Daniele Selli - Academia.edu (original) (raw)

Papers by Daniele Selli

By means of ab initio metadynamics runs we explored the lower-pressure region of the phase diagra... more By means of ab initio metadynamics runs we explored the lower-pressure region of the phase diagram of germanium. A monoclinic germanium phase with four-membered rings, less dense than diamond and compressible into \beta-tin phase (tI4) was found. A metallic bct-5 phase, mechanically stable down to room conditions appeared between diamond and tI4. mC16 is a narrow-gap semiconductor, while bct-5 is metallic and potentially still superconducting in the very low pressure range. This finding may help resolving outstanding experimental issues.

Acta Crystallographica Section A Foundations and Advances, 2014

Journal of Physics Condensed Matter

We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab i... more We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab initio density functional theory. To accommodate the lattice mismatch between graphene and diamond, the overlayer deforms into a wavy structure that binds strongly to the diamond substrate. The detached ridges of the wavy graphene overlayer behave electronically as free-standing polyacetylene chains with delocalized π electrons, separated by regions containing only sp(3) carbon atoms covalently bonded to the (111) diamond surface. We performed quantum transport calculations for different geometries of the system to study how the buckling of the graphene layer and the associated bonding to the diamond substrate affect the transport properties. The system displays high carrier mobility along the ridges and a wide transport gap in the direction normal to the ridges. These intriguing, strongly anisotropic transport properties qualify the hybrid graphene-diamond system as a viable candidate fo...

Scientific Reports, 2013

Group-IVa elements silicon and germanium are known for their semiconducting properties at room te... more Group-IVa elements silicon and germanium are known for their semiconducting properties at room temperature, which are technologically critical. Metallicity and superconductivity are found at higher pressures only, Ge b-tin (tI4) being the first high-pressure metallic phase in the phase diagram. However, recent experiments suggest that metallicity in germanium is compatible with room conditions, calling for a rethinking of our understanding of its phase diagram. Missing structures can efficiently be identified based on structure prediction methods. By means of ab initio metadynamics runs we explored the lower-pressure region of the phase diagram of germanium. A monoclinic germanium phase (mC16) with four-membered rings, less dense than diamond and compressible into b-tin phase (tI4) was found. Tetragonal bct-5 appeared between diamond and tI4. mC16 is a narrow-gap semiconductor, while bct-5 is metallic and potentially still superconducting in the very low pressure range. This finding may help resolving outstanding experimental issues.

ChemInform, 2014

ABSTRACT Review: discussion of crystal structure predictions of novel carbon polymorphs with even... more ABSTRACT Review: discussion of crystal structure predictions of novel carbon polymorphs with even and odd rings; 47 refs.

Zeitschrift für anorganische und allgemeine Chemie, 2014

Carbon is a surprising material in all respects. In this Review, we present results of metadynami... more Carbon is a surprising material in all respects. In this Review, we present results of metadynamics calculations for crystal structure prediction of novel carbon polymorphs with even and odd rings. So-called superhard graphite results from cold-compressing graphite. We review the results of molecular dynamics simulations on the graphite-to-diamond phase transition, that yields Oganov's M-carbon. The Novel Carbons: Habits and Oddities Figure 7. Intermediate regime of TPS trajectory evolution. Snapshots are taken at the indicated times /ps. Cubic diamond is formed at first. In the insets of hexagonal diamond (Ͼ3 ps), 5,7 defects start forming (5-6 ps).

Zeitschrift für anorganische und allgemeine Chemie, 2012

The Journal of Physical Chemistry C, 2009

Finite-length models of chiral semiconducting carbon nanotubes based on Clar sextet theory allowe... more Finite-length models of chiral semiconducting carbon nanotubes based on Clar sextet theory allowed carrying out accurate calculations, performed by application of gradient-corrected density functional theory, on the energetic of sidewall reactions. In particular, we analyzed the addition of atomic fluorine and carbene (CH 2 ) to (6,4) and (6,5) nanotubes, finding excellent convergence of reaction energies with respect to the model length and good agreement with literature data. Our study demonstrates the importance of using models of carbon nanotubes based on chemical considerations to evaluate consistently the electronic and reactive properties of the sidewall.

Physical Review Letters, 2013

We use ab initio density functional calculations to determine the interaction of a graphene monol... more We use ab initio density functional calculations to determine the interaction of a graphene monolayer with the Si(111) surface. We found that graphene forms strong bonds to the bare substrate and accommodates the 12% lattice mismatch by forming a wavy structure consisting of free-standing conductive ridges that are connected by ribbon-shaped regions of graphene, which bond covalently to the substrate. We perform quantum transport calculations for different geometries to study changes in the transport properties of graphene introduced by the wavy structure and bonding to the Si substrate. Our results suggest that wavy graphene combines high mobility along the ridges with efficient carrier injection into Si in the contact regions.

$Research paper thumbnail of Superhard sp^{3} carbon allotropes with odd and even ring topologies$

Physical Review B, 2011

Four novel sp 3 -carbon allotropes with 6, 8 and 16 atoms per primitive cell have been derived us... more Four novel sp 3 -carbon allotropes with 6, 8 and 16 atoms per primitive cell have been derived using a combination of metadynamics simulations and topological scan. A novel chiral orthorhombic phase oC16 (C2221) was found to be harder than monoclinic M-carbon and shows remarkable stability in the high pressure range. A second orthorhombic phase of Cmmm symmetry, by ∼0.028 eV/atom energetically lower than W-Carbon, can be formed from graphite at ∼9GPa. In general, the mechanical response under pressure was found to depend on the structure topology, which reflects the way rings are formed from an initial graphene layer stacking.

Nanoscale, 2012

The possibility of tuning the electronic properties of graphene by tailoring the morphology at th... more The possibility of tuning the electronic properties of graphene by tailoring the morphology at the nanoscale or by chemical functionalization opens interesting perspectives towards the realization of devices for nanoelectronics. Indeed, the integration of the intrinsic high carrier mobilities of graphene with functionalities that are able to react to external stimuli allows in principle the realization of highly efficient nanostructured switches. In this paper, we report a novel approach to the design of reversible switches based on functionalized graphene nanoribbons, operating upon application of an external redox potential, which exhibit unprecedented ON/OFF ratios. The properties of the proposed systems are investigated by electronic structure and transport calculations based on density functional theory and rationalized in terms of valence-bond theory and Clar&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s sextet theory.

Journal of Physics: Condensed Matter, 2013

Nanoscale, 2016

Thermoelectric materials are strategically valuable for sustainable development, as they allow fo... more Thermoelectric materials are strategically valuable for sustainable development, as they allow for the generation of electrical energy from wasted heat. In recent years several strategies have demonstrated some efficiency in improving thermoelectric properties. Dopants affect carrier concentration, while thermal conductivity can be influenced by alloying and nanostructuring. Features at the nanoscale positively contribute to scattering phonons, however those with long mean free paths remain difficult to alter. Here we use the concept of hierarchical nano-grains to demonstrate thermal conductivity reduction in rocksalt lead chalcogenides. We demonstrate that grains can be obtained by taking advantage of the reconstructions along the phase transition path that connects the rocksalt structure to its high-pressure form. Since grain features naturally change as a function of size, they impact thermal conductivity over different length scales. To understand this effect we use a combination of advanced molecular dynamics techniques to engineer grains and to evaluate thermal conductivity in PbSe. By affecting grain morphologies only, i.e. at constant chemistry, two distinct effects emerge: the lattice thermal conductivity is significantly lowered with respect to the perfect crystal, and its temperature dependence is markedly suppressed. This is due to an increased scattering of low-frequency phonons by grain boundaries over different size scales. Along this line we propose a viable process to produce hierarchical thermoelectric materials by applying pressure via a mechanical load or a shockwave as a novel paradigm for material design.