33 research outputs found
Momentum space properties from coordinate space electron density
Electron density and electron momentum density, while independently tractable
experimentally, bear no direct connection without going through the
many-electron wave function. However, invoking a variant of the
constrained-search formulation of density functional theory, we develop a
general scheme (valid for arbitrary external potentials) yielding decent
momentum space properties, starting exclusively from the coordinate space
electron density. Numerical illustration of the scheme is provided for the
closed-shell atomic systems He, Be and Ne and for singlet
electronic excited state for Helium by calculating the Compton profiles and the
expectation values derived from given coordinate space electron
densities.Comment: 4 pages, 1 figur
Ab initio calculations of structural and electronic properties of CdTe clusters
We present results of a study of small stoichiometric
() clusters and few medium sized non-stoichiometric
[(); ()] clusters using the Density
Functional formalism and projector augmented wave method within the generalized
gradient approximation. Structural properties
{\it viz.} geometry, bond length, symmetry and electronic properties like
HOMO-LUMO gap, binding energy, ionization potential and nature of bonding {\it
etc.} have been analyzed. Medium sized non-stoichiometric clusters were
considered as fragments of the bulk with T{} symmetry. It was observed
that upon relaxation, the symmetry changes for the Cd rich clusters whereas the
Te rich clusters retain their symmetry. The Cd rich clusters develop a
HOMO-LUMO gap due to relaxation whereas there is no change in the HOMO-LUMO gap
of the Te rich clusters. Thus, the symmetry of a cluster seems to be an
important factor in determining the HOMO-LUMO gap.Comment: 8 pages 16 figure
Full potential LAPW calculation of electron momentum density and related properties of Li
Electron momentum density and Compton profiles in Lithium along , and directions are calculated using Full-Potential Linear
Augmented Plane Wave basis within generalized gradient approximation. The
profiles have been corrected for correlations with Lam-Platzman formulation
using self-consistent charge density. The first and second derivatives of
Compton profiles are studied to investigate the Fermi surface breaks. Decent
agreement is observed between recent experimental and our calculated values.
Our values for the derivatives are found to be in better agreement with
experiments than earlier theoretical results. Two-photon momentum density and
one- and two-dimensional angular correlation of positron annihilation radiation
are also calculated within the same formalism and including the
electron-positron enhancement factor.Comment: 11 pages, 7 figures TO appear in Physical Review
First principle study of free and surface terminated CdTe nanoparticles
Density functional calculations of structural and electronic properties
of stoichiometric and nonstoichiometric
CdTe clusters, containing up to few tens of atoms, are carried out
using projector augmented wave method.
Molecular dynamics has been performed
for Cd12Te12 and Cd15Te15
to predict the structure corresponding to global energy minimum.
Cage type structures and bulk fragments, both in zinc blende and
wurtzite structures, are used as starting geometries and
conjugate gradient method is used to locate the local energy minima for other clusters.
The aim of these calculations is to get the energetically favorable probable
structures, to be compared with the experimentally known
structures. Clusters are relaxed both in vacuum and in
the presence of surface passivating ligands and the resulting structural
rearrangement is analyzed. As expected, passivation increases the stability of an
individual cluster, as indicated by specific properties like binding energy,
vertical detachment energy, electron affinity etc.
Passivation also locks the symmetry for three-dimensional structures but the small
CdnTen (1 ≤ n ≤ 6) clusters, which are planar, attain higher
symmetry structures on passivation.
We observe `self-healing' mechanism viz., opening of optical
gap on relaxation without the aid of passivating ligand, in CdTe clusters as
observed in CdSe clusters [A. Puzder et al., Phys. Rev. Lett. 92,
217401 (2004)]. However, we note that 'self-healing' is a stoichiometry dependent
phenomenon. Te atoms are found to achieve a total coordination of 4 on passivation,
a fact useful in chemical synthesis of nanoclusters
Defect studies in small CdTe clusters
We study Cd vacancy formation in prototype stoichiometric and non-stoichiometric
CdTe clusters with and without
passivation. For certain clusters like Cd13Te16,
vacancy leads to severe distortion of the geometry due to propagation
of defect. Annealing of the vacancy out of the cluster is observed in all unpassivated clusters.
Passivated clusters retain their initial geometry and
vacancy induced structural distortions are not seen in
these clusters since the defect gets localized. Vacancy also induces
intragap states. However, it was observed that
the passivation of the dangling bonds created by the vacancy removes the
intragap states. In an attempt to have CdTe clusters with extrinsic carriers,
we substituted a Cd atom by its adjacent atoms Pd/Ag/In/Sn in these CdTe clusters.
Substitutional doping of Cd by metal atoms increases the stability of unpassivated
clusters. For certain clusters, metal atom doping leads to a half-metallic character.
Pd/Ag-doped clusters are p-type semiconductors whereas In-doped clusters are n-type
semiconductors. Sn doping in these clusters does not result in n-type semiconductors
Half-Metallicity in Smallest Cage-like Cluster of CdTe with Doping of Transition Metal Atoms
We report first principles theory based electronic structure studies of a
semiconducting stoichiometric cage-like Cd9Te9 cluster. Substantial changes are
observed in the electronic structure of the cluster on passivation with
fictitious hydrogen atoms, in particular, widening of the energy gap between
highest occupied molecular orbital and lowest unoccupied molecular orbital and
enhancement in stability of cluster is seen. The cluster, when substitutionally
mono-doped for a Cd by a set of 3d and 4d transition metal atoms (Ti, V, Cr,
Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh and Pd), is found to acquire polarization as
seen from spin resolved density of states near Fermi level. Further, such
mono-doping in passivated cluster shows half-metallic behavior. Mapping of
partial density of states of each system on that of undoped cluster reveals
additional levels caused by doping each TM atom separately. In the 3d elemental
doping, Ti and Mn doping result into electron type doping whereas all other
cases result into hole doped systems. For all the 4d elements studied, it is
akin to the doping with holes for Cd substitution in the outer ring, whereas
for Ru and Rh, there is electron type doping in case of substitution for Cd in
central ring upon passivation. A comparison of partial density of states plots
for bare and passivated clusters, on doping with transition metal atoms,
suggests suitability of the cage-like cluster for spintronics applications