229 research outputs found
The two-dimensional Anderson model of localization with random hopping
We examine the localization properties of the 2D Anderson Hamiltonian with
off-diagonal disorder. Investigating the behavior of the participation numbers
of eigenstates as well as studying their multifractal properties, we find
states in the center of the band which show critical behavior up to the system
size considered. This result is confirmed by an independent
analysis of the localization lengths in quasi-1D strips with the help of the
transfer-matrix method. Adding a very small additional onsite potential
disorder, the critical states become localized.Comment: 26 RevTeX 3.0 pages with 13 figures included via psfi
Solvatochromic probe in molecular solvents : implicit versus explicit solvent model
Solvent-induced shifts in the absorption
spectrum of
N,N
-diethyl-4-nitroaniline were studied by
quantum-chemical methods in water, dimethylsulfoxide,
acetonitrile and acetone. TDDFT methodology and sem
iempirical ZINDO/S and PM6-CIS approaches were used
to calculate excitation energies. Solvent effect was mod
eled in implicit solvent model by different variants of the
PCM approach. Classical molecular dynamics was applied
to obtain solute-solvent geometries used in explicit solvent
modeling. Most implicit solvent models fail to reproduce
the sequence of solvatochromic shifts for four studied solvents, usually yielding too small effect for water. The best
result of the PCM method was obtained with SMD atomic
radii. Semiempirical quantum-chemical methods in explicit
solvent model did not provide satisfactory description of
solvatochromic shifts with the largest disagreement to
experiment observed for water. TDDFT explicit solvent
calculations performed the best in modeling of spectral
shifts. Problems with reproduction of experimental data
were attributed to specific interactions
Exponents of the localization lengths in the bipartite Anderson model with off-diagonal disorder
We investigate the scaling properties of the two-dimensional (2D) Anderson
model of localization with purely off-diagonal disorder (random hopping). In
particular, we show that for small energies the infinite-size localization
lengths as computed from transfer-matrix methods together with finite-size
scaling diverge with a power-law behavior. The corresponding exponents seem to
depend on the strength and the type of disorder chosen.Comment: 6 pages, 8 EPS-figures, requires phbauth.cl
TDDFT study of absorption spectrum of ketocyanine dye complexes with metal ions : explicit solvent model
Transition energies for a ketocyanine dye and its complexes with Li+ and Mg2+ ions with an implicit solvent have been studied. Molecular Dynamics simulations have been used to prepare structures of the dye in acetonitrle solution of lithium or magnesium perchlorate. TDDFT methodology has been used to calculate the transition energies for dye and dye-ion complexes solvated by an increasing number of acetonitrile molecules. Results have been compared to the predictions of the continuous solvation model. Evolution of the spectrum with the number of explicit solvent molecules has been observed and the solvent-induced shifts have been determined. It has been found that the explicit solvation model may predict sequence of transitions and their parentage different than that resulting from implicit solvation. Effect of the perchlorate counterion for the dye-cation spectrum has been also analyzed
Stabilization energies in charged tetracene clusters : quantum chemical and microelectrostatic calculations
Theoretical calculations of the stabilization energy for an excess electron in tetracene clusters are
presented. Vertical detachment energies were calculated for small clusters (up to 7 tetracene molecules)
using the quantum-chemical DFT method. For larger clusters and an infinite 2D layer of tetracene molecules, the self-consistent polarization field (SCPF) method was used to calculate the polarization energy
for a tetracene anion. Both DFT and SCPF results show that the charge stabilization energy increases
rapidly with the cluster size and, even for clusters of less than 10 tetracene molecules, amounts to more
than 50% of the bulk crystal value, which is in agreement with the conclusions of a recent experimental
work
Two interacting particles at the metal-insulator transition
To investigate the influence of electronic interaction on the metal-insulator
transition (MIT), we consider the Aubry-Andr\'{e} (or Harper) model which
describes a quasiperiodic one-dimensional quantum system of non-interacting
electrons and exhibits an MIT. For a two-particle system, we study the effect
of a Hubbard interaction on the transition by means of the transfer-matrix
method and finite-size scaling. In agreement with previous studies we find that
the interaction localizes some states in the otherwise metallic phase of the
system. Nevertheless, the MIT remains unaffected by the interaction. For a
long-range interaction, many more states become localized for sufficiently
large interaction strength and the MIT appears to shift towards smaller
quasiperiodic potential strength.Comment: 26 RevTeX 3.0 pages with 10 EPS-figures include
Exponents of the localization length in the 2D Anderson model with off-diagonal disorder
We study Anderson localization in two-dimensional systems with purely
off-diagonal disorder. Localization lengths are computed by the transfer-matrix
method and their finite-size and scaling properties are investigated. We find
various numerically challenging differences to the usual problems with diagonal
disorder. In particular, the divergence of the localization lengths close to
the band centre is investigated in detail for bipartite and non-bipartite
lattices as well as different distributions of the off-diagonal disorder.
Divergence exponents for the localization lengths are constructed that appear
to describe the data well down to at least 10^-5. We find only little evidence
for a crossover energy scale below which the power law has been argued to fail.Comment: 10 pages, 9 figures, uses PSS style files (included), submitted to
phys. stat. sol. (b
NaFSI and NaTFSI solutions in ether solvents from monoglyme to poly(ethylene oxide) : a molecular dynamics study
[Image: see text] Classical molecular dynamics simulations have been performed for a series of electrolytes based on sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide salts and monoglyme, tetraglyme, and poly(ethylene oxide) as solvents. Structural properties have been assessed through the analysis of coordination numbers and binding patterns. Residence times for Na–O interactions have been used to investigate the stability of solvation shells. Diffusion coefficients of ions and electrical conductivity of the electrolytes have been estimated from molecular dynamics trajectories. Contributions to the total conductivity have been analyzed in order to investigate the role of ion–ion correlations. It has been found that the anion–cation interactions are more probable in the systems with NaTFSI salts. Accordingly, the degree of correlations between ion motions is larger in NaTFSI-based electrolytes
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