Claudia Cardoso

Computational study of molecules with high intrinsic hyperpolarizabilities.

In the current manuscript we present the results of a computational study on a series of chromophores with enhanced intrinsic hyperpolarizability. The high hyperpolarizability values of these molecules were previously reported and were achieved by making use of aromatic moieties in order to modulate the aromatic stabilization energy along the conjugated bridge between the donor and the acceptor. Calculations were performed using semiempirical, DFT, and TDDFT methods, and the results reproduce the trend determined experimentally for the first hyperpolarizability values. Several calculation schemes were used, and the best agreement was achieved when long-range Hartree-Fock exchange corrections and solvent effects are included in the DFT calculations. The long-range corrections proved to be especially important for the azobenzene derivatives, which otherwise have their hyperpolarizability overestimated considerably in the DFT calculations. The results are also analyzed within the framework of a two-level model, which correctly reproduces the trend in the hyperpolarizabilities of the molecules under study.

Structure Dependence of Hyperpolarizability in Octopolar Molecules.

Recent Hyper Rayleigh Scattering measurements report a significant increase of second-order hyperpolarizability upon introduction of positive charges at the pyridyl end groups in trispyridyl octopolar chromophores. We calculated the geometries, linear response, and first-order hyperpolarizabilities of a series of six trispyridyl molecules both in the neutral and protonated forms. The calculations were performed with ab initio and semiempirical methods. The results are in good agreement with the experimental values and a correlation between the first hyperpolarizability and two structural properties, the N-C bond elongation and the C-C bond length alternation, ⟨Δr⟩ was established. To test these effects we computed the hyperpolarizability for several constrained geometries and confirmed the importance of planarity on the hyperpolarizability values. However the ⟨Δr⟩ values alone seem to have little influence both on the hyperpolarizability and on the gap values. Replacing the triple C≡C bond by a double C=C bond in the conjugation bridge has no significant effect due to the strong hyperpolarizability dependence on the pyridyl-benzene dihedral angle.

Ab-initio calculations of the Ruddlesden?Popper phases CaMnO3, CaO(CaMnO3) and CaO(CaMnO3)2

The present work reports ab-initio density functional theory calculations for the Ruddlesden–Popper phase CaO(CaMnO3)n compounds. In order to study the evolution of the properties with the number of perovskite layers, a detailed analysis of the densities of states calculated for each compound and for several magnetic configurations was performed. The effect of distortions of the crystal structure on the magnetic ground state is also analysed and the exchange constants and transition temperatures are calculated for the three compounds using a mean field model. The calculated magnetic ground state structures and magnetic moments are in good agreement with experimental results and previous calculations.

Marine natural products from the deep Pacific as potential non-linear optical chromophores

Theoretical analysis using quadratic response theory within the time-dependent density functional theory (TDDFT) formalism shows that the dermacozines, a group of phenazine-based compounds isolated from cultures of Dermacoccus abyssi found in the Mariana Trench, possess large first hyperpolarisability (β) values at common incident laser wavelengths that are highly sensitive to the degree and type of substitution of the core structure. The phenazine moiety is a versatile and tunable chromophore for non-linear optics and this work serves to highlight the potential that (marine) natural products, even those found in the darkest places on the planet, may have for aiding developments in optical materials design.

FePc Adsorption on the Moire Superstructure of Graphene Intercalated with a Cobalt Layer

The moire superstructure of graphene grown on metals can drive the assembly of molecular architectures, such as iron–phthalocyanine (FePc) molecules, allowing for the production of artificial molecular configurations. A detailed analysis of the Gr/Co interaction upon intercalation (including a modeling of the resulting moire pattern) is performed here by density functional theory, which provides an accurate description of the template as a function of the corrugation parameters. The theoretical results are a preliminary step to describe the interaction process of the FePc molecules adsorption on the Gr/Co system. Core level photoemission and absorption spectroscopies have been employed to control the preferential adsorption regions of the FePc on the graphene moire superstructure and the interaction of the central Fe ion with the underlying Co. Our results show that, upon molecular adsorption, the distance of C atoms from the Co template mainly drives the strength of the molecules-substrate interaction, t...

Electronic Structure Evolution during the Growth of Graphene Nanoribbons on Au(110)

Surface-assisted polymerization of molecular monomers into extended chains can be used as the seed of graphene nanoribbon (GNR) formation, resulting from a subsequent cyclo-dehydrogenation process. By means of valence-band photoemission and ab initio density-functional theory (DFT) calculations, we investigate the evolution of molecular states from monomer 10,10′-dibromo-9,9′bianthracene (DBBA) precursors to polyanthryl polymers, and eventually to GNRs, as driven by the Au(110) surface. The molecular orbitals and the energy level alignment at the metal–organic interface are studied in depth for the DBBA precursors deposited at room temperature. On this basis, we identify a spectral fingerprint of C–Au interaction in both DBBA single-layer and polymerized chains obtained upon heating. Furthermore, DFT calculations help us by evidencing that GNRs interact more strongly than DBBA and polyanthryl with the Au(110) substrate, as a result of their flatter conformation.

A study of the magnetic structure of YFe4Al8

A study of the magnetic structure of YFe4Al8 is presented, based on the reported magnetic structure, as given by a neutron diffraction study; cycloid, with moments in the a–b plane and with two Fe sublattices with a 140° phase difference between them. Calculations were performed, using density functional theory, for cycloids with , with τ varying between 0 and 1. The calculated magnetic structure agrees with the structure deduced from neutron diffraction results, however with a simpler description. The YFe4Al8 magnetic structure can be described by a single Fe lattice with a cycloid propagation vector with τ = 0.865; there is no need for a second Fe lattice with an arbitrary phase difference. We show that the same description can be applied to DyFe4Al8 and HoFe4Al8.

Magnetism of the series UFexAl12−x

Abstract Recent results from low-temperature specific heat and magnetization measurements performed on crystals of UFe x Al 12− x (3.8 x

Evolution of magnetism in the UFexAl12−x intermetallic series

Single crystals of UFexAl12−x for 4<x<5 were studied by magnetization and specific heat measurements. Based on these results, the evolution of magnetism in this series is discussed.

2,2,6,6-Tetramethyl-4-oxopiperidinium nitrate.

In the title compound, C(9)H(18)NO(+).NO(3)(-), the piperidinium ring adopts a slightly deformed chair conformation and the nitrate anion is disordered. The ions are arranged in hydrogen-bonded chains parallel to [001], in which the cations alternate with the anions. The intrachain hydrogen bonds are bifurcated and link the O atoms of the anions to the N atoms of the cations.