Hartmut Maennel, Oliver T. Unke, Klaus-Robert Müller
When modeling physical properties of molecules with machine learning, it is desirable to incorporate $SO(3)$-covariance. While such models based on low body order features are not complete, we formulate and prove general completeness properties for higher order methods, and show that $6k-5$ of these features are enough for up to $k$ atoms. We also find that the Clebsch--Gordan operations commonly used in these methods can be replaced by matrix multiplications without sacrificing completeness, lowering the scaling from $O(l^6)$ to $O(l^3)$ in the degree of the features. We apply this to quantum chemistry, but the proposed methods are generally applicable for problems involving 3D point configurations.
{"title":"Complete and Efficient Covariants for 3D Point Configurations with Application to Learning Molecular Quantum Properties","authors":"Hartmut Maennel, Oliver T. Unke, Klaus-Robert Müller","doi":"arxiv-2409.02730","DOIUrl":"https://doi.org/arxiv-2409.02730","url":null,"abstract":"When modeling physical properties of molecules with machine learning, it is\u0000desirable to incorporate $SO(3)$-covariance. While such models based on low\u0000body order features are not complete, we formulate and prove general\u0000completeness properties for higher order methods, and show that $6k-5$ of these\u0000features are enough for up to $k$ atoms. We also find that the Clebsch--Gordan\u0000operations commonly used in these methods can be replaced by matrix\u0000multiplications without sacrificing completeness, lowering the scaling from\u0000$O(l^6)$ to $O(l^3)$ in the degree of the features. We apply this to quantum\u0000chemistry, but the proposed methods are generally applicable for problems\u0000involving 3D point configurations.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190332","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}
Instanton theory relates the rate constant for tunneling through a barrier to the periodic classical trajectory on the upturned potential energy surface whose period is $tau=hbar /(k_{mathrm{B}}T)$. Unfortunately, the standard theory is only applicable below the "crossover temperature", where the periodic orbit first appears. This paper presents a rigorous semiclassical ($hbarto0$) theory for the rate that is valid at any temperature. The theory is derived by combining Bleistein's method for generating uniform asymptotic expansions with a real-time modification of Richardson's flux-correlation function derivation of instanton theory. The resulting theory smoothly connects the instanton result at low temperature to the parabolic correction to Eyring transition state theory at high-temperature. Although the derivation involves real time, the final theory only involves imaginary-time (thermal) properties, consistent with the standard theory. Therefore, it is no more difficult to compute than the standard theory. The theory is illustrated with application to model systems, where it is shown to give excellent numerical results. Finally, the first-principles approach taken here results in a number of advantages over previous attempts to extend the imaginary free-energy formulation of instanton theory. In addition to producing a theory that is a smooth (continuously differentiable) function of temperature, the derivation also naturally incorporates hyperasymptotic (i.e.~multi-orbit) terms, and provides a framework for further extensions of the theory.
{"title":"Semiclassical instanton theory for reaction rates at any temperature: How a rigorous real-time derivation solves the crossover temperature problem","authors":"Joseph E. Lawrence","doi":"arxiv-2409.02820","DOIUrl":"https://doi.org/arxiv-2409.02820","url":null,"abstract":"Instanton theory relates the rate constant for tunneling through a barrier to\u0000the periodic classical trajectory on the upturned potential energy surface\u0000whose period is $tau=hbar /(k_{mathrm{B}}T)$. Unfortunately, the standard\u0000theory is only applicable below the \"crossover temperature\", where the periodic\u0000orbit first appears. This paper presents a rigorous semiclassical ($hbarto0$)\u0000theory for the rate that is valid at any temperature. The theory is derived by\u0000combining Bleistein's method for generating uniform asymptotic expansions with\u0000a real-time modification of Richardson's flux-correlation function derivation\u0000of instanton theory. The resulting theory smoothly connects the instanton\u0000result at low temperature to the parabolic correction to Eyring transition\u0000state theory at high-temperature. Although the derivation involves real time,\u0000the final theory only involves imaginary-time (thermal) properties, consistent\u0000with the standard theory. Therefore, it is no more difficult to compute than\u0000the standard theory. The theory is illustrated with application to model\u0000systems, where it is shown to give excellent numerical results. Finally, the\u0000first-principles approach taken here results in a number of advantages over\u0000previous attempts to extend the imaginary free-energy formulation of instanton\u0000theory. In addition to producing a theory that is a smooth (continuously\u0000differentiable) function of temperature, the derivation also naturally\u0000incorporates hyperasymptotic (i.e.~multi-orbit) terms, and provides a framework\u0000for further extensions of the theory.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190328","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}
As an approximation to SDSCI [static-dynamic-static (SDS) configuration interaction (CI), a minimal MRCI; Theor. Chem. Acc. 133, 1481 (2014)], SDSPT2 [Mol. Phys. 115, 2696 (2017)] is a CI-like multireference (MR) second-order perturbation theory (PT2) that treats single and multiple roots on an equal footing. This feature permits the use of configuration selection over a large complete active space (CAS) $P$ to end up with a much reduced reference space $tilde{P}$, which is connected only with a portion ($tilde{Q}_1$) of the full first-order interacting space $Q$ connected to $P$. The effective interacting $tilde{Q}$ space can further be truncated by an integral-based cutoff threshold. With marginal loss of accuracy, the selection-truncation procedure, along with an efficient evaluation and storage of internal contraction coefficients, renders SDSPT2s (SDSPT2 with selection) applicable to systems that cannot be handled by the parent CAS-based SDSPT2, as demonstrated by several challenging showcases.
{"title":"SDSPT2s: SDSPT2 with Selection","authors":"Yibo Lei, Yang Guo, Bingbing Suo, Wenjian Liu","doi":"arxiv-2409.02367","DOIUrl":"https://doi.org/arxiv-2409.02367","url":null,"abstract":"As an approximation to SDSCI [static-dynamic-static (SDS) configuration\u0000interaction (CI), a minimal MRCI; Theor. Chem. Acc. 133, 1481 (2014)], SDSPT2\u0000[Mol. Phys. 115, 2696 (2017)] is a CI-like multireference (MR) second-order\u0000perturbation theory (PT2) that treats single and multiple roots on an equal\u0000footing. This feature permits the use of configuration selection over a large\u0000complete active space (CAS) $P$ to end up with a much reduced reference space\u0000$tilde{P}$, which is connected only with a portion ($tilde{Q}_1$) of the full\u0000first-order interacting space $Q$ connected to $P$. The effective interacting\u0000$tilde{Q}$ space can further be truncated by an integral-based cutoff\u0000threshold. With marginal loss of accuracy, the selection-truncation procedure,\u0000along with an efficient evaluation and storage of internal contraction\u0000coefficients, renders SDSPT2s (SDSPT2 with selection) applicable to systems\u0000that cannot be handled by the parent CAS-based SDSPT2, as demonstrated by\u0000several challenging showcases.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"161 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190331","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}
Full-dimensional (12D) vibrational states of the methanol molecule (CH$_3$OH) have been computed using the GENIUSH-Smolyak approach and the potential energy surface from Qu and Bowman (2013). All vibrational energies are converged better than 0.5 cm$^{-1}$ with respect to the basis and grid size up to the first overtone of the CO stretch, ca. 2000 cm$^{-1}$ beyond the zero-point vibrational energy. About seventy torsion-vibration states are reported and assigned. The computed vibrational energies agree with the available experimental data within less than a few cm$^{-1}$ in most cases, which confirms the good accuracy of the potential energy surface. The computations are carried out using curvilinear normal coordinates with the option of path-following coefficients which minimize the coupling of the small- and large-amplitude motions. It is important to ensure tight numerical fulfilment of the $C_{3mathrm{v}}$(M) molecular symmetry for every geometry and coefficient set used to define the curvilinear normal coordinates along the torsional coordinate to obtain a faithful description of degeneracy in this floppy system. The reported values may provide a computational reference for fundamental spectroscopy, astrochemistry, and for the search of the proton-to-electron mass ratio variation using the methanol molecule.
{"title":"Variational Vibrational States of Methanol (12D)","authors":"Ayaki Sunaga, Gustavo Avila, Edit Matyus","doi":"arxiv-2409.02505","DOIUrl":"https://doi.org/arxiv-2409.02505","url":null,"abstract":"Full-dimensional (12D) vibrational states of the methanol molecule (CH$_3$OH)\u0000have been computed using the GENIUSH-Smolyak approach and the potential energy\u0000surface from Qu and Bowman (2013). All vibrational energies are converged\u0000better than 0.5 cm$^{-1}$ with respect to the basis and grid size up to the\u0000first overtone of the CO stretch, ca. 2000 cm$^{-1}$ beyond the zero-point\u0000vibrational energy. About seventy torsion-vibration states are reported and\u0000assigned. The computed vibrational energies agree with the available\u0000experimental data within less than a few cm$^{-1}$ in most cases, which\u0000confirms the good accuracy of the potential energy surface. The computations\u0000are carried out using curvilinear normal coordinates with the option of\u0000path-following coefficients which minimize the coupling of the small- and\u0000large-amplitude motions. It is important to ensure tight numerical fulfilment\u0000of the $C_{3mathrm{v}}$(M) molecular symmetry for every geometry and\u0000coefficient set used to define the curvilinear normal coordinates along the\u0000torsional coordinate to obtain a faithful description of degeneracy in this\u0000floppy system. The reported values may provide a computational reference for\u0000fundamental spectroscopy, astrochemistry, and for the search of the\u0000proton-to-electron mass ratio variation using the methanol molecule.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190329","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}
Joseph M. Cavanagh, Kunyang Sun, Andrew Gritsevskiy, Dorian Bagni, Thomas D. Bannister, Teresa Head-Gordon
Here we show that a Large Language Model (LLM) can serve as a foundation model for a Chemical Language Model (CLM) which performs at or above the level of CLMs trained solely on chemical SMILES string data. Using supervised fine-tuning (SFT) and direct preference optimization (DPO) on the open-source Llama LLM, we demonstrate that we can train an LLM to respond to prompts such as generating molecules with properties of interest to drug development. This overall framework allows an LLM to not just be a chatbot client for chemistry and materials tasks, but can be adapted to speak more directly as a CLM which can generate molecules with user-specified properties.
{"title":"SmileyLlama: Modifying Large Language Models for Directed Chemical Space Exploration","authors":"Joseph M. Cavanagh, Kunyang Sun, Andrew Gritsevskiy, Dorian Bagni, Thomas D. Bannister, Teresa Head-Gordon","doi":"arxiv-2409.02231","DOIUrl":"https://doi.org/arxiv-2409.02231","url":null,"abstract":"Here we show that a Large Language Model (LLM) can serve as a foundation\u0000model for a Chemical Language Model (CLM) which performs at or above the level\u0000of CLMs trained solely on chemical SMILES string data. Using supervised\u0000fine-tuning (SFT) and direct preference optimization (DPO) on the open-source\u0000Llama LLM, we demonstrate that we can train an LLM to respond to prompts such\u0000as generating molecules with properties of interest to drug development. This\u0000overall framework allows an LLM to not just be a chatbot client for chemistry\u0000and materials tasks, but can be adapted to speak more directly as a CLM which\u0000can generate molecules with user-specified properties.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"60 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142224812","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}
Mikhail V. Vaganov, Nicolas Suaud, Francois Lambert, Benjamin Cahier, Christian Herrero, Regis Guillot, Anne-Laure Barra, Nathalie Guihery, Talal Mallah, Arzhang Ardavan, Junjie Liu
Controlling quantum spins using electric rather than magnetic fields promises significant architectural advantages for developing quantum technologies. In this context, spins in molecular nanomagnets offer tunability of spin-electric couplings (SEC) by rational chemical design. Here we demonstrate systematic control of SECs in a family of Mn(II)-containing molecules via chemical engineering. The trigonal bipyramidal (tbp) molecular structure with C3 symmetry leads to a significant molecular electric dipole moment that is directly connected to its magnetic anisotropy. The interplay between these two features gives rise to significant experimentally observed SECs, which can be rationalised by wavefunction theoretical calculations. Our findings guide strategies for the development of electrically controllable molecular spin qubits for quantum technologies.
{"title":"Chemical tuning of quantum spin-electric coupling in molecular nanomagnets","authors":"Mikhail V. Vaganov, Nicolas Suaud, Francois Lambert, Benjamin Cahier, Christian Herrero, Regis Guillot, Anne-Laure Barra, Nathalie Guihery, Talal Mallah, Arzhang Ardavan, Junjie Liu","doi":"arxiv-2409.01982","DOIUrl":"https://doi.org/arxiv-2409.01982","url":null,"abstract":"Controlling quantum spins using electric rather than magnetic fields promises\u0000significant architectural advantages for developing quantum technologies. In\u0000this context, spins in molecular nanomagnets offer tunability of spin-electric\u0000couplings (SEC) by rational chemical design. Here we demonstrate systematic\u0000control of SECs in a family of Mn(II)-containing molecules via chemical\u0000engineering. The trigonal bipyramidal (tbp) molecular structure with C3\u0000symmetry leads to a significant molecular electric dipole moment that is\u0000directly connected to its magnetic anisotropy. The interplay between these two\u0000features gives rise to significant experimentally observed SECs, which can be\u0000rationalised by wavefunction theoretical calculations. Our findings guide\u0000strategies for the development of electrically controllable molecular spin\u0000qubits for quantum technologies.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"73 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190212","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}
Daniel Lozano-Martín, Fatemeh Pazoki, Heinrich Kipphardt, Peyman Khanipour, Dirk Tuma, Alfonso Horrillo, César R. Chamorro
The injection of hydrogen into the natural-gas grid is an alternative during the process of a gradual decarbonization of the heat and power supply. When dealing with hydrogen-enriched natural gas mixtures, the performance of the reference equations of state habitually used for natural gas should be validated by using high-precision experimental thermophysical data from multicomponent reference mixtures prepared with the lowest possible uncertainty in composition. In this work, we present experimental density data for an 11-compound high-calorific (hydrogen-free) natural gas mixture and for two derived hydrogen-enriched natural gas mixtures prepared by adding (10 and 20) mol-% of hydrogen to the original standard natural gas mixture. The three mixtures were prepared gravimetrically according to ISO 6142-1 for maximum precision in their composition and thus qualify for reference materials. A single-sinker densimeter was used to determine the density of the mixtures from (250-350) K and up to 20 MPa. The experimental density results of this work have been compared to the densities calculated by three different reference equations of state for natural gas related mixtures: the AGA8-DC92 EoS, the GERG-2008 EoS, and an improved version of the GERG-2008 EoS. While relative deviations of the experimental density data for the hydrogen-free natural gas mixture are always within the claimed uncertainty of the three considered equations of state, larger deviations can be observed for the hydrogen-enriched natural gas mixtures from any of the three equations of state, especially for the lowest temperature and the highest pressures.
在热能和电力供应逐步去碳化的过程中，向天然气电网注入氢气是一种替代方法。在处理富氢天然气混合物时，应使用多组分参考混合物的高精度实验热物理数据来验证惯常用于天然气的状态参考方程的性能，并尽可能降低成分的不确定性。在这项工作中，我们展示了 11 种高热量（无氢）天然气混合物的实验密度数据，以及在原始标准天然气混合物中加入（10 和 20）摩尔-% 的氢而制备的两种富氢天然气混合物的实验密度数据。这三种混合物都是根据 ISO 6142-1 以重力法制备的，以保证其成分的最大精确性，因此符合标准物质的要求。使用单沉式密度计测定了混合物在（250-350）K 和高达 20 MPa 下的密度。这项工作的实验密度结果与天然气相关混合物的三种不同参考状态方程计算的密度进行了比较：AGA8-DC92 EoS、GERG-2008 EoS 和 GERG-2008 EoS 的改进版。虽然无氢天然气混合物的实验密度数据的相关偏差始终在三个参考状态方程的声称不确定性范围内，但可以观察到富氢天然气混合物与三个状态方程中任何一个的偏差都较大，尤其是在最低温度和最高压力下。
{"title":"Thermodynamic ($p,ρ,T$) characterization of a reference high-calorific natural gas mixture when hydrogen is added up to 20 % (mol/mol)","authors":"Daniel Lozano-Martín, Fatemeh Pazoki, Heinrich Kipphardt, Peyman Khanipour, Dirk Tuma, Alfonso Horrillo, César R. Chamorro","doi":"arxiv-2409.01702","DOIUrl":"https://doi.org/arxiv-2409.01702","url":null,"abstract":"The injection of hydrogen into the natural-gas grid is an alternative during\u0000the process of a gradual decarbonization of the heat and power supply. When\u0000dealing with hydrogen-enriched natural gas mixtures, the performance of the\u0000reference equations of state habitually used for natural gas should be\u0000validated by using high-precision experimental thermophysical data from\u0000multicomponent reference mixtures prepared with the lowest possible uncertainty\u0000in composition. In this work, we present experimental density data for an\u000011-compound high-calorific (hydrogen-free) natural gas mixture and for two\u0000derived hydrogen-enriched natural gas mixtures prepared by adding (10 and 20)\u0000mol-% of hydrogen to the original standard natural gas mixture. The three\u0000mixtures were prepared gravimetrically according to ISO 6142-1 for maximum\u0000precision in their composition and thus qualify for reference materials. A\u0000single-sinker densimeter was used to determine the density of the mixtures from\u0000(250-350) K and up to 20 MPa. The experimental density results of this work\u0000have been compared to the densities calculated by three different reference\u0000equations of state for natural gas related mixtures: the AGA8-DC92 EoS, the\u0000GERG-2008 EoS, and an improved version of the GERG-2008 EoS. While relative\u0000deviations of the experimental density data for the hydrogen-free natural gas\u0000mixture are always within the claimed uncertainty of the three considered\u0000equations of state, larger deviations can be observed for the hydrogen-enriched\u0000natural gas mixtures from any of the three equations of state, especially for\u0000the lowest temperature and the highest pressures.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190333","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 recently synthesized M"obius carbon nanobelts (CNBs) have gained attention owing to their unique $pi$-conjugation topology, which results in distinctive electronic properties with both fundamental and practical implications. Although M"obius conjugation with phase inversion in atomic orbital (AO) basis is well-established for monocyclic systems, the extension of this understanding to double-stranded M"obius CNBs remains uncertain. This study thoroughly examines the simple H"uckel molecular orbital (SHMO) theory for describing the $pi$ electronic structures of M"obius CNBs. We demonstrate that the adjacency matrix for any M"obius CNB is isomorphism invariant under different placements of the sign inversion, ensuring identical SHMO results regardless of AO phase inversion location. Representative examples of M"obius CNBs, including the experimentally synthesized one, show that the H"uckel molecular orbitals (MOs) strikingly resemble the DFT-computed $pi$ MOs, which were obtained using a herein proposed technique based on the localization and re-delocalization of DFT canonical MOs. Interestingly, the lower-lying $pi$ MOs exhibit an odd number of nodal planes and are doubly quasidegenerate as a consequence of the phase inversion in M"obius macrocycles, contrasting with macrocyclic H"uckel systems. Coulson bond orders derived from SHMO theory correlate well with DFT-calculated Wiberg bond indices for all C-C bonds in tested M"obius CNBs. Additionally, a remarkable correlation is observed between HOMO-LUMO gaps obtained from the SHMO and GFN2-xTB calculations for a large number of topoisomers of M"obius CNBs. Thus, the SHMO model not only captures the essence of $pi$ electronic structure of M"obius CNBs, but also provides reliable quantitative predictions comparable to DFT results.
{"title":"Simple Hückel Molecular Orbital Theory for Möbius Carbon Nanobelts","authors":"Yang Wang","doi":"arxiv-2409.01689","DOIUrl":"https://doi.org/arxiv-2409.01689","url":null,"abstract":"The recently synthesized M\"obius carbon nanobelts (CNBs) have gained\u0000attention owing to their unique $pi$-conjugation topology, which results in\u0000distinctive electronic properties with both fundamental and practical\u0000implications. Although M\"obius conjugation with phase inversion in atomic\u0000orbital (AO) basis is well-established for monocyclic systems, the extension of\u0000this understanding to double-stranded M\"obius CNBs remains uncertain. This\u0000study thoroughly examines the simple H\"uckel molecular orbital (SHMO) theory\u0000for describing the $pi$ electronic structures of M\"obius CNBs. We demonstrate\u0000that the adjacency matrix for any M\"obius CNB is isomorphism invariant under\u0000different placements of the sign inversion, ensuring identical SHMO results\u0000regardless of AO phase inversion location. Representative examples of M\"obius\u0000CNBs, including the experimentally synthesized one, show that the H\"uckel\u0000molecular orbitals (MOs) strikingly resemble the DFT-computed $pi$ MOs, which\u0000were obtained using a herein proposed technique based on the localization and\u0000re-delocalization of DFT canonical MOs. Interestingly, the lower-lying $pi$\u0000MOs exhibit an odd number of nodal planes and are doubly quasidegenerate as a\u0000consequence of the phase inversion in M\"obius macrocycles, contrasting with\u0000macrocyclic H\"uckel systems. Coulson bond orders derived from SHMO theory\u0000correlate well with DFT-calculated Wiberg bond indices for all C-C bonds in\u0000tested M\"obius CNBs. Additionally, a remarkable correlation is observed\u0000between HOMO-LUMO gaps obtained from the SHMO and GFN2-xTB calculations for a\u0000large number of topoisomers of M\"obius CNBs. Thus, the SHMO model not only\u0000captures the essence of $pi$ electronic structure of M\"obius CNBs, but also\u0000provides reliable quantitative predictions comparable to DFT results.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"312 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190334","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}
Tamara Shaaban, Hanna Oher, Jean Aupiais, Julie Champion, André Severo Pereira Gomes, Claire Le Naour, Melody Maloubier, Florent Réal, Eric Renault, Xavier Rocquefelte, Bruno Siberchicot, Valérie Vallet, Rémi Maurice
The bond distance is the simplest and most obvious indicator of the nature of a given chemical bond. However, for rare chemistry, it may happen that it is not yet firmly established. In this communication, we will show that the formally-triple protactinium(V) mono-oxo bond is predicted longer than what was previously reported in the solid state and in solution, based on robust quantum mechanical calculations, supported by an extensive methodological study. Furthermore, additional calculations are used to demonstrate that the Pa-Ooxo bond of interest is more sensitive to complexation than the supposedly analogous U-Oyl ones, not only in terms of bond distance but also of finer bond descriptors associated with the effective bond multiplicity.
{"title":"Is the protactinium(V) mono-oxo bond weaker than what we thought?","authors":"Tamara Shaaban, Hanna Oher, Jean Aupiais, Julie Champion, André Severo Pereira Gomes, Claire Le Naour, Melody Maloubier, Florent Réal, Eric Renault, Xavier Rocquefelte, Bruno Siberchicot, Valérie Vallet, Rémi Maurice","doi":"arxiv-2409.01338","DOIUrl":"https://doi.org/arxiv-2409.01338","url":null,"abstract":"The bond distance is the simplest and most obvious indicator of the nature of\u0000a given chemical bond. However, for rare chemistry, it may happen that it is\u0000not yet firmly established. In this communication, we will show that the\u0000formally-triple protactinium(V) mono-oxo bond is predicted longer than what was\u0000previously reported in the solid state and in solution, based on robust quantum\u0000mechanical calculations, supported by an extensive methodological study.\u0000Furthermore, additional calculations are used to demonstrate that the Pa-Ooxo\u0000bond of interest is more sensitive to complexation than the supposedly\u0000analogous U-Oyl ones, not only in terms of bond distance but also of finer bond\u0000descriptors associated with the effective bond multiplicity.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190335","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}
Supercritical oxidation processes in jet-stirred reactors (JSR) have been modeled based on ideal gas assumption. This can lead to significant errors in or complete misinterpretation of modeling results. Therefore, this study newly developed a framework to model supercritical oxidation in JSRs by incorporating ab initio multi-body molecular potentials and high-order mixture Virial equation of state (EoS) into real-fluid conservation laws, with the related numerical strategies highlighted. With comparisons with the simulation results based on ideal EoS and the experimental data from high-pressure JSR experiments, the framework is proved to be a step forward compared to the existing JSR modeling frameworks. To reveal the real-fluid effects on the oxidation characteristics in jet-stirred reactors, simulations are further conducted at a wide range of conditions (i.e., temperatures from 500 to 1100 K and pressures from 100 to 1000 bar), the real-fluid effect is found to significantly promote fuel oxidation reactivity, especially at low temperatures, high pressures, and for mixtures with heavy fuels. The significant influences of real-fluid behaviors on JSR oxidation characteristics emphasize the need to adequately incorporate these effects for future modeling studies in JSR at high pressures, which has now been enabled through the framework proposed in this study.
{"title":"The first application of high-order Virial equation of state and ab initio multi-body potentials in modeling supercritical oxidation in jet-stirred reactors","authors":"Mingrui Wang, Ruoyue Tang, Xinrui Ren, Hongqing Wu, Ting Zhang, Song Cheng","doi":"arxiv-2409.01099","DOIUrl":"https://doi.org/arxiv-2409.01099","url":null,"abstract":"Supercritical oxidation processes in jet-stirred reactors (JSR) have been\u0000modeled based on ideal gas assumption. This can lead to significant errors in\u0000or complete misinterpretation of modeling results. Therefore, this study newly\u0000developed a framework to model supercritical oxidation in JSRs by incorporating\u0000ab initio multi-body molecular potentials and high-order mixture Virial\u0000equation of state (EoS) into real-fluid conservation laws, with the related\u0000numerical strategies highlighted. With comparisons with the simulation results\u0000based on ideal EoS and the experimental data from high-pressure JSR\u0000experiments, the framework is proved to be a step forward compared to the\u0000existing JSR modeling frameworks. To reveal the real-fluid effects on the\u0000oxidation characteristics in jet-stirred reactors, simulations are further\u0000conducted at a wide range of conditions (i.e., temperatures from 500 to 1100 K\u0000and pressures from 100 to 1000 bar), the real-fluid effect is found to\u0000significantly promote fuel oxidation reactivity, especially at low\u0000temperatures, high pressures, and for mixtures with heavy fuels. The\u0000significant influences of real-fluid behaviors on JSR oxidation characteristics\u0000emphasize the need to adequately incorporate these effects for future modeling\u0000studies in JSR at high pressures, which has now been enabled through the\u0000framework proposed in this study.","PeriodicalId":501304,"journal":{"name":"arXiv - PHYS - Chemical Physics","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142190211","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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