

DFT inputs and outputs used for the paper "How unconventional oxidation state Au2+ is stabilized in halide perovskite Cs4Au3Cl12: a first-principles study of its polaron crystal nature" (https://arxiv.org/abs/2602.11572). scf.zip: the main self-consistent force calculation COHP.zip: COHP analysis with LOBSTER code bandstruct1.zip, bandstruct2.zip, and bandstruct3.zip: Bandstructure calculations

Band-like Optical Signatures of Ti ₃ C ₂ T <i> _x </i> MXenes

The Journal of Physical Chemistry C · 2026-01-27 · 4 citations

MXenes have shown great potential in electronic and optoelectronic applications. However, the optical properties of these highly conductive two-dimensional materials are not fully understood. The broad near-infrared (IR) optical extinction (∼1.5 eV) in Ti3C2Tx with mixed terminations (Tx: ═O, −OH, −F, −Cl) has been widely attributed to a localized surface plasmon resonance (LSPR). However, previous simulations suggest this peak may be due to an interband transition (IBT). Here, we show that the real component of the dielectric constant of Ti3C2Tx at this peak is positive (ε1 > 0), as measured by spectroscopic ellipsometry (SE), ruling out the possibility of LSPR. Moreover, this band nearly vanishes for experimentally synthesized chlorine-terminated Ti3C2Cl2. Density functional theory (DFT) calculations confirm an IBT origin for this band, specifically due to the oxygen terminations (Ti3C2O2). Metallic behavior is only experimentally observed below 1 eV (ε1 < 0), and DFT calculations predict surface plasmon polaritons (SPPs) in the mid-IR (∼0.5 eV, outside the optical domain) and only for Ti3C2O2, but not for Ti3C2Cl2 or other terminations. Additionally, we demonstrate that making thicker Ti3C2Tx MXene films and/or removing the intercalated water can induce a blue shift in this IBT due to the influence of water in facilitating the out-of-plane conductivity. The IBT assignment is critical because its light-matter interaction is fundamentally different from that of an LSPR, providing a new foundation for designing innovative MXene-based optoelectronic materials, which can be tailored through their termination states, while an LSPR would be insensitive to such synthetic variations.

Computational dataset for: How unconventional oxidation state Au2+ is stabilized in halide perovskite Cs4Au3Cl12: a first-principles study of its polaron crystal nature

Zenodo (CERN European Organization for Nuclear Research) · 2026-04-15

DFT inputs and outputs used for the paper "How unconventional oxidation state Au2+ is stabilized in halide perovskite Cs4Au3Cl12: a first-principles study of its polaron crystal nature" (https://arxiv.org/abs/2602.11572). scf.zip: the main self-consistent force calculation COHP.zip: COHP analysis with LOBSTER code bandstruct1.zip, bandstruct2.zip, and bandstruct3.zip: Bandstructure calculations

Data from: Choosing tight-binding models for accurate optoelectronic responses

Open MIND · 2026-01-29

Tight-binding models provide great insight and are a low-cost alternative to ab initio methods for the calculation of a material’s electronic structure. These models are used to calculate optical responses, including nonlinear optical effects such as the shift current bulk photovoltaic effect. The validity of tight-binding models is often evaluated by comparing their band structures to those calculated with density functional theory. However, we find that band structure agreement is a necessary but not sufficient condition for accurate optical response calculations. We compute the shift current response and dielectric tensor using a variety of tight-binding models of MoS2, including both Slater-Koster and Wannier tight-binding models that treat the Mo 4d orbitals and/or S 3p orbitals. We also truncate hoppings in the Wannier function models to next-nearest-neighbor, as is common in tight-binding methods, in order to gauge the effect on optical response. By examining discrepancies in energies and optical matrix elements, we determine the interpolation quality of the different tight-binding models and establish that agreement in both band structure and wave functions is required to accurately model optical response.

Data and code from: Bridging experiment and theory of relaxor ferroelectrics with multislice electron ptychography

Open MIND · 2026-03-11

Introducing structural and/or chemical heterogeneity into otherwise ordered crystals can dramatically alter material properties. Lead-based relaxor ferroelectrics, such as 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3, are prototypical examples. Here, we perform three-dimensional volumetric characterization using multislice electron ptychography (MEP) and bond valence molecular dynamics (BVMD) simulations. Real-space comparisons between the two under varying strain states reveal a coherent three-dimensional view of the "polar slush." Dipolar correlations from the atomic to domain scales are shown to be jointly modulated by strain and chemical configurations, with the best agreement found in a model accounting for both overall chemical disorder and residual short-range order. Together, MEP and BVMD demonstrate a framework for connecting atomic-scale heterogeneity in complex materials through complementary 3D imaging and predictive modeling.

Data from: Solid-state hydroxide ion conductivity in silver(I) oxide, Ag₂O

DRYAD · 2025-12-30

Silver(I) oxide, Ag2O, precipitated as microcrystals by combining aqueous silver(I) nitrate and KOH solutions, was found to be a solid-state hydroxide ion conductor with ionic conductivity on the order of 10–3 S/cm. The proton chemical shifts at 4.87 and −7.35 ppm measured by solid-state 1H NMR experiments are attributed to water molecules and in-lattice OH– coordinated to silver, respectively. The lack of spinning sidebands around the 4.87 ppm peak indicates rapid reorientation on the NMR time scale, suggesting that the water molecules are adsorbed to the surface of the Ag2O crystals. Pulsed field gradient measurements gave similar diffusion coefficients (2 × 10–7 cm2/s at 298 K) for all three proton environments, indicating chemical exchange between sites on the millisecond time scale. The activation energy for OH– diffusion measured by NMR (0.18 eV) was comparable to that obtained by conductivity measurements and density functional theory (DFT) electronic structure calculations. The calculated Pourbaix diagram of Ag2O is consistent with the slightly lower sample density observed in He pycnometry and thermogravimetric measurements. The dataset here contains the theoretical calculations of this study to support the experimental results, including electronic band structure calculation, geometry relaxation, NMR calculations, and ion-migration calculations.

Tuning Water Transport through Nanochannels of Robust Cation‐Intercalated Ti₃C₂T_<i>x</i> MXene Membranes

ChemSusChem · 2025-08-13 · 3 citations

Ti 3 C 2 T x MXene membranes have attracted considerable interest due to their exceptional water transport properties, yet the role of cation intercalation on governing transport remains poorly understood. In this experimental and theoretical study, it shows how intercalation with K + , Na + , Li + , Ca 2+ , and Mg 2+ modulates both the nanochannel architecture and water flux of Ti 3 C 2 T x membranes. Unlike in graphene oxide analogs, cations with larger hydration diameters in Ti 3 C 2 T x expand the interlayer spacing, widening flow channels, enhancing slip length of these nanochannels, and boosting water flux from 31.45 to 61.86 L m −2 h −1 . To overcome intrinsically poor adhesion of Ti 3 C 2 T x to polymeric supports, this study incorporates a thin polyvinyl‐alcohol interlayer, which substantially enhances mechanical robustness and structural integrity. Together, these findings elucidate how cation hydration controls water transport and offer a flexible strategy for tailoring MXene membrane performance.

Observation of polarization density waves in SrTiO3

Nature Physics · 2025-04-07 · 7 citations

The nature of the incipient ferroelectric transition in SrTiO3 has been a long-standing puzzle in condensed matter physics. One explanation involves the competition between ferroelectricity and an instability characterized by the mesoscopic modulation of the polarization. These polarization density waves, which should intensify near the quantum critical point, break local inversion symmetry and are difficult to characterize with conventional X-ray scattering methods. Here we probe inversion symmetry breaking at finite momenta and visualize the instability of the polarization at the nanometre scale in SrTiO3 by combining a femtosecond X-ray free-electron laser with terahertz coherent control methods. We found polar-acoustic collective modes that are soft, particularly at the tens of nanometre scale. These precursor collective excitations provide evidence for the conjectured mesoscopic-modulated phase in SrTiO3. Despite exhibiting ferroelectric features, SrTiO3 fails to display long-range polar order at low temperatures due to quantum fluctuations. An ultrafast X-ray diffraction experiment now probes polar dynamics of this material at the nanometre scale.

Studies of the mechanically induced reactivity of graphene with water using a 2D-materials strain reactor

DRYAD · 2025-12-11

This dataset supports the investigation of strain-dependent reactivity with water on distorted graphene membranes using Raman microspectroscopy and density functional theory (DFT) calculations. Excel spreadsheets (.xlsx) relay the processed Raman micro spectroscopy data from the raw data .wip files (software for Witec Project analysis software) The dataset also includes raw outputs from DFT calculations used to construct simulated reaction energy landscapes describing water dissociation on graphene under applied strain. These data provide the guide to study strain-engineered reactivity in low-dimensional systems.