Anoop Ajaya Kumar Nair, Julian Bessner, Timo Jacob, Elvar Örn Jónsson
We present an efficient momentum based perturbation scheme to evaluate polarizability tensors of small molecules and at the fraction of the computational cost compared to conventional energy based perturbation schemes. Furthermore, the simplicity of the scheme allows for the seamless integration into modern quantum chemistry codes. We apply the method to systems where the wavefunctions are described on a real-space grid and are therefore not subject to finite size basis set errors. In the grid-based scheme errors can be attributed to the resolution and the size of the grid-space. The applicability and generality of the method is exhibited by calculating polarizability tensors including the dipole-dipole and up to the quadrupole-quadrupole for a series of small molecules, representing the most common symmetry groups. By a direct comparison with standard techniques based on energy perturbation we show that the method reduces the number of explicit computations by a factor of 30. Numerical errors introduced due to the arrangement of the explicit point charges are eliminated with an extrapolation scheme to the effective zero-perturbation limit.
{"title":"Advanced perturbation scheme for efficient polarizability computations","authors":"Anoop Ajaya Kumar Nair, Julian Bessner, Timo Jacob, Elvar Örn Jónsson","doi":"arxiv-2409.10184","DOIUrl":"https://doi.org/arxiv-2409.10184","url":null,"abstract":"We present an efficient momentum based perturbation scheme to evaluate\u0000polarizability tensors of small molecules and at the fraction of the\u0000computational cost compared to conventional energy based perturbation schemes.\u0000Furthermore, the simplicity of the scheme allows for the seamless integration\u0000into modern quantum chemistry codes. We apply the method to systems where the\u0000wavefunctions are described on a real-space grid and are therefore not subject\u0000to finite size basis set errors. In the grid-based scheme errors can be\u0000attributed to the resolution and the size of the grid-space. The applicability\u0000and generality of the method is exhibited by calculating polarizability tensors\u0000including the dipole-dipole and up to the quadrupole-quadrupole for a series of\u0000small molecules, representing the most common symmetry groups. By a direct\u0000comparison with standard techniques based on energy perturbation we show that\u0000the method reduces the number of explicit computations by a factor of 30.\u0000Numerical errors introduced due to the arrangement of the explicit point\u0000charges are eliminated with an extrapolation scheme to the effective\u0000zero-perturbation limit.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142269163","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}
Roberto Hernández-Gómez, Dirk Tuma, Daniel Lozano-Martín, César R. Chamorro
The GERG-2008 equation of state is the approved ISO standard (ISO 20765-2) for the calculation of thermophysical properties of natural gas mixtures. The composition of natural gas can vary considerably due to the diversity of origin. Further diversification was generated by adding hydrogen, biogas, or other non-conventional energy gases. In this work, high-precision experimental ($p$, $rho$, $T$) data for two gravimetrically prepared synthetic natural gas mixtures are reported. One mixture resembled a conventional natural gas of 11 components (11 M) with a nominal mixture composition (amount-of-substance fraction) of 0.8845 for methane as the matrix compound. The other mixture was a 13-component hydrogen-enriched natural gas with a low calorific value featuring a nominal composition of 0.7885 for methane. Density measurements were performed in an isothermal operational mode at temperatures between 260 and 350 K and at pressures up to 20 MPa by using a single-sinker densimeter with magnetic suspension coupling. The data were compared with the corresponding densities calculated from both GERG-2008 and AGA8-DC92 equations of state to test their performance on real mixtures. The average absolute deviation from GERG-2008 (AGA8-DC92) is 0.027% (0.078%) for 11 M and 0.095% (0.062%) for the 13-component $H_{2}$-enriched mixture, respectively. The corresponding maximum relative deviation from GERG-2008 (AGA8-DC92) amounts to 0.095% (0.127%) for 11 M and 0.291% (0.193%) for the $H_{2}$-enriched mixture.
{"title":"Accurate experimental ($p$, $ρ$, $T$) data of natural gas mixtures for the assessment of reference equations of state when dealing with hydrogen-enriched natural gas","authors":"Roberto Hernández-Gómez, Dirk Tuma, Daniel Lozano-Martín, César R. Chamorro","doi":"arxiv-2409.09672","DOIUrl":"https://doi.org/arxiv-2409.09672","url":null,"abstract":"The GERG-2008 equation of state is the approved ISO standard (ISO 20765-2)\u0000for the calculation of thermophysical properties of natural gas mixtures. The\u0000composition of natural gas can vary considerably due to the diversity of\u0000origin. Further diversification was generated by adding hydrogen, biogas, or\u0000other non-conventional energy gases. In this work, high-precision experimental\u0000($p$, $rho$, $T$) data for two gravimetrically prepared synthetic natural gas\u0000mixtures are reported. One mixture resembled a conventional natural gas of 11\u0000components (11 M) with a nominal mixture composition (amount-of-substance\u0000fraction) of 0.8845 for methane as the matrix compound. The other mixture was a\u000013-component hydrogen-enriched natural gas with a low calorific value featuring\u0000a nominal composition of 0.7885 for methane. Density measurements were\u0000performed in an isothermal operational mode at temperatures between 260 and 350\u0000K and at pressures up to 20 MPa by using a single-sinker densimeter with\u0000magnetic suspension coupling. The data were compared with the corresponding\u0000densities calculated from both GERG-2008 and AGA8-DC92 equations of state to\u0000test their performance on real mixtures. The average absolute deviation from\u0000GERG-2008 (AGA8-DC92) is 0.027% (0.078%) for 11 M and 0.095% (0.062%) for the\u000013-component $H_{2}$-enriched mixture, respectively. The corresponding maximum\u0000relative deviation from GERG-2008 (AGA8-DC92) amounts to 0.095% (0.127%) for 11\u0000M and 0.291% (0.193%) for the $H_{2}$-enriched mixture.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258136","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}
A. Eschenlohr, R. Shi, J. Chen, P. Zhou, U. Bovensiepen, W. Hübner, G. Lefkidis
Metal-organic molecular adsorbates on metallic surfaces offer the potential to both generate materials for future (spin-)electronics applications as well as a better fundamental understanding of molecule-substrate interaction, provided that the electronic properties of such interfaces can be analyzed and/or manipulated in a targeted manner. To investigate electronic interactions at such interfaces, we measure optical second harmonic generation (SHG) from iron-octaethylporphyrin (FeOEP) adsorbed on Cu(001), and perform electronic structure calculations using coupled cluster methods including optical excitations. We find that the SHG response of FeOEP/Cu(001) is modified at 2.15-2.35 eV fundamental photon energy compared to the bare Cu(001) surface. Our polarization-dependent analysis shows that the $chi_{zzz}^{(2)}$ non-linear susceptibility tensor element dominates this modification. The first-principles calculations confirm this effect and conclude a resonantly enhanced SHG by molecular transitions at $hbaromega geq 2$ eV. We show that the enhancement of $chi^{(2)}_{zzz}$ results from a strong charge-transfer character of the molecule-substrate interaction. Our findings demonstrate the suitability of surface SHG for the characterization of such interfaces and the potential to employ it for time-resolved SHG experiments on optically induced electronic dynamics.
金属表面上的金属有机分子吸附剂既有可能为未来的（自旋）电子学应用生成材料，也有可能让人们从根本上更好地理解分子与基底的相互作用，前提是可以有针对性地分析和/或操纵这类界面的电子特性。为了研究这类界面上的电子相互作用，我们测量了吸附在铜（001）上的八乙基卟啉铁（FeOEP）产生的光学二次谐波（SHG），并利用包括光学激发在内的耦合簇方法进行了电子结构计算。我们发现，与裸铜(001)表面相比，FeOEP/Cu(001)的 SHG 响应在 2.15-2.35 eV 基本光子能量处发生了改变。我们的偏振依赖性分析表明，$chi_{zzz}^{(2)}$非线性感性张量元素主导了这种改变。第一原理计算证实了这一效应，并得出结论：在 $hbaromega geq 2$ eV 的分子跃迁会产生共振增强的 SHG。我们的研究结果表明，$chi^{(2)}_{zzz}$ 的增强源于分子与基底相互作用的强电荷转移特性。我们的研究结果表明，表面 SHG 适用于表征此类界面，并有潜力将其用于光诱导电子动力学的时间分辨 SHG 实验。
{"title":"Resonant molecular transitions in second harmonic generation spectroscopy of Fe-octaethylporphyrin adsorbed on Cu(001)","authors":"A. Eschenlohr, R. Shi, J. Chen, P. Zhou, U. Bovensiepen, W. Hübner, G. Lefkidis","doi":"arxiv-2409.09801","DOIUrl":"https://doi.org/arxiv-2409.09801","url":null,"abstract":"Metal-organic molecular adsorbates on metallic surfaces offer the potential\u0000to both generate materials for future (spin-)electronics applications as well\u0000as a better fundamental understanding of molecule-substrate interaction,\u0000provided that the electronic properties of such interfaces can be analyzed\u0000and/or manipulated in a targeted manner. To investigate electronic interactions\u0000at such interfaces, we measure optical second harmonic generation (SHG) from\u0000iron-octaethylporphyrin (FeOEP) adsorbed on Cu(001), and perform electronic\u0000structure calculations using coupled cluster methods including optical\u0000excitations. We find that the SHG response of FeOEP/Cu(001) is modified at\u00002.15-2.35 eV fundamental photon energy compared to the bare Cu(001) surface.\u0000Our polarization-dependent analysis shows that the $chi_{zzz}^{(2)}$\u0000non-linear susceptibility tensor element dominates this modification. The\u0000first-principles calculations confirm this effect and conclude a resonantly\u0000enhanced SHG by molecular transitions at $hbaromega geq 2$ eV. We show that\u0000the enhancement of $chi^{(2)}_{zzz}$ results from a strong charge-transfer\u0000character of the molecule-substrate interaction. Our findings demonstrate the\u0000suitability of surface SHG for the characterization of such interfaces and the\u0000potential to employ it for time-resolved SHG experiments on optically induced\u0000electronic dynamics.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258138","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}
Measurements of the speed of sound in gaseous cis-1,3,3,3-tetrafluoroprop-1-ene, (R1234ze(Z)), are presented. The measurements were performed using a quasi-spherical acoustic resonator at temperatures between 307 K and 420 K and pressures up to 1.8 MPa. Ideal-gas heat capacities and acoustic virial coefficients over the same temperature range were directly calculated from the results. The relative accuracy of our determinations of the speed of sound $w$($p$,$T$) of R1234ze(Z) was approximately $pm$ 0.02%. The accuracy of the determination of the ideal gas heat capacity ratio ${gamma}^{0}$($T$) was approximately $pm$ 0.25%. These data were found to be mostly consistent with the predictions of a fundamental equation of state of R1234ze(Z).
本文介绍了气体-1,3,3,3-四氟丙烯（R1234ze(Z)）中的声速测量结果。测量使用准球形声共振器进行，温度介于 307 K 和 420 K 之间，压力高达 1.8 MPa。根据测量结果直接计算了同一温度范围内的理想气体热容量和声学病毒系数。我们测定的 R1234ze(Z) 的声速 $w$($p$,$T$)的相对精度约为 $pm$ 0.02%。理想气体热容比 ${{gamma}^{0}$($T$)的测定精度约为 $/pm$ 0.25%。研究发现，这些数据与 R1234ze(Z)的基本状态方程的预测基本一致。
{"title":"Speed of sound in gaseous cis-1,3,3,3-tetrafluoropropene (R1234ze(Z)) between 307 K and 420 K","authors":"D. Lozano-Martín, D. Madonna Ripa, R. M. Gavioso","doi":"arxiv-2409.08722","DOIUrl":"https://doi.org/arxiv-2409.08722","url":null,"abstract":"Measurements of the speed of sound in gaseous\u0000cis-1,3,3,3-tetrafluoroprop-1-ene, (R1234ze(Z)), are presented. The\u0000measurements were performed using a quasi-spherical acoustic resonator at\u0000temperatures between 307 K and 420 K and pressures up to 1.8 MPa. Ideal-gas\u0000heat capacities and acoustic virial coefficients over the same temperature\u0000range were directly calculated from the results. The relative accuracy of our\u0000determinations of the speed of sound $w$($p$,$T$) of R1234ze(Z) was\u0000approximately $pm$ 0.02%. The accuracy of the determination of the ideal gas\u0000heat capacity ratio ${gamma}^{0}$($T$) was approximately $pm$ 0.25%. These\u0000data were found to be mostly consistent with the predictions of a fundamental\u0000equation of state of R1234ze(Z).","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258195","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}
The Finke-Watkzy model is the reaction set consisting of autocatalysis, A + B --> 2B and the first order process A --> B. It has been widely used to describe phenomena as diverse as the formation of transition metal nanoparticles and protein misfolding and aggregation. It can also be regarded as a simple model for the spread of a non-fatal but incurable disease. The deterministic rate equations for this reaction set are easy to solve and the solution is used in the literature to fit experimental data. However, some applications of the Finke-Watkzy model may involve systems with a small number of molecules or individuals. In such cases, a stochastic description using a Chemical Master Equation or Gillespie's Stochastic Simulation Algorithm is more appropriate than a deterministic one. This is even more so because for this particular set of chemical reactions, the differences between deterministic and stochastic kinetics can be very significant. Here, we derive an analytical solution of the Chemical Master Equation for the Finke-Watkzy model. We consider both the original formulation of the model, where the reactions are assumed to be irreversible, and its generalization to the case of reversible reactions. For the former, we obtain analytical expressions for the time dependence of the probabilities of the number of A molecules. For the latter, we derive the corresponding steady-state probability distribution. Our findings may have implications for modeling the spread of epidemics and chemical reactions in living cells.
芬克-瓦茨模型是由自催化反应、A + B--> 2B 和一阶过程 A --> B 组成的反应集合。它被广泛用于描述过渡金属纳米粒子的形成、蛋白质的错误折叠和聚集等各种现象。它也可以被视为一种非致命但无法治愈的疾病传播的简单模式。该反应集的确定性速率方程很容易求解，文献中也用其来拟合实验数据。然而，芬克-瓦特奇模型的某些应用可能涉及分子或个体数量较少的系统。在这种情况下，使用化学主方程或 Gillespie 随机模拟算法进行随机描述比确定性描述更为合适。对于这组特殊的化学反应，确定性动力学和随机动力学之间的差异可能会非常大，这一点更为重要。在这里，我们推导出 Finke-Watkzy 模型的化学主方程的解析解。我们既考虑了假设反应是可逆的该模型的原始公式，也考虑了其对可逆反应情况的概括。对于前者，我们得到了 A 分子数概率随时间变化的分析表达式。对于后者，我们推导出了相应的稳态概率分布。我们的发现可能会对流行病的传播和活细胞中的化学反应建模产生影响。
{"title":"Exact analytical solution of the Chemical Master Equation for the Finke-Watkzy model","authors":"Tomasz Bednarek, Jakub Jędrak","doi":"arxiv-2409.08875","DOIUrl":"https://doi.org/arxiv-2409.08875","url":null,"abstract":"The Finke-Watkzy model is the reaction set consisting of autocatalysis, A + B\u0000--> 2B and the first order process A --> B. It has been widely used to describe\u0000phenomena as diverse as the formation of transition metal nanoparticles and\u0000protein misfolding and aggregation. It can also be regarded as a simple model\u0000for the spread of a non-fatal but incurable disease. The deterministic rate\u0000equations for this reaction set are easy to solve and the solution is used in\u0000the literature to fit experimental data. However, some applications of the\u0000Finke-Watkzy model may involve systems with a small number of molecules or\u0000individuals. In such cases, a stochastic description using a Chemical Master\u0000Equation or Gillespie's Stochastic Simulation Algorithm is more appropriate\u0000than a deterministic one. This is even more so because for this particular set\u0000of chemical reactions, the differences between deterministic and stochastic\u0000kinetics can be very significant. Here, we derive an analytical solution of the\u0000Chemical Master Equation for the Finke-Watkzy model. We consider both the\u0000original formulation of the model, where the reactions are assumed to be\u0000irreversible, and its generalization to the case of reversible reactions. For\u0000the former, we obtain analytical expressions for the time dependence of the\u0000probabilities of the number of A molecules. For the latter, we derive the\u0000corresponding steady-state probability distribution. Our findings may have\u0000implications for modeling the spread of epidemics and chemical reactions in\u0000living cells.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258193","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}
Subsurface oxygen in oxide-derived copper catalysts significantly influences CO$_2$ activation. However, its effect on the molecular charging process, the key to forming the CO$_2^{delta-}$ intermediate, remains poorly understood. We employ many-body perturbation theory to investigate the impact of the structural factors induced by the subsurface oxygen on charged activation of CO$_2$. By computing the molecular single-particle state energy of the electron-accepting orbital ($sigma*$) on Cu (111) surface, we examined how this molecular quasi-particle (QP) energy changes with varied vicinity of adsorption and multiple subsurface oxygen configuration. We demonstrate that subsurface oxygen impairs CO$_2$ charging, with its presence and density being influential factors. The non-local potential proves substantial for accurate excitation energy predictions yet is not sensitive to minor atomic structural changes. More importantly, state delocalization and hybridization are critical for determining QP energy. These insights are enlightening for designing atomic architectures to optimize catalytic performance on modified surfaces.
{"title":"Impact of Subsurface Oxygen on CO2 Charging Energy Changes in Cu Surfaces","authors":"Xiaohe Lei, Vojtech Vlcek","doi":"arxiv-2409.08433","DOIUrl":"https://doi.org/arxiv-2409.08433","url":null,"abstract":"Subsurface oxygen in oxide-derived copper catalysts significantly influences\u0000CO$_2$ activation. However, its effect on the molecular charging process, the\u0000key to forming the CO$_2^{delta-}$ intermediate, remains poorly understood. We\u0000employ many-body perturbation theory to investigate the impact of the\u0000structural factors induced by the subsurface oxygen on charged activation of\u0000CO$_2$. By computing the molecular single-particle state energy of the\u0000electron-accepting orbital ($sigma*$) on Cu (111) surface, we examined how\u0000this molecular quasi-particle (QP) energy changes with varied vicinity of\u0000adsorption and multiple subsurface oxygen configuration. We demonstrate that\u0000subsurface oxygen impairs CO$_2$ charging, with its presence and density being\u0000influential factors. The non-local potential proves substantial for accurate\u0000excitation energy predictions yet is not sensitive to minor atomic structural\u0000changes. More importantly, state delocalization and hybridization are critical\u0000for determining QP energy. These insights are enlightening for designing atomic\u0000architectures to optimize catalytic performance on modified surfaces.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258196","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}
Enes Suyabatmaz, Gustavo J. R. Aroeira, Raphael F. Ribeiro
Vibrational strong light-matter coupling offers a promising approach for controlling chemical reactivity with infrared microcavities. This study explores the dynamics of Blackbody Infrared Radiative Dissociation (BIRD) in microcavities under weak and strong light-matter interaction regimes. Using a Master equation approach, we simulate the effects of infrared field confinement and vibrational strong coupling on BIRD rates for diatomic molecules. We present a framework explaining how infrared microcavities influence BIRD kinetics, highlighting the importance of overtone transitions in the process. Our findings reveal conditions for significant enhancement and mild suppression of radiative dissociation, establishing upper bounds for BIRD rates under weak and strong coupling. These results provide new strategies and limitations for controlling reactive processes with infrared resonators.
{"title":"Polaritonic control of blackbody infrared radiative dissociation","authors":"Enes Suyabatmaz, Gustavo J. R. Aroeira, Raphael F. Ribeiro","doi":"arxiv-2409.09000","DOIUrl":"https://doi.org/arxiv-2409.09000","url":null,"abstract":"Vibrational strong light-matter coupling offers a promising approach for\u0000controlling chemical reactivity with infrared microcavities. This study\u0000explores the dynamics of Blackbody Infrared Radiative Dissociation (BIRD) in\u0000microcavities under weak and strong light-matter interaction regimes. Using a\u0000Master equation approach, we simulate the effects of infrared field confinement\u0000and vibrational strong coupling on BIRD rates for diatomic molecules. We\u0000present a framework explaining how infrared microcavities influence BIRD\u0000kinetics, highlighting the importance of overtone transitions in the process.\u0000Our findings reveal conditions for significant enhancement and mild suppression\u0000of radiative dissociation, establishing upper bounds for BIRD rates under weak\u0000and strong coupling. These results provide new strategies and limitations for\u0000controlling reactive processes with infrared resonators.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258192","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}
The change of the vibrational energy within a molecule after collisions with another molecule plays an essential role in the evolution of molecular internal energy distributions, which is also the limiting process in the relaxation of the gas towards equilibrium. Here we investigate the energy transfer between the translational motion and the vibrational motion of the diatom during the atom-diatom collision, the simplest case involving the transfer between inter-molecular and intra-molecular energies. We are interested in the situation when the translational temperature of the gas is high, in which case there are significant probabilities for the vibrational energy to change over widely separated energy levels after a collision. Data from quasi-classical trajectory simulations of the N+N$_2$ system with textit{ab initio} potential energies suggest that the transition probability dependence on the collisional energy possesses an ``activation-saturation'' behavior and can be described by a simple model. The model allows for explicit evaluation of the vibrational state-to-state transition rate coefficients, from which the evolution of the vibrational energy distribution from any initial conditions can be solved by the master equation approach. An example of the vibrational energy relaxation in the N+N$_2$ system mimicking the gas behind strong shocks in a hypersonic flow is shown and the results are in good agreement with available data.
{"title":"High-Temperature Non-Equilibrium Atom-Diatom Collisional Energy Transfer","authors":"Xiaorui Zhao, Xuefei Xu, Haitao Xu","doi":"arxiv-2409.08955","DOIUrl":"https://doi.org/arxiv-2409.08955","url":null,"abstract":"The change of the vibrational energy within a molecule after collisions with\u0000another molecule plays an essential role in the evolution of molecular internal\u0000energy distributions, which is also the limiting process in the relaxation of\u0000the gas towards equilibrium. Here we investigate the energy transfer between\u0000the translational motion and the vibrational motion of the diatom during the\u0000atom-diatom collision, the simplest case involving the transfer between\u0000inter-molecular and intra-molecular energies. We are interested in the\u0000situation when the translational temperature of the gas is high, in which case\u0000there are significant probabilities for the vibrational energy to change over\u0000widely separated energy levels after a collision. Data from quasi-classical\u0000trajectory simulations of the N+N$_2$ system with textit{ab initio} potential\u0000energies suggest that the transition probability dependence on the collisional\u0000energy possesses an ``activation-saturation'' behavior and can be described by\u0000a simple model. The model allows for explicit evaluation of the vibrational\u0000state-to-state transition rate coefficients, from which the evolution of the\u0000vibrational energy distribution from any initial conditions can be solved by\u0000the master equation approach. An example of the vibrational energy relaxation\u0000in the N+N$_2$ system mimicking the gas behind strong shocks in a hypersonic\u0000flow is shown and the results are in good agreement with available data.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258198","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}
Due to the absorption of high energetic ultraviolet (UV) photons by the surface layers of the cold molecular clouds, only low energetic photons are able to penetrate into the inner regions of these clouds. This leads to lower photo-ionization yield of molecules of higher ionization potential in these environments. However, here we have experimentally shown the ionization of Benzonitrile molecule using 266nm (4.66eV) photons. The low intensity and unfocused laser irradiation of benzonitrile molecules results extensive fragmentation. Moreover, the ion-neutral reactions among the cationic fragments and neutral fragments shows promising molecular mass growth.
{"title":"Photo-induced molecular growth of benzonitrile in the gas phase","authors":"Nihar Ranjan Behera, Arun Kumar Kanakati, Pratikkumar Thakkar, Siddhartha Sankar Payra, Saurav Dutta, Saroj Barik, Yash Lenka, G Aravind","doi":"arxiv-2409.08590","DOIUrl":"https://doi.org/arxiv-2409.08590","url":null,"abstract":"Due to the absorption of high energetic ultraviolet (UV) photons by the\u0000surface layers of the cold molecular clouds, only low energetic photons are\u0000able to penetrate into the inner regions of these clouds. This leads to lower\u0000photo-ionization yield of molecules of higher ionization potential in these\u0000environments. However, here we have experimentally shown the ionization of\u0000Benzonitrile molecule using 266nm (4.66eV) photons. The low intensity and\u0000unfocused laser irradiation of benzonitrile molecules results extensive\u0000fragmentation. Moreover, the ion-neutral reactions among the cationic fragments\u0000and neutral fragments shows promising molecular mass growth.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142258194","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}
Rina Ibragimova, Mikhail S. Kuklin, Tigany Zarrouk, Miguel A. Caro
We present a general-purpose machine learning (ML) interatomic potential for carbon and hydrogen which is capable of simulating various materials and molecules composed of these elements. This ML interatomic potential is trained using the Gaussian approximation potential (GAP) framework and an extensive dataset of C-H configurations obtained from density functional theory. The dataset is constructed through iterative training and structure-search techniques that generate a broad range of configurations to comprehensively sample the potential energy surface. Furthermore, the dataset is supplemented with relevant bulk, molecular, and high-pressure structures. Finally, long-range van der Waals interactions are added as a locally parametrized model. The accuracy and generality of the potential are validated through the analysis of different simulations under a wide range of conditions, including weak interactions, high temperature, and high pressure. We show that our CH GAP model describes different problems such as the formation of simple and complex alkanes, aromatic hydrocarbons, hydrogenated amorphous carbon (a-C:H), and CH systems at extreme conditions, while retaining good accuracy for pure carbon materials. We use this model to generate hydrocarbons of different sizes and complexity without prior knowledge of organic chemistry rules, and to highlight intrinsic limitations to the simultaneous description on intra and intermolecular interactions within a single computational framework. Our general-purpose ML interatomic potential has the capability to significantly advance research in the field of H-containing carbon materials and compounds, particularly in the areas where longer dynamics, reactivity and large-scale effects may be important.
我们提出了一种通用的机器学习（ML）碳氢原子间势，它能够模拟由这些元素组成的各种材料和分子。这种 ML 原子间位势是利用高斯近似位势（GAP）框架和从密度泛函理论获得的 C-H 构型扩展数据集进行训练的。该数据集是通过迭代训练和结构搜索技术构建的，可生成广泛的构型，从而对势能面进行全面采样。此外，数据集还补充了相关的块体、分子和高压结构。最后，长程范德瓦耳斯相互作用被添加为局部参数化模型。通过分析各种条件下的模拟（包括弱相互作用、高温和高压），我们验证了该势垒的准确性和通用性。我们的研究表明，我们的 CH GAP 模型可以描述不同的问题，例如在极端条件下简单和复杂烷烃、芳香烃、氢化无定形碳（a-C:H）和 CH 系统的形成，同时对纯碳材料保持良好的准确性。我们利用该模型生成了不同大小和复杂程度的碳氢化合物，而无需事先了解有机化学规则，并强调了在单一计算框架内同时描述分子内和分子间相互作用的内在局限性。我们的通用 ML 原子间势能极大地推动了含氢碳材料和化合物领域的研究，尤其是在长动力学、反应性和大尺度效应可能很重要的领域。
{"title":"Unifying the description of hydrocarbons and hydrogenated carbon materials with a chemically reactive machine learning interatomic potential","authors":"Rina Ibragimova, Mikhail S. Kuklin, Tigany Zarrouk, Miguel A. Caro","doi":"arxiv-2409.08194","DOIUrl":"https://doi.org/arxiv-2409.08194","url":null,"abstract":"We present a general-purpose machine learning (ML) interatomic potential for\u0000carbon and hydrogen which is capable of simulating various materials and\u0000molecules composed of these elements. This ML interatomic potential is trained\u0000using the Gaussian approximation potential (GAP) framework and an extensive\u0000dataset of C-H configurations obtained from density functional theory. The\u0000dataset is constructed through iterative training and structure-search\u0000techniques that generate a broad range of configurations to comprehensively\u0000sample the potential energy surface. Furthermore, the dataset is supplemented\u0000with relevant bulk, molecular, and high-pressure structures. Finally,\u0000long-range van der Waals interactions are added as a locally parametrized\u0000model. The accuracy and generality of the potential are validated through the\u0000analysis of different simulations under a wide range of conditions, including\u0000weak interactions, high temperature, and high pressure. We show that our CH GAP\u0000model describes different problems such as the formation of simple and complex\u0000alkanes, aromatic hydrocarbons, hydrogenated amorphous carbon (a-C:H), and CH\u0000systems at extreme conditions, while retaining good accuracy for pure carbon\u0000materials. We use this model to generate hydrocarbons of different sizes and\u0000complexity without prior knowledge of organic chemistry rules, and to highlight\u0000intrinsic limitations to the simultaneous description on intra and\u0000intermolecular interactions within a single computational framework. Our\u0000general-purpose ML interatomic potential has the capability to significantly\u0000advance research in the field of H-containing carbon materials and compounds,\u0000particularly in the areas where longer dynamics, reactivity and large-scale\u0000effects may be important.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190242","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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