# Showing papers in "Chemical Physics Letters in 2004"

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TL;DR: In this article, a new hybrid exchange-correlation functional named CAM-B3LYP is proposed, which combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al.

Abstract: A new hybrid exchange–correlation functional named CAM-B3LYP is proposed. It combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al. [J. Chem. Phys., in press]. We demonstrate that CAM-B3LYP yields atomization energies of similar quality to those from B3LYP, while also performing well for charge transfer excitations in a dipeptide model, which B3LYP underestimates enormously. The CAM-B3LYP functional comprises of 0.19 Hartree–Fock (HF) plus 0.81 Becke 1988 (B88) exchange interaction at short-range, and 0.65 HF plus 0.35 B88 at long-range. The intermediate region is smoothly described through the standard error function with parameter 0.33.

10,882 citations

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Lund University

^{1}TL;DR: In this article, a shifted zeroth-order Hamiltonian is presented, which will be used in second-order multiconfigurational perturbation theory (CASPT2).

Abstract: A new shifted zeroth-order Hamiltonian is presented, which will be used in second-order multiconfigurational perturbation theory (CASPT2). The new approximation corrects for the systematic error of the original formulation, which led to an relative overestimate of the correlation energy for open shell system, resulting in too small dissociation and excitation energies. Errors in the D, values for 49 diatomic molecules have been reduced with more than 50%. Calculations on excited states of the N-2 and benzene molecules give a similar improvement. (C) 2004 Elsevier B.V. All rights reserved.

860 citations

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TL;DR: In this article, solid solutions of tungstate and molybdate scheelites doped with Eu 3+ ion have been synthesized by solid-state reactions.

Abstract: Solid solutions of tungstate and molybdate scheelites of formula NaLn(WO 4 ) 2 − x (MoO 4 ) x and NaY 1 − y Bi y (WO 4 ) 2 (Ln = Y, Gd) doped with Eu 3+ ion have been synthesized by solid-state reactions. Red luminescence is obtained in these samples on excitation either in the charge-transfer band or Eu 3+ levels. In particular, intense red emission is obtained by exciting at ∼394 nm using the sharp 7 F 0 → 5 L 6 line of Eu 3+ . These materials could find applications as red phosphors for white lighting devices utilizing GaN-based excitation in the near UV.

715 citations

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TL;DR: In this paper, the role of water in the hydration process of Ca 3 SiO 5 (C 3 S) cement is investigated, and accelerating effects of adding colloidal silica (CS) are established.

Abstract: The hydration process of Ca 3 SiO 5 (C 3 S) cement is investigated, and accelerating effects of adding colloidal silica (CS) are established. CS accelerates dissolution of the C 3 S phase, and renders a more rapid formation of the calcium–silicate–hydrate (C–S–H) binding phase. The role of water is demonstrated. Water evaporation correlates with the appearance of a sharp IR band at 3650 cm −1 signifying non-hydrogen bonded OH groups. Incomplete hydration results in Ca(OH) 2 precipitation. Suppression of water evaporation causes the 3650 cm −1 band to vanish. The Ca 2+ ions become incorporated in the C–S–H network, the formation of which is accelerated by CS.

562 citations

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TL;DR: In this paper, vertically aligned single-walled carbon nanotubes (SWNTs) with a few micrometer thickness were grown by catalytic chemical vapor deposition (CVD) on quartz substrates.

Abstract: Films of vertically aligned single-walled carbon nanotubes (SWNTs) with a few micrometer thickness were grown by catalytic chemical vapor deposition (CVD) on quartz substrates. Low-temperature CVD from ethanol was performed by using densely mono-dispersed Co–Mo catalyst of ≈1.0–2.0 nm prepared on quartz substrates by a dip-coating method. Continuous reduction of catalysts with Ar/H 2 (3% H 2 ) during CVD was essential for generating dense enough SWNTs with vertical alignment. Vertical alignment was clearly demonstrated by anisotropic optical absorption and transmission characteristics in addition to observations by FE-SEM, TEM and resonance Raman scattering.

544 citations

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TL;DR: In this paper, the authors studied NO 2 gas adsorption, diffusion, and reaction on a single walled carbon nanotube (SWNT) surface using ab initio simulations.

Abstract: NO 2 gas adsorption, diffusion, and reaction on a single walled carbon nanotube (SWNT) surface are studied using ab initio simulations. The small diffusion barriers of NO 2 on SWNT surface suggest that NO 2 molecules can produce NO and NO 3 through chemical reactions. From the estimation of diffusion barriers and binding energies of NO 2 , NO, and NO 3 on a SWNT surface, we show that NO 3 is the most likely long-lived species on SWNT. This finding enables us to explain why the experimental recovery times of NO 2 gas sensors have been measured to be as long as 12 h.

511 citations

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TL;DR: In this paper, the authors employ the Slater-type function as a geminal basis function to incorporate the inter-electron distance in explicitly correlated theory, and show that the use of the Slater type geminals confers numerical and computational advantages over the previous explicitly correlated methods.

Abstract: We employ the Slater-type function as a geminal basis function to incorporate the inter-electron distance in explicitly correlated theory. It is shown that the use of the Slater-type geminals confers numerical and computational advantages over the previous explicitly correlated methods. The performance of the resulting method is examined in some benchmark calculations at the second order Moller–Plesset perturbation theory. The results reveal that the Slater-type function is promising compared to the ordinary Gaussian-type geminals and linear r 12 function.

457 citations

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TL;DR: In this paper, a set of well-aligned ZnO nanorods were synthesized on a Si substrate at 600 °C by 193 nm pulsed laser ablation of a target in low pressures of oxygen using electron microscopy and X-ray diffraction.

Abstract: Arrays of well-aligned ZnO nanorods were synthesized on a Si substrate at 600 °C by 193 nm pulsed laser ablation of a ZnO target in low pressures of oxygen Electron microscopy and X-ray diffraction revealed highly c -axis aligned, ultra-thin, needle-like nanorods with tip diameters

421 citations

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TL;DR: In this paper, the role of vacancy defects in the fracture of carbon nanotubes under axial tension was investigated using density functional theory and semi-empirical methods, and molecular mechanics (MM) calculations with a Tersoff-Brenner potential.

Abstract: We present quantum mechanical calculations using density functional theory and semiempirical methods, and molecular mechanics (MM) calculations with a Tersoff–Brenner potential that explore the role of vacancy defects in the fracture of carbon nanotubes under axial tension. These methods show reasonable agreement, although the MM scheme systematically underestimates fracture strengths. One- and two-atom vacancy defects are observed to reduce failure stresses by as much as 26% and markedly reduce failure strains. Large holes – such as might be introduced via oxidative purification processes – greatly reduce strength, and this provides an explanation for the extant theoretical–experimental discrepancies. 2004 Published by Elsevier B.V.

370 citations

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TL;DR: In this paper, a modified standard approximation is proposed that involves expansion in the orthogonal complement to the span of orbital basis set (OBS) for linear R12 theories.

Abstract: Here we analyze the use of the resolution of the identity (RI) in approximating many-electron matrix elements in linear R12 theories. A modified standard approximation is proposed that involves expansion in the orthogonal complement to the span of orbital basis set (OBS). The new formulation is labeled complementary auxiliary basis set (CABS) approach. CABS MP2-R12 method has a smaller RI error vis-a-vis the standard ABS approach. Both ABS and CABS approaches are most accurate if the auxiliary basis includes OBS explicitly . The CABS approach found to be more numerically robust than the ABS counterpart.

356 citations

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TL;DR: In this article, single-walled carbon nanotubes (SWNTs) loaded with palladium (Pd) nanoparticles are used for detection of methane ranging from 6 to 100 ppm in air at room temperature.

Abstract: Single-walled carbon nanotubes (SWNTs) loaded with palladium (Pd) nanoparticles are used for detection of methane ranging from 6 to 100 ppm in air at room temperature. The Pd-SWNT nanosensors show advantages over conventional catalytic beads and metal oxide sensors for methane detection in terms of reduced size and power consumption by a factor of 100 and sensitivity by a factor of 10. A charge transfer sensing mechanism in which Pd attracts electrons from SWNTs to form a weakly bound complex Pd δ+ (CH 4 ) δ− is discussed. In addition, the elevated temperature and ultraviolet light effects on the sensor characteristics are also studied.

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TL;DR: In this paper, an efficient implementation of second order analytical derivatives (force constants) within density functional theory which applies to non-hybrid functionals has been presented, which results in pronounced reductions of computational work and implies insignificant losses in accuracy as is shown by extensive tests.

Abstract: We present an efficient implementation of second order analytical derivatives (force constants) within density functional theory which applies to non-hybrid functionals. The dominant step in force constant treatments concerns the solution of the coupled perturbed Kohn–Sham equations (CPKS). We employ an auxiliary basis expansion, the RI- J technique (resolution of the identity for the interelectronic Couomb energy J ), to accelerate the solution of the CPKS equations. This results in pronounced reductions of computational work and implies insignificant losses in accuracy as is shown by extensive tests. A force constant calculation of cyanocobalamin is reported as a demonstrative application.

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TL;DR: In this paper, an algorithm for finding pathways to transition states (TS) or dissociation channels (DC) from equilibrium structures (EQ) on the potential energy surface (PES) is presented.

Abstract: An algorithm for finding pathways to transition states (TS) or dissociation channels (DC) from equilibrium structures (EQ) on the potential energy surface (PES) is presented. The pathways around an EQ can be discovered at minima on the scaled hypersphere which would have a constant energy when the potentials are harmonic. Topographic maps including all TS, DC, and EQ were obtained for ab initio PES of H2O and HCHO in the MP2/3-21G level. The present scaled hypersphere search technique in combination with a downhill-walk algorithm enables us to make a topographic analysis of the PES for a given chemical composition.

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TL;DR: In this article, a neural network scheme for the construction of a continuous potential energy surface (PES) is presented, and the sticking probability of H2/K(2 · 2)/Pd(1 0 0) is determined by molecular dynamics simulations on the neural network PES and compared to results using an independent analytical interpolation.

Abstract: The determination of dissociative adsorption probabilities based on first-principles total-energy calculations requires a numerically efficient and accurate interpolation scheme in order to be able to run a sufficient number of trajectories. Here we present a neural network scheme for the construction of a continuous potential energy surface (PES). We illustrate the accuracy and efficiency of our method for H2 interacting with the (2 · 2) potassium covered Pd(1 0 0) surface. The sticking probability of H2/K(2 · 2)/ Pd(1 0 0) is determined by molecular dynamics simulations on the neural network PES and compared to results using an independent analytical interpolation. � 2004 Elsevier B.V. All rights reserved.

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TL;DR: In this paper, the influence of carbon nanotube (CNT) contents on electrical and rheological properties of CNTs-reinforced polypropylene (PP) composites was studied.

Abstract: The influence of carbon nanotube (CNT) contents on electrical and rheological properties of CNTs-reinforced polypropylene (PP) composites was studied. As a result, the volume resistivity of the composites was decreased with increasing the CNT content and the electrical percolation threshold was formed between 1 and 2 wt% CNTs, which were caused by the formation of conductive chains in the composites. And the viscosity of the composites was increased with the addition of CNTs, which was accompanied by an increase in elastic melt properties (G′). This could be explained by the higher aspect ratio of the CNTs. And the composites containing more than 2 wt% CNTs exhibited non-Newtonian curves at low frequency.

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TL;DR: In this paper, a diffractive optic was used to generate phase-locked three-pulse photon echo experiments for two-dimensional optical spectroscopy by using a Diffractive optic to generate the pulses required, and with careful introduction of the time delays between the pulses, achieved excellent passive phase-locking, approaching λ/100 at a wavelength of 540 nm.

Abstract: A novel technique has been developed to passively phase-lock heterodyne-detected three-pulse photon echo experiments for two-dimensional optical spectroscopy By using a diffractive optic to generate the pulses required, and with careful introduction of the time delays between the pulses, we achieve excellent passive phase-locking, approaching λ/100 at a wavelength of 540 nm The ability to generate phase-locked pulse pairs with independent time delays solves a long standing impediment for stable phase sensitive detection in true optical analogues of multi-dimensional nuclear magnetic resonance (NMR) techniques, and should be equally valuable in executing related multi-dimensional spectroscopies in the infrared

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TL;DR: In this paper, an extension of the Onsager model of exciton dissociation in the bulk of a disordered solid was used to determine the separation probability of geminate electron-hole pairs following exciton disociation by charge-transfer at a donor-acceptor interface.

Abstract: Using an extension of the Onsager model of exciton dissociation in the bulk of a disordered solid, we determine the separation probability of geminate electron–hole pairs following exciton dissociation by charge-transfer at a donor–acceptor interface. The donor–acceptor interface confines the electron and hole in their respective layers, leading to charge separation with a probability that is significantly higher than predicted by bulk theory. The model explains the surprisingly high carrier collection efficiencies observed in organic donor–acceptor photovoltaic cells, and correctly predicts the voltage-dependence of the photocurrent which differs substantially from that of conventional inorganic semiconductor p–n junctions and may ultimately limit the power conversion efficiency of organic donor–acceptor photovoltaic cells.

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TL;DR: In this article, a near-infrared fluorescence measurement was performed on single-walled carbon nanotubes (SWNTs) catalytically synthesized from alcohol under various experimental conditions (ACCVD) to determine the chirality distribution by measuring the fluorescence emitted from separated SWNTs as a function of excitation wavelength.

Abstract: Near-infrared fluorescence measurements were performed on single-walled carbon nanotubes (SWNTs) catalytically synthesized from alcohol under various experimental conditions (alcohol catalytic CVD method, ACCVD). The chirality distribution was determined by measuring the fluorescence emitted from separated SWNTs as a function of excitation wavelength. Compared with HiPco SWNTs, chiralities of the ACCVD sample were distributed predominantly in the higher chiral angle region, close to the so-called armchair structure. This tendency toward higher chiral angles was more pronounced for smaller diameter nanotubes. The reason for the armchair-rich chirality distribution is discussed based on the initial cap structure satisfying the ‘isolated pentagon rule’.

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TL;DR: In this article, 1-Butyl-3-methylimidazolium octyl sulfate was found to act as a surfactant above 0.031 M critical micelle concentration.

Abstract: Association of ionic liquids possessing n-octyl moiety either in the cation or in the anion has been studied in aqueous solution with conductivity and turbidity measurements as well as using 2-hydroxy-substituted Nile Red solvatochromic probe. 1-Butyl-3-methylimidazolium octyl sulfate was found to act as a surfactant above 0.031 M critical micelle concentration. In contrast, 1-methyl-3-octylimidazolium chloride produced inhomogeneous solution of larger aggregates, which were dissolved on the addition of more than 2:1 molar excess of sodium dodecyl sulfate (SDS) due to mixed micelle formation. Even small amount (<10 mM) of ionic liquids could markedly reduce the polarity of the Stern layer of SDS micelle.

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TL;DR: In this paper, the authors propose to calculate interatomic overlap populations, bond order indices and actual atomic valences from the results of ab initio quantum chemical calculations, in terms of "fuzzy" atoms, i.e., such divisions of the three-dimensional physical space into atomic regions in which the regions assigned to the individual atoms have no sharp boundaries but exhibit a continuous transition from one to another.

Abstract: Proper definitions are proposed to calculate interatomic overlap populations, bond order (multiplicity) indices and actual atomic valences from the results of ab initio quantum chemical calculations, in terms of ‘fuzzy’ atoms, i.e., such divisions of the three-dimensional physical space into atomic regions in which the regions assigned to the individual atoms have no sharp boundaries but exhibit a continuous transition from one to another. The results of test calculations are in agreement with the classical chemical notions, exhibit unexpectedly small basis sensitivity and do not depend too much on the selection of the weight function defining the actual division of the space into ‘fuzzy’ atomic regions. The scheme is applicable on both SCF and correlated levels of theory. A free program is available.

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TL;DR: In this paper, a multiconfiguration theory for electronic dynamics of molecules in an intense laser field is developed based on the Dirac-Frenkel time-dependent variational principle.

Abstract: A multiconfiguration theory for electronic dynamics of molecules in an intense laser field is developed based on the Dirac–Frenkel time-dependent variational principle. The equations of motion for spin–orbitals and configuration-interaction coefficients are explicitly given. Numerical calculations of electronic dynamics of a hydrogen molecule in an intense electronic field are performed as a practical application of the theory.

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TL;DR: In this article, the influence of sorbitol on the nanometer-scale morphology of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) is investigated by scanning-tunneling microscopy.

Abstract: The influence of sorbitol on the nanometer-scale morphology of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) is investigated by scanning–tunneling microscopy. In all investigated films relatively well-conducting PEDOT particles are observed, with typical sizes of 10–50 nm, that are embedded in a less conductive PSS matrix. Addition of sorbitol to the casting solution is found to enhance the clustering of the PEDOT particles into larger domains. The observed morphologies are correlated to the macroscopic conductivity of the films, using an intuitive model. In addition, the morphology in the top layer of the films was found to differ substantially from the bulk morphology.

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TL;DR: Molecular Dynamics Simulations of Water and Biomolecules with a Monte Carlo Constant Pressure Algorithm as discussed by the authors was used to simulate water and biomolecules in the simulation.

Abstract: Molecular Dynamics Simulations of Water and Biomolecules with a Monte Carlo Constant Pressure Algorithm

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TL;DR: The ability of 25 density functional theory (DFT) methods to treat Ne2, Ar2, CH4)2, C2H42 and three conformations of the benzene dimer was studied as discussed by the authors.

Abstract: The ability of 25 density functional theory (DFT) methods to treat Ne2, Ar2, (CH4)2, (C2H4)2 and three conformations of the benzene dimer was studied Only PW91, HTCH407, and VSXC predict all dimers to be bound However, VSXC strongly over-binds all of the complexes The DFTs predict repulsive potential energy surfaces (PES) for parallel benzene at large separations, in contrast to MP2 VSXC, B1B95, BB95, and BB1K, and to a lesser extent OLYP and O3LYP, are sensitive to the size of the integration grid used When used with standard grids, these methods predict multiple minima on one or more dimer PESs

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TL;DR: In this article, single-walled nitrogen doped nanotubes were prepared using two novel approaches in an arc discharge process, in which a nitrogen-rich precursor was introduced into the anode rods together with graphite and the catalysts.

Abstract: Single-walled nitrogen doped nanotubes were prepared using two novel approaches in an arc-discharge process. In both cases a nitrogen-rich precursor was introduced into the anode rods together with graphite and the catalysts. The nitrogen rich precursors were organic and inorganic, respectively. Both synthesis routes gave nanotubes with a nitrogen concentration of a maximum of 1%, determined using electron energy loss spectroscopy (EELS) coupled with transmission electron microscopy (TEM). All samples were characterized with scanning electron microscopy (SEM), TEM, and high-resolution transmission electron microscopy (HRTEM).

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TL;DR: In this paper, the application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated and it was shown that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations.

Abstract: The application of terahertz pulsed spectroscopy to polymorphic, liquid crystalline and amorphous forms of pharmaceutical compounds has been investigated. The different polymorphic forms of carbamazepine and enalapril maleate exhibit distinct terahertz absorbance spectra. In contrast to crystalline indomethacin and fenoprofen calcium, amorphous indomethacin and liquid crystalline fenoprofen calcium show no absorption modes, which is likely to be due to a lack of order. These findings suggest that the modes observed are due to crystalline phonon and possibly hydrogen-bonding vibrations. The large spectral differences between different forms of the compounds studied is evidence that terahertz pulsed spectroscopy is well-suited to distinguishing crystallinity differences in pharmaceutical compounds.

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TL;DR: Based on the novel stochastic methodology for describing quantum dynamics of dissipative systems [J. Shao, J. Chem. Phys. 120 (2004) 5053], a hierarchical approach is suggested and applied to the spin-boson model with Debye spectral density function as mentioned in this paper.

Abstract: Based on the novel stochastic methodology for describing quantum dynamics of dissipative systems [J. Shao, J. Chem. Phys. 120 (2004) 5053], a hierarchical approach is suggested and applied to the spin–boson model with Debye spectral density function. The algorithm to implement this deterministic technique is expounded and the numerical results for the spin–boson system are explained.

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TL;DR: In this paper, integrated carbon nanotube (CNT) electrodes for electric double layer capacitor (EDLC) were fabricated and the coin-type EDLC cells with directly grown CNT electrodes exhibited a rectangular cyclic voltammogram even at a scan rate of 1000 mV/s.

Abstract: Integrated carbon nanotube (CNT) electrodes for electric double layer capacitor (EDLC) were fabricated. CNTs were directly synthesized on the bulk Ni substrates by the plasma enhanced chemical vapor deposition of methane and hydrogen. No additional catalyst was necessary. The coin-type EDLC cells with directly grown CNT electrodes exhibited a rectangular cyclic voltammogram even at a scan rate of 1000 mV/s. Also, we could increase the capacitance of the CNT electrode from 38.7 to 207.3 F/g through surface treatment using ammonia plasma.

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TL;DR: In this article, the sequential structural changes of bundles of double-walled carbon nanotubes (DWNTs) as a function of heat treatment temperature were described. And the results demonstrate that DWNTs are much more stable than SWNTs, and their stability is comparable to that of MWNTs.

Abstract: We describe, for the first time, the sequential structural changes of bundles of double-walled carbon nanotubes (DWNTs) as a function of heat treatment temperature. DWNTs (inner diameters >0.9 nm) are structurally stable up to 2000 °C. Above 2100 °C, the outer walls of adjacent DWNTs start coalescing into large diameter tubes. At temperatures higher than 2100 °C, three different types of structures were observed: (a) large-diameter DWNTs; (b) multi-walled carbon nanotubes (MWNTs), and (c) flaky carbons. The results demonstrate that DWNTs are much more stable than SWNTs, and their stability is comparable to that of MWNTs.

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TL;DR: In this article, the potential energy surfaces are represented by a simple analytical form written as a sum of atom-bond interaction contributions, for which a new potential model, [ n ( x ), m ], is proposed.

Abstract: A method has been developed to describe the force field of atomic species interacting with hydrocarbon molecules, either aliphatic or aromatic, of use for molecular dynamics simulations. The potential energy surfaces are represented by a simple analytical form written as a sum of atom–bond interaction contributions, for which a new potential model, [ n ( x ), m ], is proposed. The prototypical systems, methane and benzene, interacting with rare gases He, Ne, Ar, Kr and Xe, are analyzed as test cases. The method appears suitable for extensions to more complex systems, including modifications for treating ion–ion and ion–molecule interactions.