Lixue Cheng, P. Bernát Szabó, Zeno Schätzle, Derk Kooi, Jonas Köhler, Klaas J. H. Giesbertz, Frank Noé, Jan Hermann, Paola Gori-Giorgi, Adam Foster
Variational ab-initio methods in quantum chemistry stand out among other methods in providing direct access to the wave function. This allows in principle straightforward extraction of any other observable of interest, besides the energy, but in practice this extraction is often technically difficult and computationally impractical. Here, we consider the electron density as a central observable in quantum chemistry and introduce a novel method to obtain accurate densities from real-space many-electron wave functions by representing the density with a neural network that captures known asymptotic properties and is trained from the wave function by score matching and noise-contrastive estimation. We use variational quantum Monte Carlo with deep-learning ans"atze (deep QMC) to obtain highly accurate wave functions free of basis set errors, and from them, using our novel method, correspondingly accurate electron densities, which we demonstrate by calculating dipole moments, nuclear forces, contact densities, and other density-based properties.
{"title":"Highly Accurate Real-space Electron Densities with Neural Networks","authors":"Lixue Cheng, P. Bernát Szabó, Zeno Schätzle, Derk Kooi, Jonas Köhler, Klaas J. H. Giesbertz, Frank Noé, Jan Hermann, Paola Gori-Giorgi, Adam Foster","doi":"arxiv-2409.01306","DOIUrl":"https://doi.org/arxiv-2409.01306","url":null,"abstract":"Variational ab-initio methods in quantum chemistry stand out among other\u0000methods in providing direct access to the wave function. This allows in\u0000principle straightforward extraction of any other observable of interest,\u0000besides the energy, but in practice this extraction is often technically\u0000difficult and computationally impractical. Here, we consider the electron\u0000density as a central observable in quantum chemistry and introduce a novel\u0000method to obtain accurate densities from real-space many-electron wave\u0000functions by representing the density with a neural network that captures known\u0000asymptotic properties and is trained from the wave function by score matching\u0000and noise-contrastive estimation. We use variational quantum Monte Carlo with\u0000deep-learning ans\"atze (deep QMC) to obtain highly accurate wave functions\u0000free of basis set errors, and from them, using our novel method,\u0000correspondingly accurate electron densities, which we demonstrate by\u0000calculating dipole moments, nuclear forces, contact densities, and other\u0000density-based properties.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"76 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper derives and demonstrates a new, purely density-based ab initio approach for calculation of the energies and properties of many-electron systems. It is based upon the discovery of relationships that govern the "mechanics" of the electron density -- i.e., relations that connect its behaviors at different points in space. Unlike wave mechanics or prior electron-density-based implementations, such as DFT, this density-mechanical implementation of quantum mechanics involves no many-electron or one-electron wave functions (i.e., orbitals). Thus, there is no need to calculate exchange energies, because there are no orbitals to permute or "exchange" within two-electron integrals used to calculate electron-electron repulsion energies. In practice, exchange does not exist within quantum density mechanics. In fact, no two-electron integrals need be calculated at all, beyond a single coulomb integral for the 2-electron system. Instead, a "radius expansion method" is introduced that permits determination of the two-electron interaction for an N-electron system from one with (N-1)-electrons. Also, the method does not rely upon a Schrodinger-like equation or the variational method for determination of accurate energies and densities. Rather, the above-described results follow from the derivation and solution of a "governing equation" for each number of electrons to obtain a screening relation that connects the behavior at the "tail" of a one-electron density, to that at the Bohr radius. Solution of these equations produces simple expressions that deliver a total energy for a 2-electron atom that is nearly identical to the experimental value, plus accurate energies for neutral 3, 4, and 5-electron atoms, along with accurate one-electron densities of these atoms. Further, these methods scale in complexity only as N, not as a power of N, as do most other accurate many-electron methods.
这篇论文推导并演示了一种新的、纯粹基于密度的 ab initio 方法，用于计算多电子系统的能量和性质。该方法基于对电子密度 "力学 "关系的发现，即在空间不同点上连接电子密度行为的关系。与波动力学或基于前电子密度的实现（如 DFT）不同，量子力学的这种密度力学实现不涉及多电子或单电子波函数（即轨道）。因此，不需要计算交换能，因为在用于计算电子-电子斥力能的双电子积分中，没有轨道可以排列或 "交换"。实际上，除了计算双电子系统的单一库仑积分之外，根本不需要计算双电子积分。取而代之的是一种 "半径扩展法"，它允许从一个有（N-1）个电子的系统中确定一个 N 电子系统的双电子相互作用。此外，该方法并不依赖于类似薛定谔方程或变分法来确定精确的能量和密度。相反，上述结果源于对每个电子数的 "支配方程 "的推导和求解，从而获得一种屏蔽关系，将单电子密度 "尾部 "的行为与玻尔半径的行为联系起来。求解这些方程可以得到简单的表达式，从而得到与实验值几乎相同的 2 电子原子的总能量，以及中性 3、4 和 5 电子原子的精确能量和这些原子的精确单电子密度。此外，这些方法的不复杂度仅以 N 为标度，而不是以 N 的幂为标度，这一点与其他大多数精确的单电子学方法相同。
{"title":"Quantum Density Mechanics: Accurate, purely density-based textit{ab initio} implementation of many-electron quantum mechanics","authors":"James C. Ellenbogen","doi":"arxiv-2409.00586","DOIUrl":"https://doi.org/arxiv-2409.00586","url":null,"abstract":"This paper derives and demonstrates a new, purely density-based ab initio\u0000approach for calculation of the energies and properties of many-electron\u0000systems. It is based upon the discovery of relationships that govern the\u0000\"mechanics\" of the electron density -- i.e., relations that connect its\u0000behaviors at different points in space. Unlike wave mechanics or prior\u0000electron-density-based implementations, such as DFT, this density-mechanical\u0000implementation of quantum mechanics involves no many-electron or one-electron\u0000wave functions (i.e., orbitals). Thus, there is no need to calculate exchange\u0000energies, because there are no orbitals to permute or \"exchange\" within\u0000two-electron integrals used to calculate electron-electron repulsion energies.\u0000In practice, exchange does not exist within quantum density mechanics. In fact,\u0000no two-electron integrals need be calculated at all, beyond a single coulomb\u0000integral for the 2-electron system. Instead, a \"radius expansion method\" is\u0000introduced that permits determination of the two-electron interaction for an\u0000N-electron system from one with (N-1)-electrons. Also, the method does not rely\u0000upon a Schrodinger-like equation or the variational method for determination of\u0000accurate energies and densities. Rather, the above-described results follow\u0000from the derivation and solution of a \"governing equation\" for each number of\u0000electrons to obtain a screening relation that connects the behavior at the\u0000\"tail\" of a one-electron density, to that at the Bohr radius. Solution of these\u0000equations produces simple expressions that deliver a total energy for a\u00002-electron atom that is nearly identical to the experimental value, plus\u0000accurate energies for neutral 3, 4, and 5-electron atoms, along with accurate\u0000one-electron densities of these atoms. Further, these methods scale in\u0000complexity only as N, not as a power of N, as do most other accurate\u0000many-electron methods.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yu Su, Yao Wang, Zi-Fan Zhu, Yuan Kong, Rui-Xue Xu, YiJing Yan, Xiao Zheng
Graphene has garnered significant attention due to its unique properties. Among its many intriguing characteristics, the tuning effects induced by adsorbed atoms (adatoms) provide immense potential for the design of graphene-based electronic devices. This work explores the electronic migration in the adatom-graphene composite, using the extended dissipaton-equation-of-motion (DEOM) approach. As an exact dynamics theory for open quantum systems embedded in environments composed of non-interacting electrons, the extended DEOM is capable of handling both linear and quadratic environmental couplings (a certain non-Gaussian effect) which account for the interactions between the adatom and the graphene substrate. We demonstrate and analyze the adatom-graphene correlated properties and the tuning effects by simulating the adatom spectral functions with varied Coulomb repulsion strengths. This work offers not only advanced theoretical methods but also new insights into the theoretical investigation of complex functional materials such as graphene-based electronic devices.
{"title":"Extended dissipaton-equation-of-motion approach to study the electronic migration in adatom-graphene composite","authors":"Yu Su, Yao Wang, Zi-Fan Zhu, Yuan Kong, Rui-Xue Xu, YiJing Yan, Xiao Zheng","doi":"arxiv-2409.00669","DOIUrl":"https://doi.org/arxiv-2409.00669","url":null,"abstract":"Graphene has garnered significant attention due to its unique properties.\u0000Among its many intriguing characteristics, the tuning effects induced by\u0000adsorbed atoms (adatoms) provide immense potential for the design of\u0000graphene-based electronic devices. This work explores the electronic migration\u0000in the adatom-graphene composite, using the extended\u0000dissipaton-equation-of-motion (DEOM) approach. As an exact dynamics theory for\u0000open quantum systems embedded in environments composed of non-interacting\u0000electrons, the extended DEOM is capable of handling both linear and quadratic\u0000environmental couplings (a certain non-Gaussian effect) which account for the\u0000interactions between the adatom and the graphene substrate. We demonstrate and\u0000analyze the adatom-graphene correlated properties and the tuning effects by\u0000simulating the adatom spectral functions with varied Coulomb repulsion\u0000strengths. This work offers not only advanced theoretical methods but also new\u0000insights into the theoretical investigation of complex functional materials\u0000such as graphene-based electronic devices.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"96 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present an implementation of alchemical free energy simulations at the quantum mechanical level by directly interpolating the electronic Hamiltonian. The method is compatible with any level of electronic structure theory and requires only one quantum calculation for each molecular dynamics step in contrast to multiple energy evaluations that would be needed when interpolating the ground-state energies. We demonstrate the correctness and applicability of the technique by computing alchemical free energy changes of gas-phase molecules, with both nuclear and electron creation/annihilation. We also show an initial application to first-principles pKa calculation for solvated molecules where we quantum mechanically annihilate a bonded proton.
{"title":"General Quantum Alchemical Free Energy Simulations via Hamiltonian Interpolation","authors":"Chenghan Li, Xing Zhang, Garnet Kin-Lic Chan","doi":"arxiv-2408.17002","DOIUrl":"https://doi.org/arxiv-2408.17002","url":null,"abstract":"We present an implementation of alchemical free energy simulations at the\u0000quantum mechanical level by directly interpolating the electronic Hamiltonian.\u0000The method is compatible with any level of electronic structure theory and\u0000requires only one quantum calculation for each molecular dynamics step in\u0000contrast to multiple energy evaluations that would be needed when interpolating\u0000the ground-state energies. We demonstrate the correctness and applicability of\u0000the technique by computing alchemical free energy changes of gas-phase\u0000molecules, with both nuclear and electron creation/annihilation. We also show\u0000an initial application to first-principles pKa calculation for solvated\u0000molecules where we quantum mechanically annihilate a bonded proton.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yangyang Song, Ning Zhang, Yibo Lei, Yang Guo, Wenjian Liu
Given a number of datasets for evaluating the performance of single reference methods for the low-lying excited states of closed-shell molecules, a comprehensive dataset for assessing the performance of multireference methods for the low-lying excited states of open-shell systems is still lacking. For this reason, we propose an extension (QUEST#4X) of the radial subset of QUEST#4 [J. Chem. Theory Comput. 2020, 16, 3720] to cover 110 doublet and 39 quartet excited states. Near-exact results obtained by iCIPT2 (iterative configuration interaction with selection and second-order perturbation correction) are taken as benchmark to calibrate SDSCI (static-dynamic-static configuration interaction) and SDSPT2 (static-dynamic-static second-order perturbation theory), which are minimal MRCI and CI-like perturbation theory, respectively. It is found that SDSCI is very close in accuracy to ic-MRCISD (internally contracted multireference configuration interaction with singles and doubles), although its computational cost is just that of one iteration of the latter. Unlike most variants of MRPT2, SDSPT2 treats single and multiple states in the same way, and performs similarly as MS-NEVPT2 (multi-state n-electron valence second-order perturbation theory). These findings put the SDS family of methods (SDSPT2, SDSCI, and iCIPT2, etc.) on a firm basis.
{"title":"QUEST#4X: an extension of QUEST#4 for benchmarking multireference wavefunction methods","authors":"Yangyang Song, Ning Zhang, Yibo Lei, Yang Guo, Wenjian Liu","doi":"arxiv-2409.00302","DOIUrl":"https://doi.org/arxiv-2409.00302","url":null,"abstract":"Given a number of datasets for evaluating the performance of single reference\u0000methods for the low-lying excited states of closed-shell molecules, a\u0000comprehensive dataset for assessing the performance of multireference methods\u0000for the low-lying excited states of open-shell systems is still lacking. For\u0000this reason, we propose an extension (QUEST#4X) of the radial subset of\u0000QUEST#4 [J. Chem. Theory Comput. 2020, 16, 3720] to cover 110 doublet and 39\u0000quartet excited states. Near-exact results obtained by iCIPT2 (iterative\u0000configuration interaction with selection and second-order perturbation\u0000correction) are taken as benchmark to calibrate SDSCI (static-dynamic-static\u0000configuration interaction) and SDSPT2 (static-dynamic-static second-order\u0000perturbation theory), which are minimal MRCI and CI-like perturbation theory,\u0000respectively. It is found that SDSCI is very close in accuracy to ic-MRCISD\u0000(internally contracted multireference configuration interaction with singles\u0000and doubles), although its computational cost is just that of one iteration of\u0000the latter. Unlike most variants of MRPT2, SDSPT2 treats single and multiple\u0000states in the same way, and performs similarly as MS-NEVPT2 (multi-state\u0000n-electron valence second-order perturbation theory). These findings put the\u0000SDS family of methods (SDSPT2, SDSCI, and iCIPT2, etc.) on a firm basis.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"41 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224804","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study introduces a machine learning framework to predict the suitability of ionic liquids with unknown physical properties as propellants for electrospray thrusters based on their molecular structure. We construct a training dataset by labeling ionic liquids as suitable (+1) or unsuitable (-1) for electrospray thrusters based on their density, viscosity, and surface tension. The ionic liquids are represented by their molecular descriptors calculated using the Mordred package. We evaluate four machine learning algorithms: Logistic Regression, Support Vector Machine (SVM), Random Forest, and Extreme Gradient Boosting (XGBoost), with SVM demonstrating superior predictive performance. The SVM predicts 193 candidate propellants from a dataset of ionic liquids with unknown physical properties. Further, we employ Shapley Additive Explanations (SHAP) to assess and rank the impact of individual molecular descriptors on model decisions.
{"title":"Propellant Discovery For Electrospray Thrusters Using Machine Learning","authors":"Rafid Bendimerad, Elaine Petro","doi":"arxiv-2408.16951","DOIUrl":"https://doi.org/arxiv-2408.16951","url":null,"abstract":"This study introduces a machine learning framework to predict the suitability\u0000of ionic liquids with unknown physical properties as propellants for\u0000electrospray thrusters based on their molecular structure. We construct a\u0000training dataset by labeling ionic liquids as suitable (+1) or unsuitable (-1)\u0000for electrospray thrusters based on their density, viscosity, and surface\u0000tension. The ionic liquids are represented by their molecular descriptors\u0000calculated using the Mordred package. We evaluate four machine learning\u0000algorithms: Logistic Regression, Support Vector Machine (SVM), Random Forest,\u0000and Extreme Gradient Boosting (XGBoost), with SVM demonstrating superior\u0000predictive performance. The SVM predicts 193 candidate propellants from a\u0000dataset of ionic liquids with unknown physical properties. Further, we employ\u0000Shapley Additive Explanations (SHAP) to assess and rank the impact of\u0000individual molecular descriptors on model decisions.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An adequate understanding of NOx interacting chemistry is a prerequisite for a smoother transition to carbon lean and carbon free fuels such as ammonia and hydrogen. In this regard, this study presents a comprehensive study on the H atom abstraction by NO2 from C3 to C7 alkynes and dienes forming 3 HNO2 isomers (i.e., TRANS HONO, HNO2, and CIS HONO), encompassing 8 hydrocarbons and 24 reactions. Through a combination of high level quantum chemistry computation, the rate coefficients for all studied reactions, over a temperature range from 298 to 2000 K, are computed based on Transition State Theory using the Master Equation System Solver program with considering unsymmetric tunneling corrections. Comprehensive analysis of branching ratios elucidates the diversity and similarities between different species, different HNO2 isomers, and different abstraction sites. Incorporating the calculated rate parameters into a recent chemistry model reveals the significant influences of this type of reaction on model performance, where the updated model is consistently more reactive for all the alkynes and dienes studied in predicting autoignition characteristics. Sensitivity and flux analyses are further conducted, through which the importance of H atom abstractions by NO2 is highlighted. With the updated rate parameters, the branching ratios in fuel consumption clearly shifts towards H atom abstractions by NO2 while away from H atom abstractions by OH. The obtained results emphasize the need for adequately representing these kinetics in new alkyne and diene chemistry models to be developed by using the rate parameters determined in this study, and call for future efforts to experimentally investigate NO2 blending effects on alkynes and dienes.
充分了解氮氧化物的相互作用化学性质是更顺利地过渡到贫碳和无碳燃料（如氨和氢）的先决条件。为此，本研究全面研究了 NO2 从 C3 至 C7 烯烃和二烯中抽取 Hatom 形成 3 种 HNO2 异构体（即 TRANS HONO、HNO2 和 CIS HONO）的过程，包括 8 种碳氢化合物和 24 种反应。通过结合高水平的量子化学计算，以过渡态理论为基础，使用主方程系统求解程序计算了所有研究反应的速率系数，温度范围为 298 至 2000 K，并考虑了非对称隧道校正。对支化率的综合分析阐明了不同物种、不同 HNO2 异构体和不同抽取位点之间的多样性和相似性。将计算出的速率参数纳入最新的化学模型显示了这类反应对模型性能的重大影响，更新后的模型在预测自燃特性时对所有研究的炔烃和二烯烃都具有一致的反应性。进一步进行了灵敏度和通量分析，突出了二氧化氮抽取 H 原子的重要性。随着速率参数的更新，燃料消耗的分支比率明显转向由 NO2 抽取 H 原子，而不是由 OH 抽取 H 原子。所获得的结果强调了利用本研究确定的速率参数在即将开发的新炔烃和二烯烃化学模型中充分反映这些动力学的必要性，并呼吁今后努力通过实验研究二氧化氮对炔烃和二烯烃的掺混效应。
{"title":"On the key kinetic interactions between NOx and unsaturated hydrocarbons: H-atom abstraction from C3-C7 alkynes and dienes by NO2","authors":"Zhengyan Guo, Hongqing Wu, Ruoyue Tang, Xinrui Ren, Ting Zhang, Mingrui Wang, Guojie Liang, Hengjie Guo, Song Cheng","doi":"arxiv-2408.17277","DOIUrl":"https://doi.org/arxiv-2408.17277","url":null,"abstract":"An adequate understanding of NOx interacting chemistry is a prerequisite for\u0000a smoother transition to carbon lean and carbon free fuels such as ammonia and\u0000hydrogen. In this regard, this study presents a comprehensive study on the H\u0000atom abstraction by NO2 from C3 to C7 alkynes and dienes forming 3 HNO2 isomers\u0000(i.e., TRANS HONO, HNO2, and CIS HONO), encompassing 8 hydrocarbons and 24\u0000reactions. Through a combination of high level quantum chemistry computation,\u0000the rate coefficients for all studied reactions, over a temperature range from\u0000298 to 2000 K, are computed based on Transition State Theory using the Master\u0000Equation System Solver program with considering unsymmetric tunneling\u0000corrections. Comprehensive analysis of branching ratios elucidates the\u0000diversity and similarities between different species, different HNO2 isomers,\u0000and different abstraction sites. Incorporating the calculated rate parameters\u0000into a recent chemistry model reveals the significant influences of this type\u0000of reaction on model performance, where the updated model is consistently more\u0000reactive for all the alkynes and dienes studied in predicting autoignition\u0000characteristics. Sensitivity and flux analyses are further conducted, through\u0000which the importance of H atom abstractions by NO2 is highlighted. With the\u0000updated rate parameters, the branching ratios in fuel consumption clearly\u0000shifts towards H atom abstractions by NO2 while away from H atom abstractions\u0000by OH. The obtained results emphasize the need for adequately representing\u0000these kinetics in new alkyne and diene chemistry models to be developed by\u0000using the rate parameters determined in this study, and call for future efforts\u0000to experimentally investigate NO2 blending effects on alkynes and dienes.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224806","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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":"arxiv-2408.17359","DOIUrl":"https://doi.org/arxiv-2408.17359","url":null,"abstract":"Over the last decades, theoretical photochemistry has produced multiple\u0000techniques to simulate the nonadiabatic dynamics of molecules. Surprisingly,\u0000much less effort has been devoted to adequately describing the first step of a\u0000photochemical or photophysical process: photoexcitation. Here, we propose a\u0000formalism to include the effect of a laser pulse in trajectory-based\u0000nonadiabatic dynamics at the level of the initial conditions, with no\u0000additional cost. The promoted density approach (PDA) decouples the excitation\u0000from the nonadiabatic dynamics by defining a new set of initial conditions,\u0000which include an excitation time. PDA with surface hopping leads to\u0000nonadiabatic dynamics simulations in excellent agreement with quantum dynamics\u0000using an explicit laser pulse and highlights the strong impact of a laser pulse\u0000on the resulting photodynamics and the limits of the (sudden) vertical\u0000excitation. Combining PDA with trajectory-based nonadiabatic methods is\u0000possible for any arbitrary-sized molecules using a code provided in this work.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"29 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Haggai Bonneau, Yael Avni, David Andelman, Henri Orland
The response of ionic solutions to time-varying electric fields, quantified by a frequency-dependent conductivity, is essential in many electrochemical applications. Yet, it constitutes a challenging problem due to the combined effect of Coulombic interactions, hydrodynamics, and thermal fluctuations. Here, we study the frequency-dependent conductivity of ionic solutions using a stochastic density functional theory. In the limit of small concentrations, we recover the classical Debye and Falkenhagen (DF) result, predicting an increase in conductivity with field frequency. At higher concentrations, we use a modified Coulomb interaction potential that accounts for the hard-core repulsion between the ions, which was recently employed in the zero-frequency case. Consequently, we extend the DF result to concentrated electrolytes. We discuss experimental and numerical studies and the complexity of observing the DF effect in such setups.
{"title":"Frequency-Dependent Conductivity of Concentrated Electrolytes: A Stochastic Density Functional Theory","authors":"Haggai Bonneau, Yael Avni, David Andelman, Henri Orland","doi":"arxiv-2408.17427","DOIUrl":"https://doi.org/arxiv-2408.17427","url":null,"abstract":"The response of ionic solutions to time-varying electric fields, quantified\u0000by a frequency-dependent conductivity, is essential in many electrochemical\u0000applications. Yet, it constitutes a challenging problem due to the combined\u0000effect of Coulombic interactions, hydrodynamics, and thermal fluctuations.\u0000Here, we study the frequency-dependent conductivity of ionic solutions using a\u0000stochastic density functional theory. In the limit of small concentrations, we\u0000recover the classical Debye and Falkenhagen (DF) result, predicting an increase\u0000in conductivity with field frequency. At higher concentrations, we use a\u0000modified Coulomb interaction potential that accounts for the hard-core\u0000repulsion between the ions, which was recently employed in the zero-frequency\u0000case. Consequently, we extend the DF result to concentrated electrolytes. We\u0000discuss experimental and numerical studies and the complexity of observing the\u0000DF effect in such setups.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Additive manufacturing holds more potential to enable the development of ceramic-based components. Ceramics offer high resistance to heat, high fracture toughness, and are extremely corrosion resistant. Thus, ceramics are widely used in sectors such as the aerospace industry, automotive, microelectronics, and biomedicine. Using various additive manufacturing platforms, ceramics with complex and uniquely designed geometry can be developed to suit specific applications. This project aims at innovating high-temperature thermocouples by embedding conductive metal pastes into a ceramic structure. The paste used includes tungsten, molybdenum, and antimony. The metal pastes are precisely extruded into a T-shaped trench inside the ceramic matrix. Following specific temperature ranges, the ceramic matrix is sintered to improve the properties of the material. The sensors produced can function at extremely high temperatures and are thereby suitable for high-temperature environments. Comparative testing of the 3D sintered sensors with conventional temperature sensors shows high correlation between the two classes of sensors. The resulting R-squared value of 0.9885 is satisfactory which implies the reliability and accuracy of 3D sintering sensors are satisfactory in temperature sensing applications.
快速成型技术在开发陶瓷组件方面具有更大的潜力。陶瓷具有高耐热性、高断裂韧性和极强的耐腐蚀性。因此，陶瓷被广泛应用于航空航天、汽车、微电子和生物医学等领域。利用各种快速成型制造平台，可以开发出具有复杂和独特设计几何形状的陶瓷，以满足特定应用的需要。本项目旨在通过在陶瓷结构中嵌入导电金属浆料来创新高温热电偶。使用的浆料包括钨、钼和锑。金属浆料被精确地挤入陶瓷基体内部的 T 形沟槽中。在特定的温度范围内，陶瓷基体被烧结，以提高材料的性能。生产出的传感器可在极高温度下工作，因此适用于高温环境。三维烧结传感器与传统温度传感器的对比测试表明，两类传感器之间具有很高的相关性。由此得出的 R 平方值为 0.9885，令人满意，这意味着三维烧结传感器在温度传感应用中的可靠性和准确性令人满意。
{"title":"A High-Temperature Thermocouple Development by Additive Manufacturing: Tungsten-Nickel (W-Ni) and Molybdenum (Mo) Integration with Ceramic Structures","authors":"Azizul Islam, Vamsi Borra, Pedro Cortes","doi":"arxiv-2408.04800","DOIUrl":"https://doi.org/arxiv-2408.04800","url":null,"abstract":"Additive manufacturing holds more potential to enable the development of\u0000ceramic-based components. Ceramics offer high resistance to heat, high fracture\u0000toughness, and are extremely corrosion resistant. Thus, ceramics are widely\u0000used in sectors such as the aerospace industry, automotive, microelectronics,\u0000and biomedicine. Using various additive manufacturing platforms, ceramics with\u0000complex and uniquely designed geometry can be developed to suit specific\u0000applications. This project aims at innovating high-temperature thermocouples by\u0000embedding conductive metal pastes into a ceramic structure. The paste used\u0000includes tungsten, molybdenum, and antimony. The metal pastes are precisely\u0000extruded into a T-shaped trench inside the ceramic matrix. Following specific\u0000temperature ranges, the ceramic matrix is sintered to improve the properties of\u0000the material. The sensors produced can function at extremely high temperatures\u0000and are thereby suitable for high-temperature environments. Comparative testing\u0000of the 3D sintered sensors with conventional temperature sensors shows high\u0000correlation between the two classes of sensors. The resulting R-squared value\u0000of 0.9885 is satisfactory which implies the reliability and accuracy of 3D\u0000sintering sensors are satisfactory in temperature sensing applications.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"59 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141935822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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