1,500 research outputs found
Polymer adhesion: first-principles calculations of the adsorption of organic molecules onto Si surfaces
The structures and energetics of organic molecules adsorbed onto clean and
H-passivated Si(001)-(21) surfaces have been calculated using density
functional theory. For benzene adsorbed on the clean Si surface the
tight-bridge structure was found to be stable and the butterfly structure
metastable. Both carbonic acid HCO and propane CH dissociate on
contact with the surface. Passivation of the Si surface with H-atoms has a
dramatic effect on the surface properties. The passivated surface is very inert
and the binding energy of all the molecules is very weak.Comment: 8 pages, 13 figure
A hierarchical dualscale study of bisphenol-A-polycarbonate on a silicon surface : structure, dynamics and impurity diffusion
A previously developed and studied coarse-grained model is used to investigate the properties of bisphenol-A-polycarbonate (BPA-PC) in contact with the Si(001)-(2 x 1) surface. The surface interaction potentials are based on density functional calculations. Both a smooth wall potential and a site-dependent wall potential were used to represent the surface. For both types of surface potential it was found that only the chain ends adsorb and the density profiles and conformations in each case are similar. The site-dependent surface slows the dynamics of the polymer at the interface by an order of magnitude compared to the bulk dynamics for the chain lengths considered. The diffusion of non-adsorbing impurity particles for both surface potentials was investigated and the concentration and dynamics of the impurity particles were analysed
Quantized evolution of the plasmonic response in a stretched nanorod
Quantum aspects, such as electron tunneling between closely separated
metallic nanoparticles, are crucial for understanding the plasmonic response of
nanoscale systems. We explore quantum effects on the response of the
conductively coupled metallic nanoparticle dimer. This is realized by
stretching a nanorod, which leads to the formation of a narrowing atomic
contact between the two nanorod ends. Based on first-principles time-dependent
density-functional-theory calculations, we find a discontinuous evolution of
the plasmonic response as the nanorod is stretched. This is especially
pronounced for the intensity of the main charge-transfer plasmon mode. We show
the correlation between the observed discontinuities and the discrete nature of
the conduction channels supported by the formed atomic-sized junction.Comment: Main text: 6 pages, 2 figures; Supplemental Material: 5 pages, 4
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Comment on "Binding of hydrogen molecules by a transition-metal ion"
A Comment on the Letter by Niu, Rao, and Jena Phys. Rev. Lett. 68, 2277 (1992).Peer reviewe
Atomic-scale modeling of the ion-beam-induced growth of amorphous carbon
The results of a detailed molecular-dynamics study of the growth of amorphous carbon (a−C) are reported. Carbon atoms with kinetic energies between 10 and 150 eV are deposited on a−C surface originating from bulk a−C. Earlier simulation results of an optimal energy window at 40–70 eV are confirmed. Additionally, it is found that the growth rate is at maximum at around 40 eV. At low implantation energies (Ebeam≈10 eV), the growth of amorphous carbon takes place on the surface. At higher energies, the growth proceeds increasingly in the subsurface region by global film expansion and single atom diffusion towards the surface. Scattering events (e.g., the deposited atom does not adsorb to the surface) at intermediate energies Ebeam≈100 eV result in a densification of the growing film. Moreover, at Ebeam≈150 eV, nonpermanent diamond formation is observed.Peer reviewe
Nanoplasmonics simulations at the basis set limit through completeness-optimized, local numerical basis sets
We present an approach for generating local numerical basis sets of improving
accuracy for first-principles nanoplasmonics simulations within time-dependent
density functional theory. The method is demonstrated for copper, silver, and
gold nanoparticles that are of experimental interest but computationally
demanding due to the semi-core d-electrons that affect their plasmonic
response. The basis sets are constructed by augmenting numerical atomic orbital
basis sets by truncated Gaussian-type orbitals generated by the
completeness-optimization scheme, which is applied to the photoabsorption
spectra of homoatomic metal atom dimers. We obtain basis sets of improving
accuracy up to the complete basis set limit and demonstrate that the
performance of the basis sets transfers to simulations of larger nanoparticles
and nanoalloys as well as to calculations with various exchange-correlation
functionals. This work promotes the use of the local basis set approach of
controllable accuracy in first-principles nanoplasmonics simulations and
beyond.Comment: 11 pages, 6 figure
Fast convergence to equilibrium for long-chain polymer melts using a MD/continuum hybrid method
Effective and fast convergence toward an equilibrium state for long-chain
polymer melts is realized by a hybrid method coupling molecular dynamics and
the elastic continuum. The required simulation time to achieve the equilibrium
state is reduced drastically compared with conventional equilibration methods.
The polymers move on a wide range of the energy landscape due to large-scale
fluctuation generated by the elastic continuum. A variety of chain structures
is generated in the polymer melt which results in the fast convergence to the
equilibrium state.Comment: 13 page
Kohn-Sham decomposition in real-time time-dependent density-functional theory: An efficient tool for analyzing plasmonic excitations
The real-time-propagation formulation of time-dependent density-functional
theory (RT-TDDFT) is an efficient method for modeling the optical response of
molecules and nanoparticles. Compared to the widely adopted linear-response
TDDFT approaches based on, e.g., the Casida equations, RT-TDDFT appears,
however, lacking efficient analysis methods. This applies in particular to a
decomposition of the response in the basis of the underlying single-electron
states. In this work, we overcome this limitation by developing an analysis
method for obtaining the Kohn-Sham electron-hole decomposition in RT-TDDFT. We
demonstrate the equivalence between the developed method and the Casida
approach by a benchmark on small benzene derivatives. Then, we use the method
for analyzing the plasmonic response of icosahedral silver nanoparticles up to
Ag. Based on the analysis, we conclude that in small nanoparticles
individual single-electron transitions can split the plasmon into multiple
resonances due to strong single-electron-plasmon coupling whereas in larger
nanoparticles a distinct plasmon resonance is formed.Comment: 11 pages, 3 figure
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