3,416 research outputs found
First-principles calculation on the transport properties of molecular wires between Au clusters under equilibrium
Based on the matrix Green's function method combined with hybrid
tight-binding / density functional theory, we calculate the conductances of a
series of gold-dithiol molecule-gold junctions including benzenedithiol (BDT),
benzenedimethanethiol (BDMT), hexanedithiol (HDT), octanedithiol (ODT) and
decanedithiol (DDT). An atomically-contacted extended molecule model is used in
our calculation. As an important procedure, we determine the position of the
Fermi level by the energy reference according to the results from ultraviolet
photoelectron spectroscopy (UPS) experiments. After considering the
experimental uncertainty in UPS measurement, the calculated results of
molecular conductances near the Fermi level qualitatively agree with the
experimental values measured by Tao et. al. [{\it Science} 301, 1221 (2003);
{\it J. Am. Chem. Soc.} 125, 16164 (2003); {\it Nano. Lett.} 4, 267 (2004).]Comment: 12 pages,8 figure
Mempelajari Senyawa Mirisitrin Dengan Penambahan Substituen NH2, NO2, dan CH3 Sebagai Inhibitor Korosi Menggunakan Metode Density Fuctional Theory (DFT)
Corrosion inhibition ability myricitrin compound (M1) with the addition of NH2 (M2), NO2 (M3), and CH3 (M4) on the metal surface has been studied using Fuctional Density Theory (DFT) with a base set of B3LYP / 6-31G (d, p). Parameters obtained from the optimization result are the value EHOMO, ELUMO and dipole moment. Of the value EHOMO and ELUMO obtained and calculated the value of the energy gap (AE), ionization potential (IP), electron affinity (EA), electronegativity (χ), hardness (η), softness (σ), electron transfer (ΔN), and electrophilicity (ω). Computational calculations show that the compound M4 has the best corrosion inhibition ability. Based on the value EHOMO, the energy gap (AE), ionization potential (IP), hardness (η), softness (σ) and electron transfer (ΔN).
Keywords: DFT, Corrosion Inhibition, EHOMO, ELUM
Size dependent electronic properties of silicon quantum dots - an analysis with hybrid, screened hybrid and local density functional theory
We use an efficient projection scheme for the Fock operator to analyze the
size dependence of silicon quantum dots (QDs) electronic properties. We compare
the behavior of hybrid, screened hybrid and local density functionals as a
function of the dot size up to 800 silicon atoms and volume of up to
20nm. This allows comparing the calculations of hybrid and screened
hybrid functionals to experimental results over a wide range of QD sizes. We
demonstrate the size dependent behavior of the band gap, density of states,
ionization potential and HOMO level shift after ionization. Those results are
compared to experiment and to other theoretical approaches, such as
tight-binding, empirical pseudopotentials, TDDFT and GW
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A low-bandgap dimeric porphyrin molecule for 10% efficiency solar cells with small photon energy loss
Dimeric porphyrin molecules have great potential as donor materials for high performance bulk heterojunction organic solar cells (OSCs). Recently reported dimeric porphyrins bridged by ethynylenes showed power conversion efficiencies (PCEs) of more than 8%. In this study, we design and synthesize a new conjugated dimeric D-A porphyrin ZnP2BT-RH, in which the two porphyrin units are linked by an electron accepting benzothiadiazole (BT) unit. The introduction of the BT unit enhances the electron delocalization, resulting in a lower highest occupied molecular orbital (HOMO) energy level and an increased molar extinction coefficient in the near-infrared (NIR) region. The bulk heterojunction solar cells with ZnP2BT-RH as the donor material exhibit a high PCE of up to 10% with a low energy loss (Eloss) of only 0.56 eV. The 10% PCE is the highest for porphyrin-based OSCs with a conventional structure, and this Eloss is also the smallest among those reported for small molecule-based OSCs with a PCE higher than 10% to date
Photochromic Switching and Fine-Tuning of the Hole-Injection in Solution-Processed Organic Light-Emitting Devices
BN Nanotube Serving as a Gas Chemical Sensor for N₂O by Parallel Electric Field
Density functional theory calculations were performed to understand the electronic properties of C₂₄, B₁₂N₁₂, B₁₂P₁₂, and (6, 0) BNNT interacted with N₂O molecule in the presence and absence of an external electric field using the B3LYP method and 6-31G** basis set. The adsorption of N₂O from O-side on the surface of (6, 0) BNNT has high sensitivity in comparison with B₁₂N₁₂ nano-cage. The adsorption energy of N₂O (O-side) on the sidewalls of B₁₂N₁₂ and BNNT in the presence of an electric field are −21.01 and −15.48 kJ mol⁻¹, respectively. Our results suggest that in the presence of an electric field, the B₁₂N₁₂ nano-cage is the more energetically notable upon the N₂O adsorption than (6, 0) BNNT, C₂₄, and B₁₂P₁₂. Whereas, our results indicate that the electronic property of BNNT is more sensitive to N₂O molecule at the presence of an electric field than B₁₂N₁₂ nano-cage. It is anticipated that BNNT could be a favorable gas sensor for the detection of N₂O molecule. © 2016, Springer Science+Business Media New York
Electronic Structure Shift of Deep Nanoscale Silicon by SiO- vs. SiN-Embedding as Alternative to Impurity Doping
Conventional impurity doping of deep nanoscale silicon (dns-Si) used in ultra
large scale integration (ULSI) faces serious challenges below the 14 nm
technology node. We report on a new fundamental effect in theory and
experiment, namely the electronic structure of dns-Si experiencing energy
offsets of ca. 1 eV as a function of SiO- vs. SiN-embedding with a
few monolayers (MLs). An interface charge transfer (ICT) from dns-Si specific
to the anion type of the dielectric is at the core of this effect and arguably
nested in quantum-chemical properties of oxygen (O) and nitrogen (N) vs. Si. We
investigate the size up to which this energy offset defines the electronic
structure of dns-Si by density functional theory (DFT), considering interface
orientation, embedding layer thickness, and approximants featuring two Si
nanocrystals (NCs); one embedded in SiO and the other in SiN.
Working with synchrotron ultraviolet photoelectron spectroscopy (UPS), we use
SiO- vs. SiN-embedded Si nanowells (NWells) to obtain their energy
of the top valence band states. These results confirm our theoretical findings
and gauge an analytic model for projecting maximum dns-Si sizes for NCs,
nanowires (NWires) and NWells where the energy offset reaches full scale,
yielding to a clear preference for electrons or holes as majority carriers in
dns-Si. Our findings can replace impurity doping for n/p-type dns-Si as used in
ultra-low power electronics and ULSI, eliminating dopant-related issues such as
inelastic carrier scattering, thermal ionization, clustering, out-diffusion and
defect generation. As far as majority carrier preference is concerned, the
elimination of those issues effectively shifts the lower size limit of Si-based
ULSI devices to the crystalization limit of Si of ca. 1.5 nm and enables them
to work also under cryogenic conditions.Comment: 14 pages, 17 Figures with a total 44 graph
Simulating the nanomechanical response of cyclooctatetraene molecules on a graphene device
We investigate the atomic and electronic structures of cyclooctatetraene
(COT) molecules on graphene and analyze their dependence on external gate
voltage using first-principles calculations. The external gate voltage is
simulated by adding or removing electrons using density functional theory (DFT)
calculations. This allows us to investigate how changes in carrier density
modify the molecular shape, orientation, adsorption site, diffusion barrier,
and diffusion path. For increased hole doping COT molecules gradually change
their shape to a more flattened conformation and the distance between the
molecules and graphene increases while the diffusion barrier drastically
decreases. For increased electron doping an abrupt transition to a planar
conformation at a carrier density of -810 e/cm is observed.
These calculations imply that the shape and mobility of adsorbed COT molecules
can be controlled by externally gating graphene devices
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