14 research outputs found
Structural, Electronic, and Vibrational Properties of Amino-adamantane and Rimantadine Isomers
We performed a first principles total energy investigation on the structural,
electronic, and vibrational properties of adamantane molecules, functionalized
with amine and ethanamine groups. We computed the vibrational signatures of
amantadine and rimantadine isomers with the functional groups bonded to
different carbon sites. By comparing our results with recent infrared and Raman
spectroscopic data, we discuss the possible presence of different isomers in
experimental samples
Functionalized adamantane: fundamental building blocks for nanostructure self-assembly
We report first principles calculations on the electronic and structural
properties of chemically functionalized adamantane molecules, either in
isolated or crystalline forms. Boron and nitrogen functionalized molecules,
aza-, tetra-aza-, bora-, and tetra-bora-adamantane, were found to be very
stable in terms of energetics, consistent with available experimental data.
Additionally, a hypothetical molecular crystal in a zincblende structure,
involving the pair tetra-bora-adamantane and tetra-aza-adamantane, was
investigated. This molecular crystal presented a direct and large electronic
bandgap and a bulk modulus of 20 GPa. The viability of using those
functionalized molecules as fundamental building blocks for nanostructure
self-assembly is discussed
Electrical conductivity of MgSiO3 at high temperatures and pressures: implications for the Earth's mantle
The electrical conductivity of magnesium silicate MgSiO3 has been studied,
using the framework of the first-principles density functional theory and the
Boltzmann transport theory, under the thermodynamic conditions of the Earth's
lower mantle. We find that the conductivity of pristine MgSiO3 depends strongly
on the structural phase of the material, as well as on temperature and
pressure. The conductivity of the perovskite phase increases with increasing
pressure (depth of the lower mantle) up to 90 GPa, then decreases at higher
pressures due to a change in the material's band gap transition from direct to
indirect. Finally, the structural phase transition that MgSiO3 undergoes near
the bottom of the lower mantle, from perovskite to post-perovskite, causes an
increase in the conductivity of MgSiO3, which should contribute to the increase
in the electrical conductivity of the Earth's mantle under the thermodynamic
conditions of the Earth's D" layer.Comment: 16 pages, 4 figures, 2 table
Doped 2D diamond: properties and applications
In the present paper, we investigate the structural, thermodynamic, dynamic,
elastic, and electronic properties of doped 2D diamond CX (X = B or N)
nanosheets in both AAA and ABC stacking configurations, by
first-principles calculations. Those systems are composed of 3 diamond-like
graphene sheets, with an undoped graphene layer between two 50% doped ones. Our
results, based on the analysis of ab-initio molecular dynamics simulations,
phonon dispersion spectra, and Born's criteria for mechanical stability,
revealed that all four structures are stable. Additionally, their standard
enthalpy of formation values are similar to the one of pristine 2D diamond,
recently synthesized by compressing three graphene layers. The CX (X =
B or N) systems exhibit high elastic constant values and stiffness comparable
to the diamond. The CN nanosheets present wide indirect band gaps that
could be advantageous for applications similar to the ones of the hexagonal
boron nitride (h-BN), such as a substrate for high-mobility 2D devices. On the
other hand, the CB systems are semiconductors with direct band gaps, in
the 1.6 - 2.0 eV range, and small effective masses, which are characteristics
that may be favorable to high carrier mobility and optoelectronics
applications
Group-IV graphene- and graphane-like nanosheets
We performed a first principles investigation on the structural and
electronic properties of group-IV (C, SiC, Si, Ge, and Sn) graphene-like sheets
in flat and buckled configurations and the respective hydrogenated or
fluorinated graphane-like ones. The analysis on the energetics, associated with
the formation of those structures, showed that fluorinated graphane-like sheets
are very stable, and should be easily synthesized in laboratory. We also
studied the changes on the properties of the graphene-like sheets, as result of
hydrogenation or fluorination. The interatomic distances in those graphane-like
sheets are consistent with the respective crystalline ones, a property that may
facilitate integration of those sheets within three-dimensional nanodevices