Charge transport pathways in metal porphyrin as interplay between long and short range scattering processes.

We have investigated the ballistic transport for Mn, Fe-porphyrin molecules in contact with Au(111) electrodes by using density functional theory. We show that the information resulted from the projected density of electronic states does not provide a complete picture of the transport mechanism. Instead, we propose a methodology based on the concept of the orbital projected transmissions for selected groups of atoms. We have found that the transmission channels for occupied states can be assigned to short range scattering processes at gold-molecule interface, while for the states above Fermi level the transmission takes place via long range scattering processes. The interplay between these two conduction mechanisms is responsible for the transport path in metal-porphyrin; our model is in qualitative agreement with the existing experimental data on transport pathway on single porphyrin molecules.

Translation of metal-phthalocyanines adsorbed on Au(111): from van der Waals interaction to strong electronic correlation.

Using first-principles calculations, we investigate the binding energy for six transition metal - phthalocyanine molecules adsorbed on Au(111). We focus on the effect of translation on molecule - surface physical properties; van der Waals interactions as well as the strong correlation in d orbitals of transition metals are taken into account in all calculations. We found that dispersion interaction and charge transfer have the dominant role in the molecule-surface interaction, while the interaction between the transition metal and gold has a rather indirect influence over the physics of the molecule-surface system. A detailed analysis of the physical properties of the adsorbates at different geometric configurations allows us to propose qualitative models to account for all values of interface dipole charge transfer and magnetic moment of metal-phthalocyanines adsorbed on Au(111).

Charge and spin transport in single and packed ruthenium-terpyridine molecular devices: Insight from first-principles calculations.

Using first-principles calculations, we study the electronic and transport properties of rutheniumterpyridine molecules sandwiched between two Au(111) electrodes. We analyse both single and packed molecular devices, more amenable to scaling and realistic integration approaches. The devices display all together robust negative differential resistance features at low bias voltages. Remarkably, the electrical control of the spin transport in the studied systems implies a subtle distribution of the magnetisation density within the biased devices and highlights the key role of the Au(111) electrical contacts.

Magnetism and electronic structure calculation of SmN.

The results of the electronic structure calculations performed on SmN by using the LDA+U method with and without including the spin-orbit coupling are presented. Within the LDA+U approach, a N(2p) band polarization of about 0.3 µB is induced by Sm(4f)-N(2p) hybridization, and a half-metallic ground state is obtained. By including spin-orbit coupling the magnetic structure was shown to be antiferromagnetic of type II, with Sm spin and orbital moments nearly cancelling. This results into a semiconducting ground state, which is in agreement with experimental results.

A study of the anharmonic effects on the vibrational spectra of a realistic retinal chromophore model.

Ab initio and vibrational self-consistent field (VSCF) computations are used to investigate the vibrational normal coordinates of the protonated Schiff base (PSB) 4-cis-gamma,eta-dimethyl-C9H9 NH2+. The ground and the first excited states are investigated. Both harmonic and anharmonic frequencies for the first three overtones of the ground and first excited states are reported. Special attention is payed to the discussion of the normal coordinates modes that involve the central C=C bond which plays a significant role in the isomerization process.

Vibrational properties of the free and adsorbed acridone.

Theoretical density functional theory (DFT) calculation, ab initio and experimental vibrational characterization of acridone were performed. The computed vibrational modes agree well with the experimental values of the related crystal structure. Surface enhanced Raman scattering (SERS) of acridone in silver colloids with different surface potential values was studied. FT-SERS spectrum of acridone revealed different adsorption behavior of the title compound on the silver particles.

Numerical simulations of Raman spectra of guanine-cytosine Watson-Crick and protonated Hoogsteen base pairs.

Large changes in the Raman spectra of calf thymus DNA are observed upon lowering the pH. In order to gain a better insight into these effects, several simulations of the Raman spectra of the guanine-cytosine (GC) Watson-Crick and Hoogsteen base pairs are performed. By comparing the Raman bands of GC base pairs in calf thymus DNA at high and low pH with the theoretical simulations of GC base pairs, it is found that the intensity changes in the theoretical bands located between 400 and 1000 cm(-1) are small compared to the experimental ones. The behavior of the cytosine band at 1257 cm(-1) upon lowering the pH is not reproduced in the GC theoretical spectra. The bands located above 1300 cm(-1) in the theoretical spectra display intensity changes that are similar to those found for GC base pairs in calf thymus DNA spectra.