arXiv subjects

Daniel Sánchez-Portal

Publications and source records attributed to Daniel Sánchez-Portal.

21 records · Page 2Linked to original sources

arXiv2011

Strain-Tunable Spin Moment in Ni-Doped Graphene

Graphene, due to its exceptional properties, is a promising material for nanotechnology applications. In this context, the ability to tune the properties of graphene-based materials and devices with the incorporation of defects and impurities can be of extraordinary importance. Here we investigate the effect of uniaxial tensile strain on the electronic and magnetic properties of graphene doped with substitutional Ni impurities (Ni_sub). We have found that, although Ni_sub defects are non-magnetic in the relaxed layer, uniaxial strain induces a spin moment in the system. The spin moment increases with the applied strain up to values of 0.3-0.4 μ_B per Ni_sub, until a critical strain of ~6.5% is reached. At this point, a sharp transition to a high-spin state (~1.9 μ_B) is observed. This magnetoelastic effect could be utilized to design strain-tunable spin devices based on Ni-doped graphene.

cond-mat.mes-hall↗

arXiv2011

An O(N^3) implementation of Hedin's GW approximation for molecules

We describe an implementation of Hedin's GW approximation for molecules and clusters, the complexity of which scales as O(N^3) with the number of atoms. Our method is guided by two strategies: i) to respect the locality of the underlying electronic interactions and ii) to avoid the singularities of Green's functions by manipulating, instead, their spectral functions using FFT methods. To take into account the locality of the electronic interactions, we use a local basis of atomic orbitals and, also, a local basis in the space of their products. We further compress the screened Coulomb interaction into a space of lower dimensions for speed and to reduce memory requirements. The improved scaling of our method with respect to most of the published methodologies should facilitate GW calculations for large systems. Our implementation is intended as a step forward towards the goal of predicting, prior to their synthesis, the ionization energies and electron affinities of the large molecules that serve as constituents of organic semiconductors.

cond-mat.other↗

arXiv2010

First-principles investigation of electron-induced cross-linking of aromatic self-assembled monolayers on Au(111)

We have performed a density functional theory study of the possible layered geometries occurring after dehydrogenation of a self-assembled monolayer (SAM) of biphenyl-thiol molecules (BPTs) adsorbed on a Au(111), as it has been experimentally observed for low energy electron irradiated SAMs of 4'-nitro-1,1'-biphenyl-thiol adsorbed on a Au(111) surface. [Eck, W. et al., Advanced Materials 2000, 12, 805] Cross-link formation between the BPT molecules has been analyzed using different models with different degrees of complexity. We start by analyzing the bonding between biphenyl (BP) molecules in a lineal dimer and their characteristic vibration frequencies. Next, we consider the most stable cross-linked structures formed in an extended free-standing monolayer of fully dehydrogenated BP molecules. Finally, we analyze a more realistic model where the role of the Au(111) substrate and sulphur head groups is explicitly taken into account. In this more complex model, the dehydrogenated BPT molecules are found to interact covalently to spontaneously form "graphene-like" nanoflakes. We propose that these nanographenes provide plausible building-blocks for the structure of the carbon layers formed by electron irradiation of BPT-SAMs. In particular, it is quite tempting to visualize those structures as the result of the cross-link and entanglement of such graphene nanoflakes.

cond-mat.mes-hall↗