Bond lengths in free molecules of buckminsterfullerene, c60, from gas-phase electron diffraction

Theoretical and computational methods for tip- and surface-enhanced Raman scattering

Raman spectroscopy is a versatile tool for acquiring molecular structure information. The incorporation of plasmonic fields has significantly enhanced the sensitivity and resolution of surface-enhanced Raman scattering (SERS) and tip-enhanced Raman spectroscopy (TERS). The strong spatial confinement effect of plasmonic fields has challenged the conventional Raman theory, in which a plane wave approximation for the light has been adopted. In this review, we comprehensively survey the progress of a generalized theory for SERS and TERS in the framework of effective field Hamiltonian (EFH). With this approach, all characteristics of localized plasmonic fields can be well taken into account. By employing EFH, quantitative simulations at the first-principles level for state-of-the-art experimental observations have been achieved, revealing the underlying intrinsic physics in the measurements. The predictive power of EFH is demonstrated by several new phenomena generated from the intrinsic spatial, momentum, time, and energy structures of the localized plasmonic field. The corresponding experimental verifications are also carried out briefly. A comprehensive computational package for modeling of SERS and TERS at the first-principles level is introduced. Finally, we provide an outlook on the future developments of theory and experiments for SERS and TERS.

Single-Pole Polarization Models: Rapid Evaluation of Electron Affinities of Solvated-Electron and Superatomic Molecular Anionic States

We propose a single-parameter effective one-particle potential, termed the single-pole exchange-correlation (1p-XC), to rapidly evaluate electron affinities (EAs) of nonvalence electronic states of molecular clusters and nanoassemblies. The model combines exact-exchange and the random phase approximation (RPA) correlation potential with a single-pole approximation to model the frequency-dependent polarization function. It captures long-range static and dynamic-frequency effects in the correlation potential, with mean absolute errors of 0.06 eV for EAs of hydrated- and ammoniated-electron clusters with EA values in the range 0.24-1.77 eV. The 1p-XC approximation enables EA estimation with a computational wall-time similar to that of hybrid functionals. The model also provides a compressed-basis, which significantly reduces the rank of higher-level parameter-free one-particle Hamiltonians and further simplifies the computation of EAs. The compressed-basis approach is used to model the hybridization of superatomic molecular states of (C60)2- and (C60)3-, thereby verifying previous model Hamiltonian studies.

The Stokes-Einstein-Sutherland Equation at the Nanoscale Revisited

The Stokes-Einstein-Sutherland (SES) equation is at the foundation of statistical physics, relating a particle's diffusion coefficient and size with the fluid viscosity, temperature, and the boundary condition for the particle-solvent interface. It is assumed that it relies on the separation of scales between the particle and the solvent, hence it is expected to break down for diffusive transport on the molecular scale. This assumption is however challenged by a number of experimental studies showing a remarkably small, if any, violation, while simulations systematically report the opposite. To understand these discrepancies, analytical ultracentrifugation experiments are combined with molecular simulations, both performed at unprecedented accuracies, to study the transport of buckminsterfullerene C60 in toluene at infinite dilution. This system is demonstrated to clearly violate the conditions of slow momentum relaxation. Yet, through a linear response to a constant force, the SES equation can be recovered in the long time limit with no more than 4% uncertainty both in experiments and in simulations. This nonetheless requires partial slip on the particle interface, extracted consistently from all the data. These results, thus, resolve a long-standing discussion on the validity and limits of the SES equation at the molecular scale.

Synergy of semiempirical models and machine learning in computational chemistry

Catalyzed by enormous success in the industrial sector, many research programs have been exploring data-driven, machine learning approaches. Performance can be poor when the model is extrapolated to new regions of chemical space, e.g., new bonding types, new many-body interactions. Another important limitation is the spatial locality assumption in model architecture, and this limitation cannot be overcome with larger or more diverse datasets. The outlined challenges are primarily associated with the lack of electronic structure information in surrogate models such as interatomic potentials. Given the fast development of machine learning and computational chemistry methods, we expect some limitations of surrogate models to be addressed in the near future; nevertheless spatial locality assumption will likely remain a limiting factor for their transferability. Here, we suggest focusing on an equally important effort-design of physics-informed models that leverage the domain knowledge and employ machine learning only as a corrective tool. In the context of material science, we will focus on semi-empirical quantum mechanics, using machine learning to predict corrections to the reduced-order Hamiltonian model parameters. The resulting models are broadly applicable, retain the speed of semiempirical chemistry, and frequently achieve accuracy on par with much more expensive ab initio calculations. These early results indicate that future work, in which machine learning and quantum chemistry methods are developed jointly, may provide the best of all worlds for chemistry applications that demand both high accuracy and high numerical efficiency.

Introducing a novel C50N10 azafullerene with chained nitrogen atoms on a buckyball pole: structure, stability, vibration, and electronic properties

CONTEXT

Fullerenes are of high significance due to their unique chemical properties and various applications in technology, particularly materials science, drug delivery, electronics, and nanoelectronics. In the recent years, many attempts have been focused to introduce new heteroatom-doped fullerenes having advanced chemical properties and tunable electronic traits, which make them a potential candidate for application in many branches of sciences. In this study, a novel C₅₀N₁₀ azafullerene with a fascinating structure of chained nitrogen atoms on a buckyball pole, with different electronic and optical properties compared to its other analogs, is introduced and trace of N-N substructures on the surface of C₆₀ fullerene cage is investigated. For this molecule, four structural isomers including 3 structures with chain N atoms on a fullerene buckyball pole (NP isomers) and one isomer with separated N atoms (SN isomer) have been studied. All isomers have been studied with and without symmetry constraints, and the symmetry influence on the structure and stability of each isomer has been investigated. Although the studied NP structures have lower stability than the SN isomer, some reasons (such as their more all-carbon hexagonal rings, breaking some of their N-N bonds for partial opening of the cage and creating bigger rings in order to get rid of the unfavorable strain, as well as decreasing the N-N lone pair repulsions) lead to the acceptable stability of these structures with the bonded N atoms. The results of atomization energy and vibrational frequency calculations indicate that isomers with the bonded N atoms have acceptable stabilities and do not decompose into their constituent components. Investigation on the structural parameters demonstrates important roles of the number of all-carbon hexagonal rings, the number of N-N junction, and the molecule symmetry in the stability of the structures with the bonded N atoms. Study on the electronic and optical properties indicates that the target structures exhibit high electronic polarizability, relatively small HOMO/LUMO gap, high first- and second-order hyperpolarizability, and also large third-order nonlinear optical properties.

METHODS

All calculations have been performed using Gaussian G09 software using density functional theory (DFT) approach. Three-parameter Beck hybrid exchange functional (B3) hybridized with nonlocal correlation functional of Lee, Yang, and Parr (LYP) has been employed as the level of DFT calculations. All optimizations have been performed at double-zeta polarized (DZP) split valence 6-31G(d,p) and also at split valence TZP 6-311G(d,p) basis sets. The global minimum structures have been confirmed by frequency calculations at the same level of optimizations. The natural bond orbital (NBO) analyses, frontier orbital surfaces imaging, atomic charges, and charge transfer analyses have been achieved by GenNBO program package.

Computational investigation on the geometry and electronic structures and absorption spectra of metal-porphyrin-oligo- phenyleneethynylenes-[60] fullerene triads

In this work, we focus our attention on the influence of 2nd-row transition metals on the structural geometries, electronic structures, and absorption characteristics of porphyrin linked with the C₆₀ fullerene with oligo-p-phenyleneethynylenes (MP-C₆₀-oligo-PPEs) compounds. The DFT/B3PW91-D3 and CAM-B3LYP-D3/6-31G (d) calculations revealed that various metals embedded within the porphyrin moiety give different bridge conformations and different HOMO-LUMO energy levels. We calculate the UV-Vis spectra and absorption parameters using the time-dependent ZINDO/S approach. Our findings indicate that all the compounds have enhanced absorptions in the visible light range, and their molecular orbital energies adopt the condition of sensitizers. However, all of the complexes except down spin states exhibit considerably charge spatial separation. The results suggest that the ZnP-C₆₀-oligo-PPEs triad can meet the necessary conditions of the sensitizer of dye-sensitized solar cells (DSSCs) in comparison with other counterparts and could be an optimum triad compound for potential application in photovoltaic devices.

A multiscale ONIOM study of the buckminsterfullerene (C60) Diels-Alder reaction: from model design to reaction path analysis

The hybrid ONIOM (Our own N-layered Integrated molecular Orbital and molecular Mechanics) formalism is employed to investigate the Diels-Alder reaction of the buckminsterfullerene C₆₀. Our computations suggest that the ONIOM2(M06-2X/6-31G(d): SVWN/STO-3G) model, enclosing both the diene and the pyracyclene fragment of C60 in the higher-layer, provides a reasonable trade-off between accuracy and computational cost as it comes to predicting reaction energetics. Moreover, the frontier molecular orbital (FMO) theory and activation strain model (ASM) are jointly relied on to rationalize the effect of -OH and -CN substituents on the activation barrier of this reaction. Finally, reaction paths are scrutinized to get insight into the various forces underpinning the process of cycloadduct formation.

A new route for enantio-sensitive structure determination by photoelectron scattering on molecules in the gas phase

Combination of Coulomb explosion imaging, molecular frame diffraction imaging, and ab initio computations provide a route for enantio-sensitive structure determination.

Artificial intelligence-enhanced quantum chemical method with broad applicability

High-level quantum mechanical (QM) calculations are indispensable for accurate explanation of natural phenomena on the atomistic level. Their staggering computational cost, however, poses great limitations, which luckily can be lifted to a great extent by exploiting advances in artificial intelligence (AI). Here we introduce the general-purpose, highly transferable artificial intelligence-quantum mechanical method 1 (AIQM1). It approaches the accuracy of the gold-standard coupled cluster QM method with high computational speed of the approximate low-level semiempirical QM methods for the neutral, closed-shell species in the ground state. AIQM1 can provide accurate ground-state energies for diverse organic compounds as well as geometries for even challenging systems such as large conjugated compounds (fullerene C60) close to experiment. This opens an opportunity to investigate chemical compounds with previously unattainable speed and accuracy as we demonstrate by determining geometries of polyyne molecules-the task difficult for both experiment and theory. Noteworthy, our method's accuracy is also good for ions and excited-state properties, although the neural network part of AIQM1 was never fitted to these properties.

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes

While the blocking barrier (U eff) and blocking temperature (T B) for "Dysprocenium" SIMs have been increased beyond liquid N2 temperature, device fabrication of these molecules remains a challenge as low-coordinate Ln3+ complexes are very unstable. Encapsulating the lanthanide ion inside a cage such as a fullerene (called endohedral metallofullerene or EMF) opens up a new avenue leading to several Ln@EMF SMMs. The ab initio CASSCF calculations play a pivotal role in identifying target metal ions and suitable cages in this area. Encouraged by our earlier prediction on Ln2@C79N, which was verified by experiments, here we have undertaken a search to enhance the exchange coupling in this class of molecules beyond the highest reported value. Using DFT and ab initio calculations, we have studied a series of Gd2@C2n (30 ≤ 2n ≤ 80), where an antiferromagnetic J Gd⋯Gd of -43 cm-1 was found for a stable Gd2@C38-D 3h cage. This extremely large and exceptionally rare 4f⋯4f interaction results from a direct overlap of 4f orbitals due to the confinement effect. In larger cages such as Gd2@C60 and Gd2@C80, the formation of two centre-one-electron (2c-1e-) Gd-Gd bonds is perceived. This results in a radical formation in the fullerene cage leading to its instability. To avoid this, we have studied heterofullerenes where one of the carbon atoms is replaced by a nitrogen atom. Specifically, we have studied Ln2@C59N and Ln2@C79N, where strong delocalisation of the electron yields a mixed valence-like behaviour. This suggests a double-exchange (B) is operational, and CASSCF calculations yield a B value of 434.8 cm-1 and resultant J Gd-rad of 869.5 cm-1 for the Gd2@C59N complex. These parameters are found to be two times larger than the world-record J reported for Gd2@C79N. Further ab initio calculations reveal an unprecedented U cal of 1183 and 1501 cm-1 for Dy2@C59N and Tb2@C59N, respectively. Thus, this study offers strong exchange coupling as criteria for new generation SMMs as the existing idea of enhancing the blocking barrier via crystal field modulation has reached its saturation point.

Local energy decomposition analysis and molecular properties of encapsulated methane in fullerene (CH4@C60)

Methane has been successfully encapsulated within cages of C₆₀ fullerene, which is an appropriate model system to study confinement effects. Its chemistry and physics are also relevant for theoretical model descriptions. Here we provide insights into intermolecular interactions and predicted spectroscopic responses of the CH₄@C₆₀ complex and compared them with results from other methods and with data from the literature. Local energy decomposition analysis (LED) within the domain-based local pair natural orbital coupled cluster singles, doubles, and perturbative triples (DLPNO-CCSD(T)) framework was used, and an efficient protocol for studies of endohedral complexes of fullerenes is proposed. This approach allowed us to assess energies in relation to electronic and geometric preparation, electrostatics, exchange, and London dispersion for the CH₄@C₆₀ endohedral complex. The calculated stabilization energy of CH₄ inside the C₆₀ fullerene was -13.5 kcal mol^-1 and its magnitude was significantly larger than the latent heat of evaporation of CH₄. Evaluation of vibrational frequencies and polarizabilities of the CH₄@C₆₀ complex revealed that the infrared (IR) and Raman bands of the endohedral CH₄ were essentially "silent" due to the dielectric screening effect of C₆₀, which acted as a molecular Faraday cage. Absorption spectra in the UV-vis domain and ionization potentials of C₆₀ and CH₄@C₆₀ were predicted. They were almost identical. The calculated ¹H/¹³C NMR shifts and spin-spin coupling constants were in very good agreement with experimental data. In addition, reference DLPNO-CCSD(T) interaction energies for complexes with noble gases (Ng@C₆₀; Ng = He, Ne, Ar, Kr) were calculated. The values were compared with those derived from supramolecular MP2/SCS-MP2 calculations and estimates with London-type formulas by Pyykkö and coworkers [Phys. Chem. Chem. Phys., 2010, 12, 6187-6203], and with values derived from DFT-based symmetry-adapted perturbation theory (DFT-SAPT) by Hesselmann & Korona [Phys. Chem. Chem. Phys., 2011, 13, 732-743]. Selected points at the potential energy surface of the endohedral He₂@C₆₀ trimer were considered. In contrast to previous theoretical attempts with the DFT/MP2/SCS-MP2/DFT-SAPT methods, our calculations at the DLPNO-CCSD(T) level of theory predicted the He₂@C₆₀ trimer to be thermodynamically stable, which is in agreement with experimental observations.

Vibrational spectra of La@C60 and Ce@C60 endohedral fullerenes: Influence of spin state multiplicity

Endohedral fullerenes with paramagnetic encapsulated atoms are new magnetic materials of interest for numerous applications from medicine to quantum computers. An important phenomenon with endohedral fullerenes is the appearance of new vibrational frequencies not associated with empty fullerenes. The vibrational spectra of the lanthanide endohedral fullerenes La@C₆₀ and Ce@C₆₀ in various spin states are calculated using the density functional method. Most of the spectral lines lie in the 300-1600 cm^-1range, and their intensities change dramatically depending on the molecule's symmetry and spin state, which are determined by the encapsulated lanthanide atom. The average frequency shift of the carbon cage vibrations caused by spin transition is only 5 cm^-1. The calculated frequencies of the coupled "metal-carbon cage" vibrations of the lanthanide endohedral fullerenes La@C₆₀ and Ce@C₆₀ in various spin states lie in the 10-170 cm^-1range. The computational results for both the frequencies and intensities of the metal-cage modes depend considerably on the spin state. The changes in these vibrational modes are due to the changes in the molecular symmetry and the metal-carbon bond lengths. Such dependence can be used as a basis for controlling the spin state of metallofullerenes by measuring the vibration frequencies in the far-infrared zone, which could be important for nanoelectronics and quantum informatics.

Substructural Approach for Assessing the Stability of Higher Fullerenes

This review describes the most significant published results devoted to the study of the nature of the higher fullerenes stability, revealing of correlations between the structural features of higher fullerene molecules and the possibility of their producing. A formalization of the substructure approach to assessing the stability of higher fullerenes is proposed, which is based on a detailed analysis of the main structural features of fullerene molecules. The developed substructure approach, together with the stability of the substructures constituting the fullerene molecule, helps to understand deeper the features of the electronic structure of fullerenes.

Size-dependent polarizabilities and van der Waals dispersion coefficients of fullerenes from large-scale complex polarization propagator calculations

While the anomalous non-additive size-dependencies of static dipole polarizabilities and van der Waals C₆ dispersion coefficients of carbon fullerenes are well established, the widespread reported scalings for the latter (ranging from N^2.2 to N^2.8) call for a comprehensive first-principles investigation. With a highly efficient implementation of the linear complex polarization propagator, we have performed Hartree-Fock and Kohn-Sham density functional theory calculations of the frequency-dependent polarizabilities for fullerenes consisting of up to 540 carbon atoms. Our results for the static polarizabilities and C₆ coefficients show scalings of N^1.2 and N^2.2, respectively, thereby deviating significantly from the previously reported values obtained with the use of semi-classical/empirical methods. Arguably, our reported values are the most accurate to date as they represent the first ab initio or first-principles treatment of fullerenes up to a convincing system size.

Heterofullerene MC59 (M = B, Si, Al) as Potential Carriers for Hydroxyurea Drug Delivery

As a representative nanomaterial, C₆₀ and its derivatives have drawn much attention in the field of drug delivery over the past years, due to their unique geometric and electronic structures. Herein, the interactions of hydroxyurea (HU) drug with the pristine C₆₀ and heterofullerene MC₅₉ (M = B, Si, Al) were investigated using the density functional theory calculations. The geometric and electronic properties in terms of adsorption configuration, adsorption energy, Hirshfeld charge, frontier molecular orbitals, and charge density difference are calculated. In contrast to pristine C₆₀, it is found that HU molecule is chemisorbed on the BC₅₉, SiC₅₉, and AlC₅₉ molecules with moderate adsorption energy and apparent charge transfer. Therefore, heterofullerene BC₅₉, SiC₅₉, and AlC₅₉ are expected to be promising carriers for hydroxyurea drug delivery.

Open-shell nature of non-IPR fullerene С40: isomers 29 (C2) and 40 (Td)

It is well-known that the small non-IPR fullerenes C_n (n < 60) are highly unstable and that is why they cannot be obtained as empty cages. However, they become stable as exohedral or endohedral derivatives. In this report, the molecular structures of non-IPR isomers 29 (C₂) and 40 (T_d) of fullerene C₄₀ are investigated using a semiempirical approach developed earlier for higher fullerenes. Quantum-chemical calculations (DFT) show that isomers 29 (C₂) and 40 (T_d) have open-shell structures. The distributions of single, double, and delocalized π-bonds in the isomer molecules in question are presented for the first time as well as their molecular formulas. It is found unusual for higher fullerenes chain of π-bonds passing through some cycles. Identified features in the structures of small fullerene molecules can be predictive of the ability to their synthesis as derivatives and will assist in their structure determination.

Caged-electron states and split-electron states in the endohedral alkali C60

The low-lying electronic states of neutral X@C60 (X = Li, Na, K, Rb) have been computed and analyzed by employing state-of-the-art high level many-electron methods. Apart from the common charge-separated states, well known to be present in endohedral fullerenes, one non-charge-separated state has been found in each of the investigated systems. In Li@C60 and Na@C60, the non-charge-separated state is a caged-electron state already discussed before for Li@C60. This indicates that the application of this low-lying state of Li@C60 discussed before is also applicable for Na@C60. In K@C60 and Rb@C60, the electronic radial distribution analysis shows that this hitherto unknown non-charge-separated state possesses a different nature from that of a caged-electron state.

Structure of C60F36: A Gas-Phase Electron Diffraction and Quantum Chemical Computational Study of a Remarkably Distorted Fluorofullerene

The equilibrium molecular structure of the gaseous fluorofullerene C₆₀F₃₆ has been determined for the first time by the electron diffraction method with the use of quantum chemical calculations up to the RI-MP2/def2-TZVPP level of theory. Vibrational amplitudes and quadratic and cubic force constants were calculated by density functional theory methods. It was found that the sample under study consists of the isomer of C₁ symmetry, 81(4)%, with a small amount of the isomer of C₃ symmetry, in good accordance with HPLC-MS (atmospheric pressure photoionization), HPLC-UV/vis, and NMR spectroscopic data. The presence of the isomer of T symmetry, up to 5%, cannot be completely excluded. Theoretical structural parameters of the C₆₀F₃₆ molecule were compared with those of the C₆₀F₄₈ molecule. Relative to C₆₀, the C₆₀F₃₆ molecule has a remarkably distorted carbon cage because of steric, electrostatic, and orbital interactions. This results in the longest carbon-carbon bond (1.671 Å) found in free molecules. In particular, about the longest FC-CF bond, the dihedral angle is only around 20°, which leads to the very short nonbonded distance between electronegative vicinal fluorine atoms (2.531 Å) that is much shorter than the sum of van der Waals radii of fluorine atoms (2.94 Å). A natural bond orbital analysis revealed that strong n_π(F) → σ*(FC-CF) interactions delocalize the lone pair of π-type at the fluorine atoms into the antibonding orbital of the FC-CF bond. This hyperconjugation results in additional elongation of FC-CF bonds.

Low pressure gas electron diffraction: An experimental setup and case studies

Principles of low pressure gas electron diffraction are introduced. An experimental setup has been constructed for measuring the electron diffraction patterns of gaseous samples at pressures below 10^-3 mbar. Test measurements have been performed for benzoic acid at T = 287 K corresponding to a vapor pressure of the substance P = 2 × 10^-4 mbar, for iodoform CHI₃ at T = 288 K (P = 4 × 10^-4 mbar), and for carbon tetraiodide CI₄ at T = 290 K (P = 1 × 10^-4 mbar). Due to the low experimental temperature, thermal decomposition of CI₄ has been prevented, which was unavoidable in previous classical measurements at higher temperatures. From the obtained data, the molecular structures have been successfully refined. The most important semi-empirical equilibrium molecular parameters are r_e(C_ar-C_ar)_av = 1.387(5) Å in benzoic acid, r_e(C-I) = 2.123(3) Å in iodoform, and r_e(C-I) = 2.133(7) Å in carbon tetraiodide. The determined parameters showed consistency with the theoretically predicted values. A critical comparison with the results of the earlier investigations has also been done.

Fine structure in the solution state 13C-NMR spectrum of C60 and its endofullerene derivatives

The ¹³C NMR spectrum of fullerene C₆₀ in solution displays two small "side peaks" on the shielding side of the main ¹³C peak, with integrated intensities of 1.63% and 0.81% of the main peak. The two side peaks are shifted by -12.6 ppb and -20.0 ppb with respect to the main peak. The side peaks are also observed in the ¹³C NMR spectra of endofullerenes, but with slightly different shifts relative to the main peak. We ascribe the small additional peaks to minor isotopomers of C₆₀ containing two adjacent ¹³C nuclei. The shifts of the additional peaks are due to a secondary isotope shift of the ¹³C resonance caused by the substitution of a ¹²C neighbour by ¹³C. Two peaks are observed since the C₆₀ structure contains two different classes of carbon-carbon bonds with different vibrational characteristics. The 2 : 1 ratio of the side peak intensities is consistent with the known structure of C₆₀. The origin and intensities of the ¹³C side peaks are discussed, together with an analysis of the ¹³C solution NMR spectrum of a ¹³C-enriched sample of C₆₀, which displays a relatively broad ¹³C NMR peak due to a statistical distribution of ¹³C isotopes. The spectrum of ¹³C-enriched C₆₀ is analyzed by a Monte Carlo simulation technique, using a theorem for the second moment of the NMR spectrum generated by J-coupled spin clusters.

Icosadeltahedral Geometry of Geodesic Domes, Fullerenes and Viruses: A Tutorial on the T-Number

The Caspar–Klug (CK) classification of viruses is discussed by parallel examination of geometry of icosahedral geodesic domes, fullerenes, and viruses. The underlying symmetry of all structures is explained and thoroughly visually represented. Euler’s theorem on polyhedra is used to calculate the number of vertices, edges, and faces in domes, number of atoms, bonds, and pentagonal and hexagonal rings in fullerenes, and number of proteins and protein–protein contacts in viruses. The T-number, the characteristic for the CK classification, is defined and discussed. The superposition of fullerene and dome designs is used to obtain a representation of a CK virus with all the proteins indicated. Some modifications of the CK classifications are sketched, including elongation of the CK blueprint, fusion of two CK blueprints, dodecahedral view of the CK shapes, and generalized CK designs without a clearly visible geometry of the icosahedron. These are compared to cases of existing viruses.

Crystal symmetry determination in electron diffraction using machine learning

Electron backscatter diffraction (EBSD) is one of the primary tools for crystal structure determination. However, this method requires human input to select potential phases for Hough-based or dictionary pattern matching and is not well suited for phase identification. Automated phase identification is the first step in making EBSD into a high-throughput technique. We used a machine learning-based approach and developed a general methodology for rapid and autonomous identification of the crystal symmetry from EBSD patterns. We evaluated our algorithm with diffraction patterns from materials outside the training set. The neural network assigned importance to the same symmetry features that a crystallographer would use for structure identification.

Functionalization and antioxidant activity of polyaniline–fullerene hybrid nanomaterials: a theoretical investigation

Functionalized fullerene is one of the most advantageous nanotechnologies to develop novel materials for potential biomedical applications. In this study, we applied the ONIOM-GD3 approach to explore the nucleophilic addition reaction mechanism between polyaniline (emeraldine and leucoemeraldine forms) and fullerene. Potential energy surfaces were also analyzed to predict the predominantly formed products of the functionalized reaction. The themoparameters, such as bond dissociation enthalpy (BDE), ionization energy (IE), and electron affinity (EA), characterized by two mechanisms HAT and SET, were used to evaluate the antioxidant activities of the selected compounds. Moreover, the calculated HOMO, LUMO, and DOS results indicate that the electronic structures of polyaniline–fullerene were significantly affected by the presence of fullerene. The computational results show that C60-L1 seems to be the best antioxidant following the SET mechanism.

Functionalized fullerene is one of the most advantageous nanotechnologies to develop novel materials for potential biomedical applications.

Rovibrational quantum state resolution of the C60 fullerene

The unique physical properties of buckminsterfullerene, C₆₀, have attracted intense research activity since its original discovery. Total quantum state-resolved spectroscopy of isolated C₆₀ molecules has been of particularly long-standing interest. Such observations have, to date, been unsuccessful owing to the difficulty in preparing cold, gas-phase C₆₀ in sufficiently high densities. Here we report high-resolution infrared absorption spectroscopy of C₆₀ in the 8.5-micron spectral region (1180 to 1190 wave number). A combination of cryogenic buffer-gas cooling and cavity-enhanced direct frequency comb spectroscopy has enabled the observation of quantum state-resolved rovibrational transitions. Characteristic nuclear spin statistical intensity patterns confirm the indistinguishability of the 60 carbon-12 atoms, while rovibrational fine structure encodes further details of the molecule's rare icosahedral symmetry.

Structural studies of carbons by neutron and x-ray scattering

Carbon can have many different forms and the characterisation of structural features on a length scale of 1 Å to 10 μm is important in defining its physical and chemical properties for the various forms. The use of either electro-magnetic (x-ray) or particle (neutron) beams plays an important role in determining these characteristics. In this paper, we review the various techniques that are used to determine the structural features by experimental means and how the data are processed to give the required information in a suitable form for detailed analysis by computer simulation. Diffraction methods are used for studies of the atomic arrangement and small-angle scattering techniques are used for studies of microporosity in the sample materials. The experimental data obtained from a wide range of different carbon materials are considered and how these results can be used as a basis for modelling the structures in a quantitative manner is also considered. This information underpins their use as active components in a wide range of functional materials.