Simulating the structural diversity of carbon clusters across the planar-to-fullerene transition

Bonnin, M.A.; Falvo, Cyril; Calvo, F.; Pino, T.; Parneix, P.

doi:10.1103/physreva.99.042504

Cited by 19 publications

(37 citation statements)

References 86 publications

(116 reference statements)

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“…The structural diversity of size-selected carbon clusters was explored in our previous work (Bonnin et al 2019;Dubosq et al 2019) and classified according to dedicated order parameters, from which the asphericity β and the ratio of sp 2 hybridization among carbon atoms were found to be the most insightful. Based on these parameters, four main families could be identified: cages, planar polyaromatics (PPAs; also called flakes), pretzels, and branched structures.…”

Section: Building Up the Populations Of Isomersmentioning

confidence: 99%

“…1a. An initial sample of about 100 000 structures was determined for each of the four families from a force field exploration (Bonnin et al 2019) followed by local optimization (Dubosq et al 2019) at the level of self-consistent charge density functional tight-binding (SCC-DFTB) (Elstner et al 1998). Among these structures, between about 5000 and 12 000 (8-17%) were selected for electronic spectroscopy in order to save computational burden (see Fig.…”

Section: Building Up the Populations Of Isomersmentioning

confidence: 99%

“…The main goal of the present investigation is to assess the possible contribution of these various isomers to the UV bump and to evaluate their relevance as a component of interstellar dust. This work follows on an earlier effort in which the structural diversity itself was characterized (Bonnin et al 2019) and its correlation with the infrared (IR) response evaluated in comparison with the spectra measured in planetary nebulae (Dubosq et al 2019). Here we employ the same samples, but focus on the optical response in the UV-visible range, using appropriate but consistent methodologies for addressing electronic excitations in large databases containing hundreds of thousands of structures.…”

Section: Introductionmentioning

confidence: 99%

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Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

Dubosq

Calvo

Rapacioli

et al. 2020

A&A

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Context. The UV bump observed in the interstellar medium extinction curve of galaxies has been assigned to π → π⋆ transitions within the sp2 conjugated network of carbon grains. These grains are commonly thought to be graphitic particles or polycyclic aromatic hydrocarbons. However, questions are still open regarding the shape and degree of amorphization of these particles, which could account for the variations in the 2175 Å astronomical bump. Optical spectra of graphitic and onion-like carbon structures were previously obtained from dielectric constant calculations based on oscillating dipole models. In the present study, we compute the optical spectra of entire populations of carbon clusters using an explicit quantum description of their electronic structure for each individual isomer. Aims. Our aim is to determine the optical spectra of pure carbon clusters Cn=24,42,60 sorted into structural populations according to specific order parameters, namely asphericity and sp2 fraction, and to correlate these order parameters to the spectral features of the band in the region of the UV bump. Our comparison involves data measured for the astronomical UV bump as well as experimental spectra of carbon species formed in laboratory flames. Methods. The individual spectrum of each isomer is determined using the time-dependent density functional tight-binding method. The final spectrum for a given population is obtained by averaging the individual spectra for all isomers of a given family. Our method allows for an explicit description of particle shape, as well as structural and electronic disorder with respect to purely graphitic structures. Results. The spectra of the four main populations of cages, flakes, pretzels, and branched structures (Dubosq et al. 2019, A&A, 625, L11) all display strong absorption in the 2–8 eV domain, mainly due to π → π⋆ transitions. The absorption features, however, differ from one family to another and our quantum modeling indicates that the best candidates for the interstellar UV bump at 217.5 nm are cages and then flakes, while the opposite trend is found for the carbonaceous species formed in flame experiments; the other two families of pretzels and branched structures play a lesser role in both cases. Conclusions. Our quantum modeling shows the potential contribution of carbon clusters with a high fraction of conjugated sp2 atoms to the astronomical UV bump and to the spectrum of carbonaceous species formed in flames. While astronomical spectra are better accounted for using rather spherical isomers such as cages, planar flake structures are involved as a much greater component in flame experiments. Interestingly, these flake isomers have been proposed as likely intermediates in the formation mechanisms leading to buckminsterfullerene, which was recently detected in space. This study, although restricted here to the case of pure carbon clusters, will be extended towards several directions of astronomical relevance. In particular, the ability of the present approach to deal with large-scale molecular systems at an explicit quantum level of electronic structure and its transferable character towards different charge states and the possible presence of heteroatoms makes it the method of choice to address the important case of neutral and ionic hydrogenated compounds.

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Section: Building Up the Populations Of Isomersmentioning

confidence: 99%

Section: Building Up the Populations Of Isomersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

Dubosq

Calvo

Rapacioli

et al. 2020

A&A

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“…We chose C 24 as its PES exploration followed by structural and spectral analysis was achieved in our previous works 18,27 . In those studies, the PES exploration was performed using parallel tempering molecular dynamics (PTMD) 41 with the REBO force field 42 , followed by local SCC-DFTB optimization. Despite the fact that, in both studies [Ref.…”

Section: Benchmark Of the Ga/dftb Algorithm And Definition Of Structu...mentioning

confidence: 99%

Hydrogenation of C$_{24}$ carbon clusters : structural diversity and energetic properties

Pla,

Dubosq,

Rapacioli

et al. 2021

Preprint

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This work aims at exploring the potential energy surfaces of C 24 H n=0, 6,12,18,24 up to 20-25 eV using the genetic algorithm in combination with the density functional based tight binding (DFTB) potential. The structural diversity of the non fragmented structures was analysed using order parameters which were chosen as the number of 5 or 6 member rings and the asphericity constant β. The most abundant and lowest energy population was found to correspond to a flakes population, constituted of isomers of variable shapes possessing a large number of 5 or 6-carbon rings. This population is characterized by a larger number of spherical isomers when n H /n C increases. Simultaneously, the fraction of the pretzels population constituted of spherical isomers possessing fewer 5 or 6 carbon ring cycles increases. For all hydrogenation rates, the fraction of cages population, possessing the largest number of 5 or 6-carbon rings remains extremely minor while the branched population, characterized by the smallest number of 5 or 6-carbon rings, is the highest energy population for all n H /n C ratios. For all C 24 H n=0,6,12,18,24 clusters, a detailed study of the evolution of the carbon ring size distribution as a function of energy clearly shows that the stability is correlated to the number of 6-carbon rings. A similar study for hybridization sp n (n=1-3) shows that the number of sp 1 carbon atoms increases with energy while globally the number of sp 3 carbon atoms increases with n H /n C . The average values of the ionization potentials of all populations, obtained at the self-consistent charge DFTB level, were found to decrease when n H /n C increases, ranging from 7.9 eV down to 6.4 eV. We correlated this trend to geometric and electronic factors, in particular to carbon atoms hybridization sp n (n=1-3). These results are of astrophysical interest as they should be taken into account in astrophysical models especially regarding the role of carbonaceous species in the gas ionization.

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“…Modeling such PES within a quantum approach rapidly becomes computationally prohibitive, therefore empirical analytic expressions are usually employed to describe the interactions between the particles composing the clusters. Examples of these potentials are the Lennard-Jones (Jones and Ingham, 1925), Morse (Morse, 1929), and REBO (Brenner et al, 2002; Kosimov et al, 2010; Bonnin et al, 2019; Jiang et al, 2019; Lin et al, 2019) potentials, the latter being a more complex one which has gained prominence due to its applicability to describe graphene potential energy surfaces (Jiang et al, 2019; Lin et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

A New Genetic Algorithm Approach Applied to Atomic and Molecular Cluster Studies

Silva

Belchior

2019

Front. Chem.

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A new procedure is suggested to improve genetic algorithms for the prediction of structures of nanoparticles. The strategy focuses on managing the creation of new individuals by evaluating the efficiency of operators (o1, o2,…,o13) in generating well-adapted offspring. This is done by increasing the creation rate of operators with better performance and decreasing that rate for the ones which poorly fulfill the task of creating favorable new generation. Additionally, several strategies (thirteen at this level of approach) from different optimization techniques were implemented on the actual genetic algorithm. Trials were performed on the general case studies of 26 and 55-atom clusters with binding energy governed by a Lennard-Jones empirical potential with all individuals being created by each of the particular thirteen operators tested. A 18-atom carbon cluster and some polynitrogen systems were also studied within REBO potential and quantum approaches, respectively. Results show that our management strategy could avoid bad operators, keeping the overall method performance with great confidence. Moreover, amongst the operators taken from the literature and tested herein, the genetic algorithm was faster when the generation of new individuals was carried out by the twist operator, even when compared to commonly used operators such as Deaven and Ho cut-and-splice crossover. Operators typically designed for basin-hopping methodology also performed well on the proposed genetic algorithm scheme.

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Simulating the structural diversity of carbon clusters across the planar-to-fullerene transition

Cited by 19 publications

References 86 publications

Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump

Hydrogenation of C$_{24}$ carbon clusters : structural diversity and energetic properties

A New Genetic Algorithm Approach Applied to Atomic and Molecular Cluster Studies

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