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

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

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 $N= 200 \times 200$ 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

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

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

Hydrogen bonding and infrared spectra of ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/water mixtures : a view from molecular dynamics simulations

[Image: see text] Simulations of ab initio molecular dynamics have been performed for mixtures of ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) ionic liquid and water. Statistics of donors and acceptors of hydrogen bonds has revealed that with increasing water content, hydrogen bonds between EMIM cations and TFSI anions are replaced by bonds to water molecules. In the mixture of liquids, the total number of bonds (from EMIM cations or water molecules) formed by TFSI acceptors increases. IR spectra obtained from ab initio molecular dynamics trajectories are in good agreement with literature data for ionic liquid/water systems. Analysis of oscillations of individual C–H and O–H bonds has shown correlations between vibrational frequencies and hydrogen bonds formed by an EMIM cation or water molecule and has indicated that the changes in the IR spectrum result from the decreased number of water–water hydrogen bonds in the mixture. The tests of DFTB methodology with tailored parameterizations have yielded reasonably good description of the IR spectrum of bulk water, whereas available parameterizations have failed in satisfactory reproduction of the IR spectrum of EMIM-TFSI/water mixtures in the region above 3000 cm(–1)

Explicit and hybrid solvent models for estimates of parameters relevant to the reduction potential of ethylene carbonate

Using ethylene carbonate as a sample solvent, we investigated two molecular parameters used to estimate the reduction potential of the solvent: electron affinity, and the energy of the lowest unoccupied molecular orbital (LUMO). The results showed that the values of these parameters are inconsistent for a single ethylene carbonate molecule in vacuum calculations and in the continuous effective solvent. We performed a series of calculations employing explicit or hybrid (explicit/continuous) solvent models for aggregates of solvent molecules or solvated salt ions. In the hybrid solvent model, values of the two estimates extrapolated to an infinite system size converged to one common value, whereas the difference of 1 eV was calculated in the purely explicit solvent. The values of the gap between the highest occupied molecular orbital (HOMO) and the LUMO obtained in the hybrid model were significantly larger than those resulting from the explicit solvent calculations. We related these differences to the differences in frontier orbitals and changes of electron density obtained in the two solvent models. In the hybrid solvent model, the location of the additional electron in the reduced system usually corresponds to the LUMO orbital of the oxidized system. The presence of salt ions in the solvent affects the extrapolated values of the electron affinity and LUMO energy