ABINIT: First-principles approach to material and nanosystem properties

The coupling between electronic and nuclear degrees of freedom in low-dimensional, nanoscale systems plays a fundamental role in shaping many of their properties. Here, we report the disentanglement of axial and radial expansions of carbon nanotubes, and the direct role of electronic and vibrational excitations in determining such expansions. With subpicosecond and subpicometer resolutions, structural dynamics were explored by monitoring changes of the electron diffraction following an ultrafast optical excitation, whereas the transient behavior of the charge distribution was probed by time-resolved, electron-energy-loss spectroscopy. Our experimental results, and supporting density functional theory calculations, indicate that a population of the excited carriers in the antibonding orbitals of the nanotube walls drives a transient axial deformation in ∼1 ps; this deformation relaxes on a much longer time scale, 17 ps, by nonradiative decay. The electron-driven expansion is distinct from the phonon-driven dynamics observed along the radial direction, using the characteristic Bragg reflections; it occurs in 5 ps. These findings reveal the nonequilibrium distortion of the unit cell at early times and the role of the electron(phonon)-induced stress in the lattice dynamics of one-dimensional nanostructures.

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“…11 We adopted a LDA exchange-correlation functional in the Teter Pade parametrization, 12 and a norm-conserving…”

Section: S3 Ab Initio Calculationsmentioning

confidence: 99%

Origin of Axial and Radial Expansions in Carbon Nanotubes Revealed by Ultrafast Diffraction and Spectroscopy

2015

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“…In the field of quantum chemistry, there is a multitude of free density-functional theory [1,2] (DFT) codes using a wide variety of approaches to represent the molecular orbitals (MOs), such as plane-waves (e.g., ABINIT, [3,4] NWChem, [5,6] and Quantum ESPRESSO [7,8] ), wavelets (BigDFT, [9,10] DFT++ [11,12] and M-A-D-N-E-S-S [13] ), numerical atomic orbitals (OpenMX [14] and GPAW [15,16] ), and numerical grids (GPAW and Octopus [17,18] ), for example. However, these approaches (with the exception of multiresolution grids) become computationally problematic when hybrid DFT functionals [19] are used, due to the need to compute the exact exchange (see Hartree-Fock section).…”

Section: Introductionmentioning

confidence: 99%

ERKALE—A flexible program package for X‐ray properties of atoms and molecules

et al. 2012

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ERKALE is a novel software program for computing X-ray properties, such as ground-state electron momentum densities, Compton profiles, and core and valence electron excitation spectra of atoms and molecules. The program operates at Hartree-Fock or density-functional level of theory and supports Gaussian basis sets of arbitrary angular momentum and a wide variety of exchange-correlation functionals. ERKALE includes modern convergence accelerators such as Broyden and ADIIS and it is suitable for general use, as calculations with thousands of basis functions can routinely be performed on desktop computers. Furthermore, ERKALE is written in an object oriented manner, making the code easy to understand and to extend to new properties while being ideal also for teaching purposes.

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“…We performed LDA plane-wave pseudopotential calculations using the ABINIT code 18 and B3LYP and TD-B3LYP calculations with Gaussian basis sets using the G98 package. 19 Plane-wave cutoffs of at least 32 a.u.…”

Section: Methodsmentioning

confidence: 99%

Comparison of quantum Monte Carlo with time-dependent and static density-functional theory calculations of diamondoid excitation energies and Stokes shifts

2011

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We compute the absorption and emission energies and hence Stokes shifts of small diamondoids as a function of size using different theoretical approaches, including density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations. The absorption spectra of these molecules are also investigated by time-dependent DFT and compared with experiment. We analyze the structural distortion and formation of a self-trapped exciton in the excited state, and we study the effects of these on the Stokes shift as a function of size. Compared to recent experiments, QMC overestimates the excitation energies by about 0.8(1) eV on average. Benefiting from a cancellation of errors, the optical gaps obtained in DFT calculations with the B3LYP functional are in better agreement with experiment. It is also shown that time-dependent B3LYP calculations can reproduce most of the features found in the experimental spectra. According to our calculations, the structures of diamondoids in the excited state show a distortion which is hardly noticeable compared to that found for methane. As the number of diamond cages is increased, the distortion mechanism abruptly changes character. We have shown that the Stokes shift is size dependent and decreases with the number of diamond cages. If we neglect orbital symmetry effects on the optical excitations, the rate of decrease in the Stokes shift is, on average, 0.1 eV per cage for small diamondoids.

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ABINIT: First-principles approach to material and nanosystem properties

Cited by 2,502 publications

References 151 publications

Origin of Axial and Radial Expansions in Carbon Nanotubes Revealed by Ultrafast Diffraction and Spectroscopy

Origin of Axial and Radial Expansions in Carbon Nanotubes Revealed by Ultrafast Diffraction and Spectroscopy

ERKALE—A flexible program package for X‐ray properties of atoms and molecules

Comparison of quantum Monte Carlo with time-dependent and static density-functional theory calculations of diamondoid excitation energies and Stokes shifts

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