24 research outputs found
Combining quantum and classical density functional theory for ion-electron mixtures
We combine techniques from quantum and from classical density functional
theory (DFT) to describe electron-ion mixtures. For homogeneous systems, we
show how to calculate ion-ion and ion-electron correlation functions within
Chihara's quantum hypernetted chain approximation, which we derive within a DFT
formulation. We also sketch out how to apply the DFT formulation to
inhomogeneous electron-ion mixtures, and use this to study the electron
distribution at the liquid-solid interface of Al.Comment: to be published in J. Non-Cryst. Solids, LAM 11 special issu
Probing Ion-Ion and Electron-Ion Correlations in Liquid Metals within the Quantum Hypernetted Chain Approximation
We use the Quantum Hypernetted Chain Approximation (QHNC) to calculate the
ion-ion and electron-ion correlations for liquid metallic Li, Be, Na, Mg, Al,
K, Ca, and Ga. We discuss trends in electron-ion structure factors and radial
distribution functions, and also calculate the free-atom and metallic-atom
form-factors, focusing on how bonding effects affect the interpretation of
X-ray scattering experiments, especially experimental measurements of the
ion-ion structure factor in the liquid metallic phase.Comment: RevTeX, 19 pages, 7 figure
Dynamical properties of liquid Al near melting. An orbital-free molecular dynamics study
The static and dynamic structure of liquid Al is studied using the orbital
free ab-initio molecular dynamics method. Two thermodynamic states along the
coexistence line are considered, namely T = 943 K and 1323 K for which X-ray
and neutron scattering data are available. A new kinetic energy functional,
which fulfills a number of physically relevant conditions is employed, along
with a local first principles pseudopotential. In addition to a comparison with
experiment, we also compare our ab-initio results with those obtained from
conventional molecular dynamics simulations using effective interionic pair
potentials derived from second order pseudopotential perturbation theory.Comment: 15 pages, 12 figures, 2 tables, submitted to PR
Ruthenium(II) dichloro or dithiocyanato complexes with 4,4′:2′,2″:4″,4‴-quaterpyridinium ligands:Towards photosensitisers with enhanced low-energy absorption properties
Fourteen new complexes of the form cis-\[RuIIX2(R2qpy2+)2]4+ (R2qpy2+ = a 4,4′:2′,2″:4″,4‴-quaterpyridinium ligand, X = Cl− or NCS−) have been prepared and isolated as their PF6− salts. Characterisation involved various techniques including 1H NMR spectroscopy and +electrospray or MALDI mass spectrometry. The UV–Vis spectra display intense intraligand π → π∗ absorptions, and also metal-to-ligand charge-transfer (MLCT) bands with two resolved maxima in the visible region. Red-shifts in the MLCT bands occur as the electron-withdrawing strength of the pyridinium groups increases, while replacing Cl− with NCS− causes blue-shifts. Cyclic voltammograms show quasi-reversible or reversible RuIII/II oxidation waves, and several ligand-based reductions that are irreversible. The variations in the redox potentials correlate with changes in the MLCT energies. A single-crystal X-ray structure has been obtained for a protonated form of a proligand salt, \[(4-(CO2H)Ph)2qpyH3+]\[HSO4]3·3H2O. Time-dependent density functional theory calculations give adequate correlations with the experimental UV–Vis spectra for the two carboxylic acid-functionalised complexes in DMSO. Despite their attractive electronic absorption spectra, these dyes are relatively inefficient photosensitisers on electrodes coated with TiO2 or ZnO. These observations are attributed primarily to weak electronic coupling with the surfaces, since the DFT-derived LUMOs include no electron density near the carboxylic acid anchors
Interpretation of diffusion coefficients in nanostructured materials from random walk numerical simulation
We make use of the numerical simulation random walk (RWNS) method to compute the ‘‘jump’’
diffusion coefficient of electrons in nanostructured materials via mean-square displacement. First,
a summary of analytical results is given that relates the diffusion coefficient obtained from RWNS
to those in the multiple-trapping (MT) and hopping models. Simulations are performed in a
three-dimensional lattice of trap sites with energies distributed according to an exponential
distribution and with a step-function distribution centered at the Fermi level. It is observed that
once the stationary state is reached, the ensemble of particles follow Fermi–Dirac statistics with a
well-defined Fermi level. In this stationary situation the diffusion coefficient obeys the theoretical
predictions so that RWNS effectively reproduces the MT model. Mobilities can be also computed
when an electrical bias is applied and they are observed to comply with the Einstein relation when
compared with steady-state diffusion coefficients. The evolution of the system towards the
stationary situation is also studied. When the diffusion coefficients are monitored along simulation
time a transition from anomalous to trap-limited transport is observed. The nature of this
transition is discussed in terms of the evolution of electron distribution and the Fermi level. All
these results will facilitate the use of RW simulation and related methods to interpret steady-state
as well as transient experimental technique
Structure of liquids composed of shifted dipole linear molecules
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