Ab initio quantum dynamics of charge carriers in graphitic carbon nitride nanosheets

Energy-Conserving Surface Hopping for Auger Processes

Auger-type processes are ubiquitous in nanoscale materials because quantum confinement enhances Coulomb interactions, and there exist large densities of states. Modeling Auger processes requires the modification of nonadiabatic (NA) molecular dynamics algorithms to include transitions caused by both NA and Coulomb couplings. The system is split into quantum and classical subsystems, e.g., electrons and vibrations, and as a result, energy conservation becomes nontrivial. In surface hopping, an electronic transition induced by NA coupling is accompanied by a classical velocity readjustment to ensure conservation of the total quantum-classical energy. A different treatment is needed for Auger transitions driven by Coulomb interactions. We develop a nonadiabatic molecular dynamics methodology that meticulously differentiates the energy redistribution accompanying hops induced by the NA coupling and the Coulomb interaction and correctly conserves the total energy at each transition. If the transition is driven by a Coulomb interaction, the hop energy is redistributed within the quantum electronic subsystem only. If the transition is NA, the energy is redistributed between the quantum and classical subsystems. Properly maintaining energy conservation for both types of transitions is crucial to generate a correct order of events, obtain accurate transition times, maintain a proper statistical distribution of state populations, and reach thermodynamic equilibrium. We test the method with biexciton annihilation and Auger-assisted hot electron relaxation in a CdSe quantum dot. The sequence of Auger and phonon-driven processes and the calculated time scales are in excellent agreement with the experimental results. The developed approach can be coupled with any surface-hopping method and provides a crucial practical advance to study charge-carrier dynamics in the nanoscale and condensed matter systems.

Emergence of Z-Scheme Photocatalysis for Total Water Splitting: An Improvised Route to High Efficiency

Photocatalytic water splitting to spontaneously produce H2 and O2 is a long-standing goal in solar energy conversion, presenting a significant challenge without using sacrificial electron donors or external biases. Inspired by natural photosynthesis, the design of artificial Z-scheme photocatalytic systems is at the forefront of this field. These systems achieve higher redox potential by separating photogenerated electrons and holes through a fast interlayer recombination process between valence and conduction band edges. Z-scheme photocatalysis involves using two different semiconductors with distinct bandgap energies. Here, we explore potential systems based on two-dimensional (2D) heterostructures composed of carbon, nitrogen, or similar main group elements. The advantages and disadvantages of these systems are discussed, with a focus on enhancing their efficiency through strategic design. Special emphasis is placed on the dynamics of excited charge carrier transfer and recombination processes, which are crucial for developing efficient photocatalytic systems for overall water splitting.

Nonadiabatic molecular dynamics with subsystem density functional theory: application to crystalline pentacene

In this work, we report the development and assessment of the nonadiabatic molecular dynamics approach with the electronic structure calculations based on the linearly scaling subsystem density functional method. The approach is implemented in an open-source embedded Quantum Espresso/Libra software specially designed for nonadiabatic dynamics simulations in extended systems. As proof of the applicability of this method to large condensed-matter systems, we examine the dynamics of nonradiative relaxation of excess excitation energy in pentacene crystals with the simulation supercells containing more than 600 atoms. We find that increased structural disorder observed in larger supercell models induces larger nonadiabatic couplings of electronic states and accelerates the relaxation dynamics of excited states. We conduct a comparative analysis of several quantum-classical trajectory surface hopping schemes, including two new methods proposed in this work (revised decoherence-induced surface hopping and instantaneous decoherence at frustrated hops). Most of the tested schemes suggest fast energy relaxation occurring with the timescales in the 0.7-2.0 ps range, but they significantly overestimate the ground state recovery rates. Only the modified simplified decay of mixing approach yields a notably slower relaxation timescales of 8-14 ps, with a significantly inhibited ground state recovery.

Prolonged Exciton Lifetime Is Achieved in Porphyrin Nanoring by Template Engineering: A Nonadiabatic Tight Binding Approach

Porphyrin nanoring has been attracting immense attention due to its light harvesting capacity and potential applications in optical, catalysis, sensor, and electronic devices. We demonstrate by nonadiabatic quantum dynamics simulations that the photovoltaic efficiency can be enhanced by template engineering. Altering the hexadentate template (T6) with two tridentate templates (2T3) within the porphyrin ring (P6) cavity accelerated the electron transfer twice and suppressed the electron-hole recombination by nearly three times. The atomistic tight-binding simulation rationalized the dynamics by different localizations of charge of the band edge states, changes in nonadiabatic coupling, alteration in quantum coherence, and involvement of diverse electron-phonon vibrational modes. Further 2T3 templates more strongly hold the P6 ring than T6, reducing the structural fluctuation. As a result, the nonadiabatic coupling becomes weaker and suppresses the carrier recombination. Current atomistic simulation presents a template engineering strategy to enhance the exciton lifetime along with ultrafast charge separation, crucial factors for photovoltaic applications.

Hot carrier relaxation dynamics of an aza-covalent organic framework during photoexcitation: An insight from ab initio quantum dynamics

In order to develop an efficient metal-free solar energy harvester, we herein performed the electronic structure calculation, followed by the hot carrier relaxation dynamics of two dimensional (2D) aza-covalent organic framework by time domain density functional calculations in conjunction with non-adiabatic molecular dynamics (NAMD) simulation. The electronic structure calculation shows that the aza-covalent organic framework (COF) is a direct bandgap semiconductor with acute charge separation and effective optical absorption in the UV-visible region. Our study of non-adiabatic molecular dynamics simulation predicts the sufficiently prolonged electron-hole recombination process (6.8 nanoseconds) and the comparatively faster electron (22.48 ps) and hole relaxation (0.51 ps) dynamics in this two-dimensional aza-COF. According to our theoretical analysis, strong electron-phonon coupling is responsible for the rapid charge relaxation, whereas the electron-hole recombination process is slowed down by relatively weak electron-phonon coupling, relatively lower non-adiabatic coupling, and quick decoherence time. We do hope that our results of NAMD simulation on exciton relaxation dynamics will be helpful for designing photovoltaic devices based on this two dimensional aza-COF.

Photocatalytic activity of dual defect modified graphitic carbon nitride is robust to tautomerism: machine learning assisted ab initio quantum dynamics

Two-dimensional graphitic carbon nitride (GCN) is a popular metal-free polymer for sustainable energy applications due to its unique structure and semiconductor properties. Dopants and defects are used to tune GCN, and dual defect modified GCN exhibits superior properties and enhanced photocatalytic efficiency in comparison to pristine or single defect GCN. We employ a multistep approach combining time-dependent density functional theory and nonadiabatic molecular dynamics (NAMD) with machine learning (ML) to investigate coupled structural and electronic dynamics in GCN over a nanosecond timescale, comparable to and exceeding the lifetimes of photo-generated charge carriers and photocatalytic events. Although frequent hydrogen hopping transitions occur among four tautomeric structures, the electron-hole separation and recombination processes are only weakly sensitive to the tautomerism. The charge separated state survives for about 10 ps, sufficiently long to enable photocatalysis. The employed ML-NAMD methodology provides insights into rare events that can influence excited state dynamics in the condensed phase and nanoscale materials and extends NAMD simulations from pico- to nanoseconds. The ab initio quantum dynamics simulation provides a detailed atomistic mechanism of photoinduced evolution of charge carriers in GCN and rationalizes how GCN remains photo-catalytically active despite its multiple isomeric and tautomeric forms.

Enhanced Charge Separation in Single Atom Cobalt Based Graphitic Carbon Nitride: Time Domain Ab Initio Analysis

In recent years, single atom catalysts have been at the forefront of energy conversion research, particularly in the field of catalysis. Carbon nitrides offer great potential as hosts for stabilizing metal atoms due to their unique electronic structure. We use ab initio nonadiabatic molecular dynamics to study photoexcitation dynamics in single atom cobalt based graphitic carbon nitride. The results elucidate the positive effect of the doped cobalt atom on the electronic structure of GCN. Cobalt doping produces filled midgap states that serve as oxidation centers, advantageous for various redox reactions. The presence of midgap states enables the harvesting of longer wavelength photons, thereby extending the absorption range of solar light. Although doping accelerates charge relaxation overall, charge recombination is significantly slower than charge separation, creating beneficial conditions for catalysis applications. The simulations reveal the detailed microscopic mechanism underlying the improved performance of the doped system due to atomic defects and demonstrate an effective charge separation strategy to construct highly efficient and stable photocatalytic two-dimensional materials.

Point defect-mediated hot carrier relaxation dynamics of lead-free FASnI3 perovskites

In search of a promising optoelectronic performance, we herein investigated the hot carrier relaxation dynamics of a lead-free cubic phased bulk formamidinium tin triiodide (FASnI3) perovskite. To gain detailed theoretical insights, we should estimate the carrier relaxation dynamics of this pristine perovskite. To control the dynamics, point defects like central tin (Sn), iodine(I) anions, and formamidinium (FA) cations were introduced. With the iodine vacancy in the FASnI3 perovskite, the system seems to be unstable at room temperature, whereas the other three types of FASnI3 perovskites (pristine, Sn vacancy, and FA vacancy) are significantly stable at 300 K having semiconducting nature and excellent optical absorption in the UV-visible range. The computed electron-hole recombination time for the pristine system is 3.9 nanoseconds, which is in good agreement with the experimental investigation. The exciton relaxation processes in Sn and FA vacancy perovskites require 2.8 and 4.8 nanoseconds, respectively. These variations in the hot carrier relaxation dynamics processes are caused by the generation of significant changes in non-adiabatic coupling between energy levels, electron-phonon coupling, and quantum decoherence in different point defect analogous systems. The results presented here offer deeper insight into the temperature-dependent carrier relaxation dynamics of FASnI3 perovskites and thus open up opportunities for future exploration of their optoelectronic properties.

Energy-Conserving and Thermally Corrected Neglect of Back-Reaction Approximation Method for Nonadiabatic Molecular Dynamics

In this work, the energy-conserving and thermally corrected neglect of the back-reaction approximation approach for nonadiabatic molecular dynamics in extended atomistic systems is developed. The new approach introduces three key corrections to the original method: (1) it enforces the total energy conservation, (2) it introduces an explicit coupling of the system to its environment, and (3) it introduces a renormalization of nonadiabatic couplings to account for a difference between the instantaneous nuclear kinetic energy and the kinetic energy of guiding trajectories. In the new approach, an auxiliary kinetic energy variable is introduced as an independent dynamical variable. The new approach produces nonzero equilibrium populations, whereas the original neglect of the back-reaction approximation method does not. It yields population relaxation time scales that are favorably comparable to the reference values, and it introduces an explicit and controllable way of dissipating energy into a bath without an assumption of the bath being at equilibrium.

How the Stacking Pattern Influences the Charge Transfer Dynamics of van der Waals Heterostructures: An Answer from a Time-Domain Ab Initio Study

Here, we perform a time domain density functional study in conjunction with a non-adiabatic molecular dynamics (NAMD) simulation to investigate the charge carrier dynamics in a series of van der Waals heterostructures made of two-dimensional (2D) SnX2 (X = S or Se)-supported ZrS2, ZrSe2, and ZrSSe monolayers. Results from NAMD simulation reveal delayed electron-hole recombination (in the range of 0.53-2.13 ns) and ultrafast electron/hole transfer processes (electron transfer within 108.3-321.5 fs and hole transfer between 107.6 and 258.8 fs). The most interesting finding of our study is that switching from AB to AA stacking in the heterostructures extends the carrier lifespan by a significant amount. The delayed electron-hole recombination because of the switching stacking pattern can be rationalized by weak electron-phonon coupling, lower non-adiabatic coupling (NAC), and fast decoherence time. Thus, these insightful NAMD studies of excited charge carriers reveal that the stacking pattern variation is an effective tool to develop efficient photovoltaic devices based on 2D van der Waals heterostructures.

Alternating current properties of bulk- and nanosheet-graphitic carbon nitride compacts at elevated temperatures

The investigations of temperature-dependent electrical properties in graphitic carbon nitride (g-C3N4) have been largely performed at/below room temperature on devices commonly fabricated by vacuum techniques, leaving the gap to further explore its behaviors at high-temperature. We reported herein the temperature dependence (400 → 35 °C) of alternating current (AC) electrical properties in bulk- and nanosheet-g-C3N4 compacts simply prepared by pelletizing the powder. The bulk sample was synthesized via the direct heating of urea, and the subsequent HNO3-assisted thermal exfoliation yielded the nanosheet counterpart. Their thermal stability was confirmed by variable-temperature X-ray diffraction, demonstrating reversible interlayer expansion/contraction upon heating/cooling with the thermal expansion coefficient of 2.2 × 10-5-3.1 × 10-5 K-1. It is found that bulk- and nanosheet-g-C3N4 were highly insulating (resistivity ρ ∼ 108 Ω cm unchanged with temperature), resembling layered van der Waals materials such as graphite fluoride but unlike electronically insulating oxides. Likewise, the dielectric permittivity ε', loss tangent tan δ, refractive index n, dielectric heating coefficient J, and attenuation coefficient α, were weakly temperature- and frequency-dependent (103-105 Hz). The experimentally determined ε' of bulk-g-C3N4 was reasonably close to the in-plane static dielectric permittivity (8 vs. 5.1) deduced from first-principles calculation, consistent with the anisotropic structure. The nanosheet-g-C3N4 exhibited a higher ε' ∼ 15 while keeping similar tan δ (∼0.09) compared to the bulk counterpart, demonstrating its potential as a highly insulating, stable dielectrics at elevated temperatures.

Quantitative Evaluation of the Carrier Separation Performance of Heterojunction Photocatalysts: The Case of g-C3N4/SrTiO3

Heterojunction photocatalysts are of great interest in the energy and environmental fields, because of their potential to significantly increase the efficiency of harvesting solar energy. Advances in design have been hampered by the continued use of only qualitative analyses. Quantitative evaluation of the carrier separation performance is urgently needed for the design and application of heterojunction photocatalysts. Taking the g-C₃N₄/SrTiO₃ heterojunction as an example, we address the conventional energy band and electronic structure issues by first-principles analysis. After interface coupling, the band edge alignment reverses from that of the respective isolated states of the heterojunction components, suggesting new ways of thinking about the catalytic mechanism of the heterojunction. More significantly, we show the carrier separation performance of heterojunction photocatalysts can be quantitatively predicted by the nonadiabatic molecular dynamics method, enabling more precisely directed research and promoting the quantified design and application of heterojunction photocatalysis, making a contribution of great scientific significance.

Control of Charge Carrier Relaxation at the Au/WSe2 Interface by Ti and TiO2 Adhesion Layers: Ab Initio Quantum Dynamics

Phonon-mediated charge relaxation plays a vital role in controlling thermal transport across an interface for efficient functioning of two-dimensional (2D) nanostructured devices. Using a combination of nonadiabatic molecular dynamics with real-time time-dependent density functional theory, we demonstrate a strong influence of adhesion layers at the Au/WSe₂ interface on nonequilibrium charge relaxation, rationalizing recent ultrafast time-resolved experiments. Ti oxide layers (TiO_x) create a barrier to the interaction between Au and WSe₂ and extend hot carrier lifetimes, creating benefits for photovoltaic and photocatalytic applications. In contrast, a metallic Ti layer accelerates the energy flow, as needed for efficient heat dissipation in electronic devices. The interaction of metallic Ti with WSe₂ causes W-Se bond scissoring and pins the Fermi level. The Ti adhesion layer enhances the electron-phonon coupling due to an increased density of states and the light mass of the Ti atom. The conclusions are robust to presence of typical point defects. The atomic-scale ab initio analysis of carrier relaxation at the interfaces advances our knowledge in fabricating nanodevices with optimized electronic and thermal properties.

Ultrafast Charge Transfer and Delayed Recombination in Graphitic-CN/WTe2 van der Waals Heterostructure: A Time Domain Ab Initio Study

In search of an efficient solar energy harvester, we herein performed a time domain density functional study coupled with nonadiabatic molecular dynamics (NAMD) simulation to gain atomistic insight into the charge carrier dynamics of a graphitic carbon nitride (g-CN)-tungsten telluride (WTe₂) van der Waals heterostructure. Our NAMD study predicted ultrafast electron (589 fs) and hole-transfer (807 fs) dynamics in g-CN/WTe₂ heterostructure and a delayed electron-hole recombination process (2.404 ns) as compared to that of the individual g-CN (3 ps) and WTe₂ (0.55 ps) monolayer. The ultrafast charge transfer is due to strong electron-phonon coupling during the charge-transfer process while comparatively weak electron-phonon coupling, sufficient band gap, comparatively lower nonadiabatic coupling (NAC), and fast decoherence time slow down the electron-hole recombination process. The NAMD results of exciton relaxation dynamics are valuable for insightful understanding of charge carrier dynamics and in designing photovoltaic devices based on organic-inorganic 2D van der Waals heterostructures.

Electron-phonon relaxation at the Au/WSe2 interface is significantly accelerated by a Ti adhesion layer: time-domain ab initio analysis

Thermal transport at nanoscale metal-semiconductor interfaces via electron-phonon coupling is crucial for applications of modern microelectronic, electro-optic and thermoelectric devices. To enhance the device performance, the heat flow can be regulated by modifying the interfacial atomic interactions. We use ab initio time-dependent density functional theory combined with non-adiabatic molecular dynamics to study how the hot electron and hole relaxation rates change on incorporating a thin Ti adhesion layer at the Au/WSe₂ interface. The excited charge carrier relaxation is much faster in Au/Ti/WSe₂ due to the enhanced electron-phonon coupling, rationalized by the following reasons: (1) Ti atoms are lighter than Au, W and Se atoms and move faster. (2) Ti has a significant contribution to the electronic properties in the relevant energy range. (3) Ti interacts strongly with WSe₂ and promotes its bond-scissoring which causes Fermi-level pinning, making WSe₂ contribute to electronic properties around the Fermi level. The changes in the relaxation rates are more pronounced for excited electrons compared to holes because both relative and absolute Ti contributions to the electronic properties are larger above than below the Fermi level. The results provide guidance for improving the design of novel and robust materials by optimizing the heat dissipation at metal-semiconductor interfaces.

Nonadiabatic Molecular Dynamics with Extended Density Functional Tight-Binding: Application to Nanocrystals and Periodic Solids

In this work, we report a new methodology for nonadiabatic molecular dynamics calculations within the extended tight-binding (xTB) framework. We demonstrate the applicability of the developed approach to finite and periodic systems with thousands of atoms by modeling "hot" electron relaxation dynamics in silicon nanocrystals and electron-hole recombination in both a graphitic carbon nitride monolayer and a titanium-based metal-organic framework (MOF). This work reports the nonadiabatic dynamic simulations in the largest Si nanocrystals studied so far by the xTB framework, with diameters up to 3.5 nm. For silicon nanocrystals, we find a non-monotonic dependence of "hot" electron relaxation rates on the nanocrystal size, in agreement with available experimental reports. We rationalize this relationship by a combination of decreasing nonadiabatic couplings related to system size and the increase of available coherent transfer pathways in systems with higher densities of states. We emphasize the importance of proper treatment of coherences for obtaining such non-monotonic dependences. We characterize the electron-hole recombination dynamics in the graphitic carbon nitride monolayer and the Ti-containing MOF. We demonstrate the importance of spin-adaptation and proper sampling of surface hopping trajectories in modeling such processes. We also assess several trajectory surface hopping schemes and highlight their distinct qualitative behavior in modeling the excited-state dynamics in superexchange-like models depending on how they handle coherences between nearly parallel states.

Charge carrier nonadiabatic dynamics in non-metal doped graphitic carbon nitride

Graphitic carbon nitride (GCN) has attracted significant attention due to its excellent performance in photocatalytic applications. Non-metal doping of GCN has been widely used to improve the efficiency of the material as a photocatalyst. Using a combination of time-domain density functional theory with nonadiabatic molecular dynamics, we study the charge carrier dynamics in oxygen and boron doped GCN systems. The reported simulations provide a detailed time-domain mechanistic description of the charge separation and recombination processes that are of fundamental importance while evaluating the photovoltaic and photocatalytic performance of the material. The appearance of smaller energy gaps due to the presence of dopant states improves the visible light absorption range of the doped systems. At the same time, the nonradiative lifetimes are shortened in the doped systems as compared to the pristine GCN. In the case of boron doped at a carbon (B–C–GCN), the charge recombination time is very long as compared to the other two doped systems owing to the smaller electron–phonon coupling strength between the valence band maximum and the trap state. The results suggest B–C–GCN as the most suitable candidate among three doped systems studied in this work for applications in photocatalysis. This work sheds light into the influence of dopants on quantum dynamics processes that govern GCN performance and, thus, guides toward building high-performance devices in photocatalysis.

Excited State Dynamics in Dual-Defects Modified Graphitic Carbon Nitride

Significant efforts are focused on defect-engineering of metal-free graphitic carbon nitride (g-C₃N₄) to amplify its efficacy. A conceptually new multidefect-modified g-C₃N₄ having simultaneously two or more defects has attracted strong attention for its enhanced photocatalytic properties. We model and compare the excited state dynamics in g-C₃N₄ with (i) nitrogen defects (N vacancy and CN group) and (ii) dual defects (N vacancy, CN group, and O doping) and show that the nonradiative recombination of charge carriers in these systems follows the Shockley-Read-Hall mechanism. The nitrogen defects create three midgap states that trap charges and act as recombination centers. The dual-defect modified systems exhibit superior properties compared with pristine g-C₃N₄ because the defects facilitate rapid charge separation and extend the spectrum of absorbed light. The system doped with O shows better performance due to enhanced carrier lifetime and higher oxidation potential caused by a downshifted valence band. The study provides guidance for rational design of stable and efficient photocatalytic materials.

Extending the Time Scales of Nonadiabatic Molecular Dynamics via Machine Learning in the Time Domain

A novel methodology for direct modeling of long-time scale nonadiabatic dynamics in extended nanoscale and solid-state systems is developed. The presented approach enables forecasting the vibronic Hamiltonians as a direct function of time via machine-learning models trained directly in the time domain. The use of periodic and aperiodic functions that transform time into effective input modes of the artificial neural network is demonstrated to be essential for such an approach to work for both abstract and atomistic models. The best strategies and possible limitations pertaining to the new methodology are explored and discussed. An exemplary direct simulation of unprecedentedly long 20 picosecond trajectories is conducted for a divacancy-containing monolayer black phosphorus system, and the importance of conducting such extended simulations is demonstrated. New insights into the excited states photophysics in this system are presented, including the role of decoherence and model definition.

Ultrafast Interlayer Charge Separation, Enhanced Visible-Light Absorption, and Tunable Overpotential in Twisted Graphitic Carbon Nitride Bilayers for Water Splitting

Moiré pattern superlattice formed by 2D van der Waals layered structures have attracted great attention for diverse applications. In experiments, the enhancement of catalytic performance in twisted bilayer systems is reported while its mechanism remains unclear. From high-accuracy first-principles and time-dependent ab initio nonadiabatic molecular dynamics calculations, ultrafast interlayer charge transfer within 120 fs, excellent charge separation, improved visible-light absorption, and satisfactory overpotentials for the hydrogen evolution and oxygen evolution reactions in twisted graphitic carbon nitride (g-C₃ N₄ ) bilayers are found, which are beneficial to photocatalytic, photo-electrocatalytic, or electrocatalytic water splitting. This work provides insightful guidance to advanced nanocatalysis based on twisted layered materials.

Computational discovery of PtS2/GaSe van der Waals heterostructure for solar energy applications

2D van der Waals (vdW) heterostructures as potential materials for solar energy-related applications have been brought to the forefront for researchers. Here, by employing first-principles calculations, we proposed that the PtS₂/GaSe vdW heterostructure is a distinguished candidate for photocatalytic water splitting and solar cells. It is shown that the PtS₂/GaSe heterostructure exhibits high thermal stability with an indirect band gap of 1.81 eV. We further highlighted the strain induced type-V to type-II band alignment transitions and band gap variations in PtS₂/GaSe heterostructures. More importantly, the outstanding absorption coefficients in the visible light region and high carrier mobility further guarantee the photo energy conversion efficiency of PtS₂/GaSe heterostructures. Interestingly, the natural type-V band alignments of PtS₂/GaSe heterostructures are appropriate for the redox potential of water. On the other hand, the power conversion efficiency of ZnO/(PtS₂/GaSe heterostructure)/CIGS (copper indium gallium diselenide) solar cells can achieve ∼17.4%, which can be further optimized up to ∼18.5% by increasing the CIGS thickness. Our present study paves the way for facilitating the potential application of vdW heterostructures as a promising photocatalyst for water splitting as well as the buffer layer for solar cells.

Concentric Approximation for Fast and Accurate Numerical Evaluation of Nonadiabatic Coupling with Projector Augmented-Wave Pseudopotentials

We develop an efficient and accurate method for numerical evaluation of nonadiabatic (NA) coupling in the Kohn-Sham representation with projector augmented-wave (PAW) pseudopotentials that are commonly used in electronic structure calculations on nanoscale, condensed matter, and molecular systems. Without additional cost, the method provides an order of magnitude improvement in accuracy compared to the current technique, while it is 3-4 orders of magnitude faster than the exact evaluation. Atomic displacements over typical time steps in molecular dynamics (MD) simulations are much smaller than the size of the PAW core region, and therefore, evaluation of the NA in the core is simplified. The accuracy is demonstrated with three condensed matter systems. The method is robust to variation in the MD time step. The accurate NA coupling evaluation also helps in maintaining phase-consistency of the NA coupling and identifying trivial crossings of adiabatic states. The approach stimulates NAMD applications to modeling of modern materials and processes.

Crystal Symmetry and Static Electron Correlation Greatly Accelerate Nonradiative Dynamics in Lead Halide Perovskites

Using a recently developed many-body nonadiabatic molecular dynamics (NA-MD) framework for large condensed matter systems, we study the phonon-driven nonradiative relaxation of excess electronic excitation energy in cubic and tetragonal phases of the lead halide perovskite CsPbI₃. We find that the many-body treatment of the electronic excited states significantly changes the structure of the excited states' coupling, promotes a stronger nonadiabatic coupling of states, and ultimately accelerates the relaxation dynamics relative to the single-particle description of excited states. The acceleration of the nonadiabatic dynamics correlates with the degree of configurational mixing, which is controlled by the crystal symmetry. The higher-symmetry cubic phase of CsPbI₃ exhibits stronger configuration mixing than does the tetragonal phase and subsequently yields faster nonradiative dynamics. Overall, using a many-body treatment of excited states and accounting for decoherence dynamics are important for closing the gap between the computationally derived and experimentally measured nonradiative excitation energy relaxation rates.