12 research outputs found
Structure and properties of small sodium clusters
We have investigated structure and properties of small metal clusters using
all-electron ab initio theoretical methods based on the Hartree-Fock
approximation and density functional theory, perturbation theory and compared
results of our calculations with the available experimental data and the
results of other theoretical works. We have systematically calculated the
optimized geometries of neutral and singly charged sodium clusters having up to
20 atoms, their multipole moments (dipole and quadrupole), static
polarizabilities, binding energies per atom, ionization potentials and
frequencies of normal vibration modes. Our calculations demonstrate the great
role of many-electron correlations in the formation of electronic and ionic
structure of small metal clusters and form a good basis for further detailed
study of their dynamic properties, as well as structure and properties of other
atomic cluster systems.Comment: 47 pages, 16 figure
Electronic structure of the [Ni(Salen)] complex studied by core-level spectroscopies
The nature and structure of occupied and empty valence electronic states (molecular orbitals, MOs) of the [Ni(Salen)] molecular complex (NiO2N2C16H14) have been studied by X-ray photoemission and absorption spectroscopy combined with density functional theory (DFT) calculations. As a result, the composition of the high-lying occupied and low-lying unoccupied electronic states has been identified. In particular, the highest occupied molecular orbital (HOMO) of the complex is found to be predominantly located on the phenyl rings of the salen ligand, while the states associated with the occupied Ni 3d-derived molecular orbitals (MOs) are at higher binding energies. The lowest unoccupied molecular orbital (LUMO) is also located on the salen ligand and is formed by the 2pπ orbitals of carbon atoms in phenyl groups of the salen macrocycle. The unoccupied MOs above the LUMO reflect σ- and π-bonding between Ni and its nearest neighbours. All valence states have highly mixed character. The specific nature of the unoccupied Ni 3d-derived σ-MO is a consequence of donor-acceptor chemical bonding in [Ni(Salen)]. This journal i
Lithiation Products of a Silicon Anode Based on Soft X‑ray Emission Spectroscopy: A Theoretical Study
Because
of its exceptional lithium storage capacity, silicon is
considered as a promising candidate for anode material in lithium-ion
batteries (LIBs). In the present work, we demonstrate that methods
of soft X-ray emission spectroscopy can be used as a powerful tool
for the comprehensive analysis of the electronic and structural properties
of lithium silicides Li<i><sub>x</sub></i>Si forming in
LIB’s anode upon Si lithiation. On the basis of density functional
theory and molecular dynamics simulations, it is shown that the coordination
number of Si atoms in Li<i><sub>x</sub></i>Si decreases
with an increase in Li concentration both for the crystalline and
amorphous phases. In amorphous a-Li<i><sub>x</sub></i>Si
alloys, Si tends to cluster, forming Si–Si covalent bonds even
at the high lithium concentration. It is demonstrated that the Si-L<sub>2,3</sub> emission bands of the crystalline and amorphous Li<i><sub>x</sub></i>Si alloys show different spectral dependencies,
reflecting the process of disintegration of Si–Si network into
Si clusters and chains of the different sizes upon Si lithiation.
The Si-L<sub>2,3</sub> emission bands of Li<i><sub>x</sub></i>Si alloys become narrower and shift toward higher energies with an
increase in Li concentration. The shape of the emission band depends
on the relative contribution of the X-ray radiation from the Si atoms
having different coordination numbers. This feature of the Si-L<sub>2,3</sub> spectra of Li<i><sub>x</sub></i>Si alloys can
be used for the detailed analysis of the Si lithiation process and
LIB’s anode structure identification
From Graphene Nanoribbons on Cu(111) to Nanographene on Cu(110): Critical Role of Substrate Structure in the Bottom-Up Fabrication Strategy.
Bottom-up strategies can be effectively implemented for the fabrication of atomically precise graphene nanoribbons. Recently, using 10,10'-dibromo-9,9'-bianthracene (DBBA) as a molecular precursor to grow armchair nanoribbons on Au(111) and Cu(111), we have shown that substrate activity considerably affects the dynamics of ribbon formation, nonetheless without significant modifications in the growth mechanism. In this paper we compare the on-surface reaction pathways for DBBA molecules on Cu(111) and Cu(110). Evolution of both systems has been studied via a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and theoretical calculations. Experimental and theoretical results reveal a significant increase in reactivity for the open and anisotropic Cu(110) surface in comparison with the close-packed Cu(111). This increased reactivity results in a predominance of the molecular-substrate interaction over the intermolecular one, which has a critical impact on the transformations of DBBA on Cu(110). Unlike DBBA on Cu(111), the Ullmann coupling cannot be realized for DBBA/Cu(110) and the growth of nanoribbons via this mechanism is blocked. Instead, annealing of DBBA on Cu(110) at 250 °C results in the formation of a new structure: quasi-zero-dimensional flat nanographenes. Each nanographene unit has dehydrogenated zigzag edges bonded to the underlying Cu rows and oriented with the hydrogen-terminated armchair edge parallel to the [1-10] direction. Strong bonding of nanographene to the substrate manifests itself in a high adsorption energy of -12.7 eV and significant charge transfer of 3.46e from the copper surface. Nanographene units coordinated with bromine adatoms are able to arrange in highly regular arrays potentially suitable for nanotemplating