P. S. Koliogiannis, M. Vikiaris, C. Panos, V. Petousis, M. Veselsky, Ch. C. Moustakidis
In a remarkable study by M. Gleiser and N. Jiang (Phys. Rev. D {bf 92}, 044046, 2015), the authors demonstrated that the stability regions of neutron stars, within the framework of the simple Fermi gas model, and self-gravitating configurations of complex scalar field (boson stars) with various self couplings, obtained through traditional perturbation methods, correlates with critical points of the configurational entropy with an accuracy of a few percent. Recently, P. Koliogiannis textit{et al.} (Phys. Rev. D {bf 107}, 044069 2023) found that while the minimization of the configurational entropy generally anticipates qualitatively the stability point for neutron stars and quark stars, this approach lacks universal validity. In this work, we aim to further elucidate this issue by seeking to reconcile these seemingly contradictory findings. Specifically, we calculate the configurational entropy of bosonic and fermionic systems, described by interacting Fermi and Boson gases, respectively, that form compact objects stabilized by gravity. We investigate whether the minimization of configurational entropy coincides with the stability point of the corresponding compact objects. Our results indicate a strong correlation between the stability points predicted by configurational entropy and those obtained through traditional methods, with the accuracy of this correlation showing a slight dependence on the interaction strength. Consequently, the stability of compact objects, composed of components obeying Fermi or Boson statistics, can alternatively be assessed using the concept of configurational entropy.
在M. Gleiser和N. Jiang（Phys. Rev. D {bf 92},044046,2015）的一项引人注目的研究中，作者证明了在简单费米气体模型的框架内，通过传统的扰动方法得到的中子星的稳定区域，以及具有各种自耦合的复杂标量场（玻色子星）的自引力构型，与构型熵的临界点的相关性精确到了百分之几。最近，P. Koliogiannis （P. Koliogiannis et al.｝(Phys. Rev. D {bf 107},044069 2023)发现，虽然构型熵的最小化一般可以定性地预测中子星和夸克星的稳定点，但这种方法缺乏普遍有效性。在这项研究中，我们试图通过调和这些看似矛盾的发现来进一步阐明这一问题。具体来说，我们计算了玻色系统和费米系统的构型熵，这两个系统分别由相互作用的费米气和玻色气描述，它们形成了由引力稳定的紧凑物体。我们研究了构型熵的最小化是否与相应紧凑物体的稳定点相吻合。我们的研究结果表明，由构型熵预测的稳定点与通过传统方法获得的稳定点之间存在很强的相关性，这种相关性的准确性略微依赖于相互作用的强度。
{"title":"Configurational entropy and stability conditions of fermion and boson stars","authors":"P. S. Koliogiannis, M. Vikiaris, C. Panos, V. Petousis, M. Veselsky, Ch. C. Moustakidis","doi":"arxiv-2409.02803","DOIUrl":"https://doi.org/arxiv-2409.02803","url":null,"abstract":"In a remarkable study by M. Gleiser and N. Jiang (Phys. Rev. D {bf 92},\u0000044046, 2015), the authors demonstrated that the stability regions of neutron\u0000stars, within the framework of the simple Fermi gas model, and self-gravitating\u0000configurations of complex scalar field (boson stars) with various self\u0000couplings, obtained through traditional perturbation methods, correlates with\u0000critical points of the configurational entropy with an accuracy of a few\u0000percent. Recently, P. Koliogiannis textit{et al.} (Phys. Rev. D {bf 107},\u0000044069 2023) found that while the minimization of the configurational entropy\u0000generally anticipates qualitatively the stability point for neutron stars and\u0000quark stars, this approach lacks universal validity. In this work, we aim to\u0000further elucidate this issue by seeking to reconcile these seemingly\u0000contradictory findings. Specifically, we calculate the configurational entropy\u0000of bosonic and fermionic systems, described by interacting Fermi and Boson\u0000gases, respectively, that form compact objects stabilized by gravity. We\u0000investigate whether the minimization of configurational entropy coincides with\u0000the stability point of the corresponding compact objects. Our results indicate\u0000a strong correlation between the stability points predicted by configurational\u0000entropy and those obtained through traditional methods, with the accuracy of\u0000this correlation showing a slight dependence on the interaction strength.\u0000Consequently, the stability of compact objects, composed of components obeying\u0000Fermi or Boson statistics, can alternatively be assessed using the concept of\u0000configurational entropy.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204112","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}
D. M. Khodachenko, R. Lucrezi, P. N. Ferreira, M. Aichhorn, C. Heil
In this work, we present a method to reconstruct real-frequency properties from analytically continued causal Green's functions within the framework of Migdal-Eliashberg (ME) theory for superconductivity. ME theory involves solving a set of coupled equations self-consistently in imaginary frequency space, but to obtain experimentally measurable properties like the spectral function and quasiparticle density of states, it is necessary to perform an analytic continuation to real frequency space. Traditionally, the ME Green's function is decomposed into three fundamental complex functions, which are analytically continued independently. However, these functions do not possess the causal properties of Green's functions, complicating or even preventing the application of standard methods such as Maximum Entropy. Our approach overcomes these challenges, enabling the use of various analytic continuation techniques that were previously impractical. We demonstrate the effectiveness of this method by combining it with Nevanlinna analytic continuation to achieve accurate real-frequency results for ME theory, which are directly comparable to experimental data, with applications highlighted for the superconductors MgB$_2$ and LaBeH$_8$.
{"title":"Nevanlinna Analytic Continuation for Migdal-Eliashberg Theory","authors":"D. M. Khodachenko, R. Lucrezi, P. N. Ferreira, M. Aichhorn, C. Heil","doi":"arxiv-2409.02737","DOIUrl":"https://doi.org/arxiv-2409.02737","url":null,"abstract":"In this work, we present a method to reconstruct real-frequency properties\u0000from analytically continued causal Green's functions within the framework of\u0000Migdal-Eliashberg (ME) theory for superconductivity. ME theory involves solving\u0000a set of coupled equations self-consistently in imaginary frequency space, but\u0000to obtain experimentally measurable properties like the spectral function and\u0000quasiparticle density of states, it is necessary to perform an analytic\u0000continuation to real frequency space. Traditionally, the ME Green's function is\u0000decomposed into three fundamental complex functions, which are analytically\u0000continued independently. However, these functions do not possess the causal\u0000properties of Green's functions, complicating or even preventing the\u0000application of standard methods such as Maximum Entropy. Our approach overcomes\u0000these challenges, enabling the use of various analytic continuation techniques\u0000that were previously impractical. We demonstrate the effectiveness of this\u0000method by combining it with Nevanlinna analytic continuation to achieve\u0000accurate real-frequency results for ME theory, which are directly comparable to\u0000experimental data, with applications highlighted for the superconductors\u0000MgB$_2$ and LaBeH$_8$.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"70 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204113","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 propose a simple estimator that allows to calculate the absolute value of a system's partition function from a finite sampling of its canonical ensemble. The estimator utilizes a volume correction term to compensate the effect that the finite sampling cannot cover the whole configuration space. As a proof of concept, the estimator is applied to calculate the partition function for several model systems, and the results are compared with the numerically exact solutions. Excellent agreement is found, demonstrating that a solution for an efficient calculation of partition functions is possible.
{"title":"A Partition Function Estimator","authors":"Ying-Chih Chiang, Frank Otto, Jonathan W. Essex","doi":"arxiv-2409.02538","DOIUrl":"https://doi.org/arxiv-2409.02538","url":null,"abstract":"We propose a simple estimator that allows to calculate the absolute value of\u0000a system's partition function from a finite sampling of its canonical ensemble.\u0000The estimator utilizes a volume correction term to compensate the effect that\u0000the finite sampling cannot cover the whole configuration space. As a proof of\u0000concept, the estimator is applied to calculate the partition function for\u0000several model systems, and the results are compared with the numerically exact\u0000solutions. Excellent agreement is found, demonstrating that a solution for an\u0000efficient calculation of partition functions is possible.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204115","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}
Emanuel F. Teixeira, Carine P. Beatrici, Heitor C. M. Fernandes, Leonardo G. Brunnet
Cell cortex contraction is essential for shaping cells, enabling movement, ensuring proper division, maintaining tissue integrity, guiding development, and responding to mechanical signals - all critical for the life and health of multicellular organisms. Differential contractions in cell membranes, particularly when cells of different types interact, play a crucial role in the emergence of segregation. In this study, we introduce a model where rings composed of active particles interact through differential membrane contraction within a specified cutoff distance. We demonstrate that segregation arises solely from differential contraction, with the activity of the rings functioning similarly to an effective temperature. Additionally, we observed that segregation involves cluster fusion-diffusion process. However, the decay exponent of the segregation parameter we found is close to $lambda sim -1/3$, which differs from the $lambda sim -1/4$ predicted by previous theoretical approaches and simulations.
{"title":"Segregation in binary mixture with differential contraction among active rings","authors":"Emanuel F. Teixeira, Carine P. Beatrici, Heitor C. M. Fernandes, Leonardo G. Brunnet","doi":"arxiv-2409.02814","DOIUrl":"https://doi.org/arxiv-2409.02814","url":null,"abstract":"Cell cortex contraction is essential for shaping cells, enabling movement,\u0000ensuring proper division, maintaining tissue integrity, guiding development,\u0000and responding to mechanical signals - all critical for the life and health of\u0000multicellular organisms. Differential contractions in cell membranes,\u0000particularly when cells of different types interact, play a crucial role in the\u0000emergence of segregation. In this study, we introduce a model where rings\u0000composed of active particles interact through differential membrane contraction\u0000within a specified cutoff distance. We demonstrate that segregation arises\u0000solely from differential contraction, with the activity of the rings\u0000functioning similarly to an effective temperature. Additionally, we observed\u0000that segregation involves cluster fusion-diffusion process. However, the decay\u0000exponent of the segregation parameter we found is close to $lambda sim -1/3$,\u0000which differs from the $lambda sim -1/4$ predicted by previous theoretical\u0000approaches and simulations.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"85 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204111","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}
With significant advances in classifying and cataloguing topological matter, the focus of topological physics has shifted towards quantum control, particularly the creation and manipulation of topological phases of matter. Floquet engineering, the concept of tailoring a system by periodic fields, offers a powerful tool to manipulate electronic properties of condensed systems, and even to create exotic non-equilibrium topological states that are impossibly present in equilibrium scenarios. In this perspective, we give a brief review of recent progress in theoretical investigations of Floquet engineering topological states from effective models towards realistic materials. We show that light irradiation can realize various desired topological states through the introduction of symmetry breaking, such as first- and higher-order Weyl fermions, quadrupole topological insulator with periodic driving and disorder, quantum anomalous Hall effects with a tunable Chern number, as well as beyond. Moreover, based on first-principles calculations and Floquet theorem, we show several realistic material candidates proposed as potential hosts for promising Floquet topological states, facilitating their verification in experiments. We believe that our perspective on Floquet engineering of topological states will advance further studies of rich exotic light-induced phenomena in condensed matter physics.
{"title":"Perspective: Floquet engineering topological states from effective models towards realistic materials","authors":"Fangyang Zhan, Rui Chen, Zhen Ning, Da-Shuai Ma, Da-Shuai Ma, Dong-Hui Xu, Rui Wang","doi":"arxiv-2409.02774","DOIUrl":"https://doi.org/arxiv-2409.02774","url":null,"abstract":"With significant advances in classifying and cataloguing topological matter,\u0000the focus of topological physics has shifted towards quantum control,\u0000particularly the creation and manipulation of topological phases of matter.\u0000Floquet engineering, the concept of tailoring a system by periodic fields,\u0000offers a powerful tool to manipulate electronic properties of condensed\u0000systems, and even to create exotic non-equilibrium topological states that are\u0000impossibly present in equilibrium scenarios. In this perspective, we give a\u0000brief review of recent progress in theoretical investigations of Floquet\u0000engineering topological states from effective models towards realistic\u0000materials. We show that light irradiation can realize various desired\u0000topological states through the introduction of symmetry breaking, such as\u0000first- and higher-order Weyl fermions, quadrupole topological insulator with\u0000periodic driving and disorder, quantum anomalous Hall effects with a tunable\u0000Chern number, as well as beyond. Moreover, based on first-principles\u0000calculations and Floquet theorem, we show several realistic material candidates\u0000proposed as potential hosts for promising Floquet topological states,\u0000facilitating their verification in experiments. We believe that our perspective\u0000on Floquet engineering of topological states will advance further studies of\u0000rich exotic light-induced phenomena in condensed matter physics.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"172 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204109","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}
Yuanqing Wang, Kenichiro Takaba, Michael S. Chen, Marcus Wieder, Yuzhi Xu, John Z. H. Zhang, Kuang Yu, Xinyan Wang, Linfeng Zhang, Daniel J. Cole, Joshua A. Rackers, Joe G. Greener, Peter Eastman, Stefano Martiniani, Mark E. Tuckerman
A force field as accurate as quantum mechanics (QM) and as fast as molecular mechanics (MM), with which one can simulate a biomolecular system efficiently enough and meaningfully enough to get quantitative insights, is among the most ardent dreams of biophysicists -- a dream, nevertheless, not to be fulfilled any time soon. Machine learning force fields (MLFFs) represent a meaningful endeavor towards this direction, where differentiable neural functions are parametrized to fit ab initio energies, and furthermore forces through automatic differentiation. We argue that, as of now, the utility of the MLFF models is no longer bottlenecked by accuracy but primarily by their speed (as well as stability and generalizability), as many recent variants, on limited chemical spaces, have long surpassed the chemical accuracy of $1$ kcal/mol -- the empirical threshold beyond which realistic chemical predictions are possible -- though still magnitudes slower than MM. Hoping to kindle explorations and designs of faster, albeit perhaps slightly less accurate MLFFs, in this review, we focus our attention on the design space (the speed-accuracy tradeoff) between MM and ML force fields. After a brief review of the building blocks of force fields of either kind, we discuss the desired properties and challenges now faced by the force field development community, survey the efforts to make MM force fields more accurate and ML force fields faster, envision what the next generation of MLFF might look like.
一个像量子力学（QM）一样精确、像分子力学（MM）一样快速的力场，可以让人们足够高效、足够有意义地模拟生物分子系统，从而获得定量的洞察力，这是生物物理学家最迫切的梦想之一--然而，这个梦想不会很快实现。机器学习力场（MLFFs）是朝着这个方向迈出的有意义的一步，它将可微分的神经功能参数化，以适应自始能量，并通过自动微分进一步施加力。我们认为，到目前为止，MLFF 模型的实用性不再受限于准确性，而主要受限于速度（以及稳定性和普适性），因为在有限的化学空间上，许多最新的变体早已超过了 1 美元千卡/摩尔的化学准确性--这是有可能进行现实化学预测的经验阈值--尽管速度仍然比 MM 慢很多。为了帮助探索和设计更快、但准确度可能略低的 ML 力场，在本综述中，我们将重点关注 MM 力场和 ML 力场之间的设计空间（速度-准确度权衡）。在简要回顾了这两种力场的构件之后，我们讨论了力场开发界所期望的特性和目前面临的挑战，调查了为使 MM 力场更精确、ML 力场更快速所做的努力，并设想了下一代 MLFF 的样子。
{"title":"On the design space between molecular mechanics and machine learning force fields","authors":"Yuanqing Wang, Kenichiro Takaba, Michael S. Chen, Marcus Wieder, Yuzhi Xu, John Z. H. Zhang, Kuang Yu, Xinyan Wang, Linfeng Zhang, Daniel J. Cole, Joshua A. Rackers, Joe G. Greener, Peter Eastman, Stefano Martiniani, Mark E. Tuckerman","doi":"arxiv-2409.01931","DOIUrl":"https://doi.org/arxiv-2409.01931","url":null,"abstract":"A force field as accurate as quantum mechanics (QM) and as fast as molecular\u0000mechanics (MM), with which one can simulate a biomolecular system efficiently\u0000enough and meaningfully enough to get quantitative insights, is among the most\u0000ardent dreams of biophysicists -- a dream, nevertheless, not to be fulfilled\u0000any time soon. Machine learning force fields (MLFFs) represent a meaningful\u0000endeavor towards this direction, where differentiable neural functions are\u0000parametrized to fit ab initio energies, and furthermore forces through\u0000automatic differentiation. We argue that, as of now, the utility of the MLFF\u0000models is no longer bottlenecked by accuracy but primarily by their speed (as\u0000well as stability and generalizability), as many recent variants, on limited\u0000chemical spaces, have long surpassed the chemical accuracy of $1$ kcal/mol --\u0000the empirical threshold beyond which realistic chemical predictions are\u0000possible -- though still magnitudes slower than MM. Hoping to kindle\u0000explorations and designs of faster, albeit perhaps slightly less accurate\u0000MLFFs, in this review, we focus our attention on the design space (the\u0000speed-accuracy tradeoff) between MM and ML force fields. After a brief review\u0000of the building blocks of force fields of either kind, we discuss the desired\u0000properties and challenges now faced by the force field development community,\u0000survey the efforts to make MM force fields more accurate and ML force fields\u0000faster, envision what the next generation of MLFF might look like.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204138","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}
Analytic continuation (AC) from imaginary-time Green's function to spectral function is essential in the numerical analysis of dynamical properties in quantum many-body systems. However, this process faces a fundamental challenge: it is an ill-posed problem, leading to unstable spectra against the noise in the Green's function. This instability is further complicated in multi-orbital systems with hybridization between spin-orbitals, where off-diagonal Green's functions yield a spectral matrix with off-diagonal elements, necessitating the matrix's semi-positive definiteness to satisfy the causality. We propose an advanced AC method using sparse modeling for multi-orbital systems, which reduces the effect of noise and ensures the matrix's semi-positive definiteness. We demonstrate the effectiveness of this approach by contrasting it with the conventional sparse modeling method, focusing on handling Green's functions with off-diagonal elements, thereby demonstrating our proposed method's enhanced stability and precision.
{"title":"Robust analytic continuation using sparse modeling approach imposed by semi-positive definiteness for multi-orbital systems","authors":"Yuichi Motoyama, Hiroshi Shinaoka, Junya Otsuki, Kazuyoshi Yoshimi","doi":"arxiv-2409.01509","DOIUrl":"https://doi.org/arxiv-2409.01509","url":null,"abstract":"Analytic continuation (AC) from imaginary-time Green's function to spectral\u0000function is essential in the numerical analysis of dynamical properties in\u0000quantum many-body systems. However, this process faces a fundamental challenge:\u0000it is an ill-posed problem, leading to unstable spectra against the noise in\u0000the Green's function. This instability is further complicated in multi-orbital\u0000systems with hybridization between spin-orbitals, where off-diagonal Green's\u0000functions yield a spectral matrix with off-diagonal elements, necessitating the\u0000matrix's semi-positive definiteness to satisfy the causality. We propose an\u0000advanced AC method using sparse modeling for multi-orbital systems, which\u0000reduces the effect of noise and ensures the matrix's semi-positive\u0000definiteness. We demonstrate the effectiveness of this approach by contrasting\u0000it with the conventional sparse modeling method, focusing on handling Green's\u0000functions with off-diagonal elements, thereby demonstrating our proposed\u0000method's enhanced stability and precision.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204134","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}
Nima Ghafari Cherati, I. Abdolhosseini Sarsari, Arsalan Hashemi, Tapio Ala-Nissila
For many materials, Raman spectra are intricately structured and provide valuable information about compositional stoichiometry and crystal quality. Here we use density-functional theory calculations, mass approximation, and the Raman intensity weighted $Gamma$-point density of state approach to analyze Raman scattering and vibrational modes in zincblende, wurtzite, and hexagonal BX (X = N, P, and As) structures. The influence of crystal structure and boron isotope disorder on Raman line shapes is examined. Our results demonstrate that long-range Coulomb interactions significantly influence the evolution of Raman spectra in cubic and wurtzite BN compounds. With the evolution of the compositional rate from $^{11}$B to $^{10}$B, a shift toward higher frequencies, as well as the maximum broadening and asymmetry of the Raman peaks, is expected around the 1:1 ratio. The calculated results are in excellent agreement with the available experimental data. This study serves as a guide for understanding how crystal symmetry and isotope disorder affect phonons in BX compounds, which are relevant to quantum single-photon emitters, heat management, and crystal quality assessments.
{"title":"Boron Isotope Effects on Raman Scattering in Bulk BN, BP, and BAs: A Density-Functional Theory Study","authors":"Nima Ghafari Cherati, I. Abdolhosseini Sarsari, Arsalan Hashemi, Tapio Ala-Nissila","doi":"arxiv-2409.01671","DOIUrl":"https://doi.org/arxiv-2409.01671","url":null,"abstract":"For many materials, Raman spectra are intricately structured and provide\u0000valuable information about compositional stoichiometry and crystal quality.\u0000Here we use density-functional theory calculations, mass approximation, and the\u0000Raman intensity weighted $Gamma$-point density of state approach to analyze\u0000Raman scattering and vibrational modes in zincblende, wurtzite, and hexagonal\u0000BX (X = N, P, and As) structures. The influence of crystal structure and boron\u0000isotope disorder on Raman line shapes is examined. Our results demonstrate that\u0000long-range Coulomb interactions significantly influence the evolution of Raman\u0000spectra in cubic and wurtzite BN compounds. With the evolution of the\u0000compositional rate from $^{11}$B to $^{10}$B, a shift toward higher\u0000frequencies, as well as the maximum broadening and asymmetry of the Raman\u0000peaks, is expected around the 1:1 ratio. The calculated results are in\u0000excellent agreement with the available experimental data. This study serves as\u0000a guide for understanding how crystal symmetry and isotope disorder affect\u0000phonons in BX compounds, which are relevant to quantum single-photon emitters,\u0000heat management, and crystal quality assessments.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204133","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}
Zhan Tong Zhang, Máté Visegrádi, Jiří J. L. Vaníček
Hagedorn wavepackets have been used with local harmonic approximation to partially capture the anharmonic effects on single vibronic level (SVL) spectra in model potentials. To make the Hagedorn approach practical for realistic anharmonic polyatomic molecules, here we combine local harmonic Hagedorn wavepacket dynamics with on-the-fly ab initio dynamics. We then test this method by computing the SVL fluorescence spectra of difluorocarbene, a small, floppy molecule with a very anharmonic potential energy surface. Our time-dependent approach obtains the emission spectra of all initial vibrational levels from a single anharmonic semiclassical wavepacket trajectory without the need to fit individual anharmonic vibrational wavefunctions and to calculate the Franck--Condon factors for all vibronic transitions. We show that, whereas global harmonic models are inadequate for CF$_2$, the spectra computed with the on-the-fly local harmonic Hagedorn wavepacket dynamics agree well with experimental data, especially for low initial excitations.
{"title":"On-the-Fly Ab Initio Hagedorn Wavepacket Dynamics: Single Vibronic Level Fluorescence Spectra of Difluorocarbene","authors":"Zhan Tong Zhang, Máté Visegrádi, Jiří J. L. Vaníček","doi":"arxiv-2409.01862","DOIUrl":"https://doi.org/arxiv-2409.01862","url":null,"abstract":"Hagedorn wavepackets have been used with local harmonic approximation to\u0000partially capture the anharmonic effects on single vibronic level (SVL) spectra\u0000in model potentials. To make the Hagedorn approach practical for realistic\u0000anharmonic polyatomic molecules, here we combine local harmonic Hagedorn\u0000wavepacket dynamics with on-the-fly ab initio dynamics. We then test this\u0000method by computing the SVL fluorescence spectra of difluorocarbene, a small,\u0000floppy molecule with a very anharmonic potential energy surface. Our\u0000time-dependent approach obtains the emission spectra of all initial vibrational\u0000levels from a single anharmonic semiclassical wavepacket trajectory without the\u0000need to fit individual anharmonic vibrational wavefunctions and to calculate\u0000the Franck--Condon factors for all vibronic transitions. We show that, whereas\u0000global harmonic models are inadequate for CF$_2$, the spectra computed with the\u0000on-the-fly local harmonic Hagedorn wavepacket dynamics agree well with\u0000experimental data, especially for low initial excitations.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204118","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 mineral schreibersite, e.g., Fe$_3$P, is commonly found in iron-rich meteorites and could have served as an abiotic phosphorus source for prebiotic chemistry. However, atomistic calculations of its degradation chemistry generally require quantum simulation approaches, which can be too computationally cumbersome to study sufficient time and length scales for this process. In this regard, we have created a computationally efficient semi-empirical quantum Density Functional Tight Binding (DFTB) model for iron and phosphorus-containing materials by adopting an existing semi-automated workflow that represents many-body interactions by linear combinations of Chebyshev polynomials. We have utilized a relatively small training set to optimize a DFTB model that is accurate for schreibersite physical and chemical properties, including its bulk properties, surface energies, and water absorption. We then show that our model shows strong transferability to several iron phosphide solids as well as multiple allotropes of iron metal. Our resulting DFTB parameterization will allow us to interrogate schreibersite aqueous decomposition at longer time and length scales than standard quantum approaches, allowing for investigations of its role in prebiotic chemistry on early Earth.
{"title":"Creation of an Fe$_3$P Schreibersite Density Functional Tight Binding Model for Astrobiological Simulations","authors":"Riccardo Dettori, Nir Goldman","doi":"arxiv-2409.01884","DOIUrl":"https://doi.org/arxiv-2409.01884","url":null,"abstract":"The mineral schreibersite, e.g., Fe$_3$P, is commonly found in iron-rich\u0000meteorites and could have served as an abiotic phosphorus source for prebiotic\u0000chemistry. However, atomistic calculations of its degradation chemistry\u0000generally require quantum simulation approaches, which can be too\u0000computationally cumbersome to study sufficient time and length scales for this\u0000process. In this regard, we have created a computationally efficient\u0000semi-empirical quantum Density Functional Tight Binding (DFTB) model for iron\u0000and phosphorus-containing materials by adopting an existing semi-automated\u0000workflow that represents many-body interactions by linear combinations of\u0000Chebyshev polynomials. We have utilized a relatively small training set to\u0000optimize a DFTB model that is accurate for schreibersite physical and chemical\u0000properties, including its bulk properties, surface energies, and water\u0000absorption. We then show that our model shows strong transferability to several\u0000iron phosphide solids as well as multiple allotropes of iron metal. Our\u0000resulting DFTB parameterization will allow us to interrogate schreibersite\u0000aqueous decomposition at longer time and length scales than standard quantum\u0000approaches, allowing for investigations of its role in prebiotic chemistry on\u0000early Earth.","PeriodicalId":501369,"journal":{"name":"arXiv - PHYS - Computational Physics","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142204132","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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