Pub Date : 2024-10-16DOI: 10.1021/acs.jpclett.4c02016
Rihards Aleksis, Elton T. Montrazi, Lucio Frydman
NMR finds a wide range of applications, ranging from fundamental chemistry to medical imaging. The technique, however, has an inherently low signal-to-noise ratio (SNR)─particularly when dealing with nuclei having low natural abundances and/or low γs. In these cases, sensitivity is often enhanced by methods that, similar to INEPT, transfer polarization from neighboring <sup>1</sup>Hs via <i>J</i>-couplings. In 1958, Carr proposed an alternative approach to increase NMR sensitivity, which involves generating and continuously detecting a steady-state transverse magnetization, by applying a train of pulses on an ensemble of noninteracting spins. This study broadens Carr’s steady-state free precession (SSFP) framework to encompass the possibility of adding onto it coherent polarization transfers, allowing one to combine the SNR-enhancing benefits of both INEPT and SSFP into a single experiment. Herein, the derivation of the ensuing INEPT-SSFP (ISSFP) sequences is reported. Their use in <sup>13</sup>C NMR and MRI experiments leads to ca. 300% improvements in SNR/ <i></i><span style="color: inherit;"></span><span data-mathml='<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><msqrt><mrow><mi mathvariant="normal">unit time</mi></mrow></msqrt></math>' role="presentation" style="position: relative;" tabindex="0"><nobr aria-hidden="true"><span overflow="scroll" style="width: 5.003em; display: inline-block;"><span style="display: inline-block; position: relative; width: 4.548em; height: 0px; font-size: 110%;"><span style="position: absolute; clip: rect(1.026em, 1004.55em, 2.616em, -999.997em); top: -2.156em; left: 0em;"><span><span><span style="display: inline-block; position: relative; width: 4.548em; height: 0px;"><span style="position: absolute; clip: rect(3.128em, 1003.58em, 4.151em, -999.997em); top: -3.974em; left: 0.912em;"><span><span><span style="font-family: STIXMathJax_Main;">unit time</span></span></span><span style="display: inline-block; width: 0px; height: 3.98em;"></span></span><span style="position: absolute; clip: rect(3.526em, 1003.64em, 3.923em, -999.997em); top: -4.656em; left: 0.912em;"><span style="display: inline-block; position: relative; width: 3.639em; height: 0px;"><span style="position: absolute; font-family: STIXMathJax_Symbols; top: -3.974em; left: 0em;">⎯<span style="display: inline-block; width: 0px; height: 3.98em;"></span></span><span style="position: absolute; font-family: STIXMathJax_Symbols; top: -3.974em; left: 3.298em;">⎯<span style="display: inline-block; width: 0px; height: 3.98em;"></span></span><span style="font-family: STIXMathJax_Symbols; position: absolute; top: -3.974em; left: 0.23em;">⎯<span style="display: inline-block; width: 0px; height: 3.98em;"></span></span><span style="font-family: STIXMathJax_Symbols; position: absolute; top: -3.974em; left: 0.514em;">⎯<span style="display: inline-block; width: 0px; height: 3.98em;"></sp
{"title":"Heteronuclear Polarization Transfer under Steady-State Conditions: The INEPT-SSFP Experiment","authors":"Rihards Aleksis, Elton T. Montrazi, Lucio Frydman","doi":"10.1021/acs.jpclett.4c02016","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02016","url":null,"abstract":"NMR finds a wide range of applications, ranging from fundamental chemistry to medical imaging. The technique, however, has an inherently low signal-to-noise ratio (SNR)─particularly when dealing with nuclei having low natural abundances and/or low γs. In these cases, sensitivity is often enhanced by methods that, similar to INEPT, transfer polarization from neighboring <sup>1</sup>Hs via <i>J</i>-couplings. In 1958, Carr proposed an alternative approach to increase NMR sensitivity, which involves generating and continuously detecting a steady-state transverse magnetization, by applying a train of pulses on an ensemble of noninteracting spins. This study broadens Carr’s steady-state free precession (SSFP) framework to encompass the possibility of adding onto it coherent polarization transfers, allowing one to combine the SNR-enhancing benefits of both INEPT and SSFP into a single experiment. Herein, the derivation of the ensuing INEPT-SSFP (ISSFP) sequences is reported. Their use in <sup>13</sup>C NMR and MRI experiments leads to ca. 300% improvements in SNR/ <i></i><span style=\"color: inherit;\"></span><span data-mathml='<math xmlns=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\" overflow=\"scroll\"><msqrt><mrow><mi mathvariant=\"normal\">unit time</mi></mrow></msqrt></math>' role=\"presentation\" style=\"position: relative;\" tabindex=\"0\"><nobr aria-hidden=\"true\"><span overflow=\"scroll\" style=\"width: 5.003em; display: inline-block;\"><span style=\"display: inline-block; position: relative; width: 4.548em; height: 0px; font-size: 110%;\"><span style=\"position: absolute; clip: rect(1.026em, 1004.55em, 2.616em, -999.997em); top: -2.156em; left: 0em;\"><span><span><span style=\"display: inline-block; position: relative; width: 4.548em; height: 0px;\"><span style=\"position: absolute; clip: rect(3.128em, 1003.58em, 4.151em, -999.997em); top: -3.974em; left: 0.912em;\"><span><span><span style=\"font-family: STIXMathJax_Main;\">unit time</span></span></span><span style=\"display: inline-block; width: 0px; height: 3.98em;\"></span></span><span style=\"position: absolute; clip: rect(3.526em, 1003.64em, 3.923em, -999.997em); top: -4.656em; left: 0.912em;\"><span style=\"display: inline-block; position: relative; width: 3.639em; height: 0px;\"><span style=\"position: absolute; font-family: STIXMathJax_Symbols; top: -3.974em; left: 0em;\">⎯<span style=\"display: inline-block; width: 0px; height: 3.98em;\"></span></span><span style=\"position: absolute; font-family: STIXMathJax_Symbols; top: -3.974em; left: 3.298em;\">⎯<span style=\"display: inline-block; width: 0px; height: 3.98em;\"></span></span><span style=\"font-family: STIXMathJax_Symbols; position: absolute; top: -3.974em; left: 0.23em;\">⎯<span style=\"display: inline-block; width: 0px; height: 3.98em;\"></span></span><span style=\"font-family: STIXMathJax_Symbols; position: absolute; top: -3.974em; left: 0.514em;\">⎯<span style=\"display: inline-block; width: 0px; height: 3.98em;\"></sp","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The atomic configurations and concentrations of intrinsic defects profoundly influence the electrical and optical properties of the semiconductor materials. This influence is particularly significant in the case of β-Ga2O3, which is a highly promising ultrawide bandgap semiconductor characterized by highly complex intrinsic defect configurations. Despite its importance, there is a notable absence of an accurate method to recognize these defects in large-scale atomistic computational modeling. We design an effective algorithm for the explicit identification of various intrinsic point defects in the β-Ga2O3 lattice, which constitutes the integration of the particle swarm optimization (PSO) and K-means clustering (K-MC) methods. Our algorithm attains the recognition accuracy exceeding 95%. Finally, the algorithm is applied to dynamic simulations, where the feasibility of dynamic real-time detection is explored.
{"title":"A Radial Distribution Function Based Recognition Algorithm of Point Defects in Large-Scale β-Ga2O3 Systems","authors":"Mengzhi Yan, Junlei Zhao, Jesper Byggmästar, Flyura Djurabekova, Zongwei Xu","doi":"10.1021/acs.jpclett.4c02469","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02469","url":null,"abstract":"The atomic configurations and concentrations of intrinsic defects profoundly influence the electrical and optical properties of the semiconductor materials. This influence is particularly significant in the case of β-Ga<sub>2</sub>O<sub>3</sub>, which is a highly promising ultrawide bandgap semiconductor characterized by highly complex intrinsic defect configurations. Despite its importance, there is a notable absence of an accurate method to recognize these defects in large-scale atomistic computational modeling. We design an effective algorithm for the explicit identification of various intrinsic point defects in the β-Ga<sub>2</sub>O<sub>3</sub> lattice, which constitutes the integration of the particle swarm optimization (PSO) and K-means clustering (K-MC) methods. Our algorithm attains the recognition accuracy exceeding 95%. Finally, the algorithm is applied to dynamic simulations, where the feasibility of dynamic real-time detection is explored.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440712","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Complicated phase transitions were observed in a single-component 1-decyl-3-methylimidazolium nitrate ([C10mim][NO3]) ionic liquid (IL) using Raman spectroscopy and synchrotron small- and wide-angle X-ray scattering (SWAXS). Time-resolved synchrotron SWAXS could distinguish the phase transitions depending upon the cooling rate. Low-Q peaks representing a few kinds of layered structures were decomposed. Multiphase coexistence was observed in [C10mim][NO3] at specific cooling rates (8–9 K/min). Ionic liquid crystals (ILCs), hybrid-layered crystals, and hexagonal close-packed structures coexisted simultaneously. At the cooling rate region, the reentrant phase transition of the ILC phase upon heating was observed.
{"title":"Multiphase Coexistence in an Ionic Liquid: 1-Decyl-3-methylimidazolium Nitrate","authors":"Hiroshi Abe, Shusei Maruyama, Hiroaki Kishimura, Mikio Uruichi, Daisuke Okuyama, Hajime Sagayama","doi":"10.1021/acs.jpclett.4c02716","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02716","url":null,"abstract":"Complicated phase transitions were observed in a single-component 1-decyl-3-methylimidazolium nitrate ([C<sub>10</sub>mim][NO<sub>3</sub>]) ionic liquid (IL) using Raman spectroscopy and synchrotron small- and wide-angle X-ray scattering (SWAXS). Time-resolved synchrotron SWAXS could distinguish the phase transitions depending upon the cooling rate. Low-<i>Q</i> peaks representing a few kinds of layered structures were decomposed. Multiphase coexistence was observed in [C<sub>10</sub>mim][NO<sub>3</sub>] at specific cooling rates (8–9 K/min). Ionic liquid crystals (ILCs), hybrid-layered crystals, and hexagonal close-packed structures coexisted simultaneously. At the cooling rate region, the reentrant phase transition of the ILC phase upon heating was observed.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440725","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carbon-based catalysts hold significant promise for photocatalytic hydrogen evolution. A critical challenge lies in optimizing the balance between electron longevity and its accumulation to avoid bottlenecks in photocatalytic efficiency. In this study, we introduce an innovative and efficient strategy for the rapid extraction (<100 fs) of photoinduced free electrons from a carbon-based catalyst without forming additional metal-based heterojunction hybrids. This method effectively prevents excessive accumulation of free carriers within the catalyst. The rapidly extracted electrons are then utilized for photocatalytic hydrogen production, resulting in a 10-fold increase in activity compared to the pristine catalyst, with platinum (3 wt%) used as a cocatalyst. Our strategy significantly enhances the performance of a state-of-the-art catalyst, offering a clean and cost-effective method for producing clean energy. This work demonstrates how a fundamental understanding of molecular-level phenomena and their optimization can pave the way for delivering clean and affordable energy to society.
{"title":"Role of Trap Optimization in a Heterostructure Carbon Nitride as a Methodology to Enhance Photocatalytic Hydrogen Production","authors":"Soumyadeep Saha, Ramesh Mandal, Sadashiv Wadepalli, Prakriti Ranjan Bangal, Santanu Bhattacharyya","doi":"10.1021/acs.jpclett.4c02556","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02556","url":null,"abstract":"Carbon-based catalysts hold significant promise for photocatalytic hydrogen evolution. A critical challenge lies in optimizing the balance between electron longevity and its accumulation to avoid bottlenecks in photocatalytic efficiency. In this study, we introduce an innovative and efficient strategy for the rapid extraction (<100 fs) of photoinduced free electrons from a carbon-based catalyst without forming additional metal-based heterojunction hybrids. This method effectively prevents excessive accumulation of free carriers within the catalyst. The rapidly extracted electrons are then utilized for photocatalytic hydrogen production, resulting in a 10-fold increase in activity compared to the pristine catalyst, with platinum (3 wt%) used as a cocatalyst. Our strategy significantly enhances the performance of a state-of-the-art catalyst, offering a clean and cost-effective method for producing clean energy. This work demonstrates how a fundamental understanding of molecular-level phenomena and their optimization can pave the way for delivering clean and affordable energy to society.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440724","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-16DOI: 10.1021/acs.jpclett.4c02345
Fraser J. Angus, Wai Kin Yiu, Hongbo Mo, Tik Lun Leung, Muhammad Umair Ali, Yin Li, Jingbo Wang, Anita. W. Y. Ho-Baillie, Graeme Cooke, Aleksandra B. Djurišić, Pablo Docampo
Completing the picture of the underlying physics of perovskite solar cell interfaces that incorporate self-assembled molecular layers (SAMs) will accelerate further progress in p-i-n devices. In this work, we modified the Fermi level of a nickel oxide–perovskite interface by utilizing SAM layers with a range of dipole strengths to establish the link between the resulting shift of the built-in potential of the solar cell and the device parameters. To achieve this, we fabricated a series of high-efficiency perovskite solar cells with no hysteresis and characterized them through stabilize and pulse (SaP), JV curve, and time-resolved photoluminescence (TRPL) measurements. Our results unambiguously show that the potential drop across the perovskite layer (in the range of 0.6–1 V) exceeds the work function difference at the device’s electrodes. These extracted potential drop values directly correlate to work function differences in the adjacent transport layers, thus demonstrating that their Fermi level difference entirely drives the built-in potential in this device configuration. Additionally, we find that selecting a SAM with a deep HOMO level can result in charge accumulation at the interface, leading to reduced current flow. Our findings provide insights into the device physics of p-i-n perovskite solar cells, highlighting the importance of interfacial energetics on device performance.
完善包含自组装分子层（SAM）的包晶太阳能电池界面的基本物理学原理，将加速 pi-n 器件的进一步发展。在这项研究中，我们利用具有不同偶极子强度的 SAM 层改变了氧化镍-透辉石界面的费米级，从而建立了太阳能电池内置电势的变化与器件参数之间的联系。为此，我们制造了一系列无滞后的高效率过氧化物太阳能电池，并通过稳定和脉冲（SaP）、JV 曲线和时间分辨光致发光（TRPL）测量对其进行了表征。我们的研究结果明确显示，过氧化物层上的电位差（范围在 0.6-1 V 之间）超过了器件电极上的功函数差。这些提取的电位降值与相邻传输层的功函数差直接相关，从而证明它们的费米级差完全驱动了该器件配置中的内置电位。此外，我们还发现，选择具有较深 HOMO 水平的 SAM 会导致电荷在界面处积累，从而降低电流。我们的研究结果为 pi-i-n 包晶太阳能电池的器件物理学提供了见解，突出了界面能量学对器件性能的重要性。
{"title":"Understanding the Impact of SAM Fermi Levels on High Efficiency p-i-n Perovskite Solar Cells","authors":"Fraser J. Angus, Wai Kin Yiu, Hongbo Mo, Tik Lun Leung, Muhammad Umair Ali, Yin Li, Jingbo Wang, Anita. W. Y. Ho-Baillie, Graeme Cooke, Aleksandra B. Djurišić, Pablo Docampo","doi":"10.1021/acs.jpclett.4c02345","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02345","url":null,"abstract":"Completing the picture of the underlying physics of perovskite solar cell interfaces that incorporate self-assembled molecular layers (SAMs) will accelerate further progress in p-i-n devices. In this work, we modified the Fermi level of a nickel oxide–perovskite interface by utilizing SAM layers with a range of dipole strengths to establish the link between the resulting shift of the built-in potential of the solar cell and the device parameters. To achieve this, we fabricated a series of high-efficiency perovskite solar cells with no hysteresis and characterized them through stabilize and pulse (SaP), JV curve, and time-resolved photoluminescence (TRPL) measurements. Our results unambiguously show that the potential drop across the perovskite layer (in the range of 0.6–1 V) exceeds the work function difference at the device’s electrodes. These extracted potential drop values directly correlate to work function differences in the adjacent transport layers, thus demonstrating that their Fermi level difference entirely drives the built-in potential in this device configuration. Additionally, we find that selecting a SAM with a deep HOMO level can result in charge accumulation at the interface, leading to reduced current flow. Our findings provide insights into the device physics of p-i-n perovskite solar cells, highlighting the importance of interfacial energetics on device performance.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142440718","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-15DOI: 10.1021/acs.jpclett.4c02503
Sebastian V. Pios, Jiaji Zhang, Maxim F. Gelin, Hong-Guang Duan, Lipeng Chen
The development of X-ray free-electron lasers has enabled ultrafast X-ray diffraction (XRD) experiments, which are capable of resolving electronic and vibrational transitions and structural changes in molecules or capturing molecular movies. While time-resolved XRD has attracted more attention, the extraction of information from signals is challenging and requires theoretical support. In this work, we combined X-ray scattering theory and a trajectory surface hopping approach to resolve dynamical changes in the electronic structure of photoexcited molecules by studying the time evolution of electron density changes between electronic excited states and ground state. Using the pyrazine molecule as an example, we show that key features of reaction pathways can be identified, enabling the capture of structural changes associated with electronic transitions for a photoexcited molecule.
X 射线自由电子激光器的发展使得超快 X 射线衍射（XRD）实验成为可能，它能够解析分子中的电子和振动跃迁以及结构变化，或捕捉分子电影。虽然时间分辨 XRD 引起了越来越多的关注，但从信号中提取信息是一项挑战，需要理论支持。在这项工作中，我们结合了 X 射线散射理论和轨迹表面跳跃方法，通过研究电子激发态和基态之间电子密度变化的时间演化，解析了光激发分子电子结构的动态变化。以吡嗪分子为例，我们表明可以识别反应路径的关键特征，从而捕捉光激发分子与电子跃迁相关的结构变化。
{"title":"Tracking the Electron Density Changes in Excited States: A Computational Study of Pyrazine","authors":"Sebastian V. Pios, Jiaji Zhang, Maxim F. Gelin, Hong-Guang Duan, Lipeng Chen","doi":"10.1021/acs.jpclett.4c02503","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02503","url":null,"abstract":"The development of X-ray free-electron lasers has enabled ultrafast X-ray diffraction (XRD) experiments, which are capable of resolving electronic and vibrational transitions and structural changes in molecules or capturing molecular movies. While time-resolved XRD has attracted more attention, the extraction of information from signals is challenging and requires theoretical support. In this work, we combined X-ray scattering theory and a trajectory surface hopping approach to resolve dynamical changes in the electronic structure of photoexcited molecules by studying the time evolution of electron density changes between electronic excited states and ground state. Using the pyrazine molecule as an example, we show that key features of reaction pathways can be identified, enabling the capture of structural changes associated with electronic transitions for a photoexcited molecule.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142436470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-15DOI: 10.1021/acs.jpclett.4c02549
Jiří Janoš, Petr Slavíček, Basile F. E. Curchod
Over the last decades, theoretical photochemistry has produced multiple techniques to simulate the nonadiabatic dynamics of molecules. Surprisingly, much less effort has been devoted to adequately describing the first step of a photochemical or photophysical process: photoexcitation. Here, we propose a formalism to include the effect of a laser pulse in trajectory-based nonadiabatic dynamics at the level of the initial conditions, with no additional cost. The promoted density approach (PDA) decouples the excitation from the nonadiabatic dynamics by defining a new set of initial conditions, which include an excitation time. PDA with surface hopping leads to nonadiabatic dynamics simulations in excellent agreement with quantum dynamics using an explicit laser pulse and highlights the strong impact of a laser pulse on the resulting photodynamics and the limits of the (sudden) vertical excitation. Combining PDA with trajectory-based nonadiabatic methods is possible for any arbitrary-sized molecules using a code provided in this work.
{"title":"Including Photoexcitation Explicitly in Trajectory-Based Nonadiabatic Dynamics at No Cost","authors":"Jiří Janoš, Petr Slavíček, Basile F. E. Curchod","doi":"10.1021/acs.jpclett.4c02549","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02549","url":null,"abstract":"Over the last decades, theoretical photochemistry has produced multiple techniques to simulate the nonadiabatic dynamics of molecules. Surprisingly, much less effort has been devoted to adequately describing the first step of a photochemical or photophysical process: photoexcitation. Here, we propose a formalism to include the effect of a laser pulse in trajectory-based nonadiabatic dynamics at the level of the initial conditions, with no additional cost. The promoted density approach (PDA) decouples the excitation from the nonadiabatic dynamics by defining a new set of initial conditions, which include an excitation time. PDA with surface hopping leads to nonadiabatic dynamics simulations in excellent agreement with quantum dynamics using an explicit laser pulse and highlights the strong impact of a laser pulse on the resulting photodynamics and the limits of the (sudden) vertical excitation. Combining PDA with trajectory-based nonadiabatic methods is possible for any arbitrary-sized molecules using a code provided in this work.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142436472","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-15DOI: 10.1021/acs.jpclett.4c02653
Nikolay V. Tkachenko, Linus Bjarne Dittmer, Rebecca Tomann, Martin Head-Gordon
The addition of dispersion corrections to density functionals is essential for accurate energy and geometry predictions. Among them, the D4 scheme is popular due to its low computational cost and high accuracy. However, due to its design, the D4 correction can occasionally lead to anomalies, such as unphysical curvature and bumps in the potential energy surface. We find these anomalies are common in the D4 model, although observable consequences are rarer than in the D3 model for reasons we explain. Nevertheless, we uncover instances of unphysical local minima and stationary points with the D4 scheme and propose two solutions that yield smoother dispersion energy as a function of nuclear position. One is trivial to implement, based on a smoother reparametrization of Gaussian weighting (D4S) to find the effective coordination number. The other replaces Gaussian weighting with soft linear interpolation (D4SL). These new approaches usually remove artificial extremum points, while maintaining accuracy.
{"title":"Smooth Dispersion Is Physically Appropriate: Assessing and Amending the D4 Dispersion Model","authors":"Nikolay V. Tkachenko, Linus Bjarne Dittmer, Rebecca Tomann, Martin Head-Gordon","doi":"10.1021/acs.jpclett.4c02653","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02653","url":null,"abstract":"The addition of dispersion corrections to density functionals is essential for accurate energy and geometry predictions. Among them, the D4 scheme is popular due to its low computational cost and high accuracy. However, due to its design, the D4 correction can occasionally lead to anomalies, such as unphysical curvature and bumps in the potential energy surface. We find these anomalies are common in the D4 model, although observable consequences are rarer than in the D3 model for reasons we explain. Nevertheless, we uncover instances of unphysical local minima and stationary points with the D4 scheme and propose two solutions that yield smoother dispersion energy as a function of nuclear position. One is trivial to implement, based on a smoother reparametrization of Gaussian weighting (D4S) to find the effective coordination number. The other replaces Gaussian weighting with soft linear interpolation (D4SL). These new approaches usually remove artificial extremum points, while maintaining accuracy.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142436390","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-15DOI: 10.1021/acs.jpclett.4c02196
Qiantong Meng, Lili Liu, Dandan Song, Shuai Wang, Ruixuan Qin, Gang Fu
In recent years, significant research has been conducted on supported clusters due to their high dispersion, atomic efficiency, and unsaturated coordination, particularly in ammonia synthesis. This study investigates the catalytic performance of flexible iron clusters embedded in two-dimensional carbon–nitrogen materials for ammonia synthesis. Using density functional theory and ab initio molecular dynamics simulations, we demonstrate that the structural flexibility of these clusters significantly enhances their catalytic activity. The flexibility coefficient, derived from the full width at half maximum of the Fe–Fe radial distribution function, is introduced as a novel descriptor for N2 bond cleavage. Our findings reveal that flexible Fe clusters adaptively modify their structures during the reaction process, lowering energy barriers for N2 activation and subsequent hydrogenation. This study opens new avenues for designing advanced catalytic systems based on structural flexibility to meet the growing demand for sustainable and energy-efficient ammonia production.
近年来，人们对具有高分散性、原子效率和不饱和配位性的支撑簇进行了大量研究，尤其是在氨合成方面。本研究探讨了嵌入二维碳氮材料中的柔性铁簇在氨合成中的催化性能。利用密度泛函理论和 ab initio 分子动力学模拟，我们证明了这些铁簇的结构柔性可显著提高其催化活性。根据铁-铁径向分布函数的半最大全宽推导出的柔性系数被引入作为 N2 键裂解的新描述因子。我们的研究结果表明，柔性铁簇在反应过程中会自适应地改变其结构，从而降低 N2 活化和随后氢化的能量障碍。这项研究为设计基于结构灵活性的先进催化系统开辟了新途径，以满足对可持续和高能效合成氨生产日益增长的需求。
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Contrary to the common assumption that a higher bulk content of precious metals facilitates the preservation of more surface noble metal by serving as a reservoir for surface enrichment, we demonstrate that a lower bulk content of Au results in a more stable arrangement of Au atoms at the surface of Cu–Au nanoparticles when exposed to an O2 atmosphere. Using ambient pressure X-ray photoelectron spectroscopy, we investigate the surface segregation and oxidation behavior of Cu–Au nanoparticles across various compositions. Our results reveal that in Au-rich nanoparticles exposed to an H2 atmosphere, surface segregation prompts the formation of a continuous Au-enriched shell, which subsequently oxidizes into a complete CuOx shell upon transitioning to an O2 atmosphere. Conversely, in Au-poor nanoparticles during H2 treatment, segregation results in the emergence of Au clusters embedded within the surface layer, persisting upon exposure to O2. This unexpected phenomenon shows that reducing the bulk content of precious metals can enhance the surface stability of noble atoms under oxidizing conditions, as further demonstrated by comparing the catalytic performance of Cu–Au nanoparticles with varying Au bulk contents in CO oxidation.
一般认为，贵金属的体积含量越高，表面富集的惰性金属就越多，与此相反，我们证明，金的体积含量越低，暴露在氧气环境中时，金原子在铜金纳米粒子表面的排列就越稳定。利用常压 X 射线光电子能谱，我们研究了不同成分的铜金纳米粒子的表面偏析和氧化行为。我们的研究结果表明，在富含金的纳米粒子中，暴露在 H2 大气中，表面偏析会促使形成连续的富金外壳，随后在过渡到 O2 大气时，外壳会氧化成完整的铜氧化物。相反，在 H2 处理过程中，贫金纳米粒子中的偏析会导致嵌入表层的金簇出现，并在暴露于 O2 时持续存在。这一意想不到的现象表明，降低贵金属的体积含量可以增强氧化条件下惰性原子的表面稳定性，比较不同金体积含量的铜金纳米粒子在 CO 氧化中的催化性能也进一步证明了这一点。
{"title":"Enhancing Stability of Surface Au under Oxidizing Conditions through Reduced Bulk Au Content","authors":"Jianyu Wang, Xiaobo Chen, Chaoran Li, Yaguang Zhu, Jing Li, Shiyao Shan, Yupeng Wu, Adrian Hunt, Iradwikanari Waluyo, J. Anibal Boscoboinik, Xiao Tong, Chuan-Jian Zhong, Guangwen Zhou","doi":"10.1021/acs.jpclett.4c02172","DOIUrl":"https://doi.org/10.1021/acs.jpclett.4c02172","url":null,"abstract":"Contrary to the common assumption that a higher bulk content of precious metals facilitates the preservation of more surface noble metal by serving as a reservoir for surface enrichment, we demonstrate that a lower bulk content of Au results in a more stable arrangement of Au atoms at the surface of Cu–Au nanoparticles when exposed to an O<sub>2</sub> atmosphere. Using ambient pressure X-ray photoelectron spectroscopy, we investigate the surface segregation and oxidation behavior of Cu–Au nanoparticles across various compositions. Our results reveal that in Au-rich nanoparticles exposed to an H<sub>2</sub> atmosphere, surface segregation prompts the formation of a continuous Au-enriched shell, which subsequently oxidizes into a complete CuO<sub><i>x</i></sub> shell upon transitioning to an O<sub>2</sub> atmosphere. Conversely, in Au-poor nanoparticles during H<sub>2</sub> treatment, segregation results in the emergence of Au clusters embedded within the surface layer, persisting upon exposure to O<sub>2</sub>. This unexpected phenomenon shows that reducing the bulk content of precious metals can enhance the surface stability of noble atoms under oxidizing conditions, as further demonstrated by comparing the catalytic performance of Cu–Au nanoparticles with varying Au bulk contents in CO oxidation.","PeriodicalId":62,"journal":{"name":"The Journal of Physical Chemistry Letters","volume":null,"pages":null},"PeriodicalIF":6.475,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142436468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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