Vaishali Shah

Density functional investigation of the interaction of acetone with small gold clusters

The structural evolution of Au(n) (n=2, 3, 5, 7, 9, and 13) clusters and the adsorption of organic molecules such as acetone, acetaldehyde, and diethyl ketone on these clusters are studied using a density functional method. The detailed study of the adsorption of acetone on the Au(n) clusters reveals two main points. (1) The acetone molecule interacts with one gold atom of the gold clusters via the carbonyl oxygen. (2) This interaction is mediated through back donation mainly from the spd-hybridized orbitals of the interacting gold atom to the oxygen atom of the acetone molecule. In addition, a hydrogen bond is observed between a hydrogen atom of the methyl group and another gold atom (not involved in the bonding with carbonyl oxygen). Interestingly, the authors notice that the geometries of Au(9) and Au(13) undergo a significant flattening due to the adsorption of an acetone molecule. They have also investigated the role of the alkyl chain attached to the carbonyl group in the adsorption process by analyzing the interaction of Au(13) with acetaldehyde and diethyl ketone.

Ab initio molecular dynamics via density based energy functionals

The use of energy functionals based on charge density as the basic variable is advocated for ab initio molecular dynamics. It is demonstrated that the constraint of positivity of density can be incorporated easily by using the square root of the density for minimization of the energy functional. An ad hoc prescription for including non-local pseudopotentials for plane wave based calculations is proposed and is shown to yield improved results. Applications are reported for equilibrium geometries of small finite systems, viz. dimers and trimers of simple metal atoms like Na and Mg, which represent a rather stringent test for approximate kinetic energy functionals involved in such calculations.

Dzyaloshinskii-Moriya interaction and chiral magnetism in 3d − 5d zigzag chains: Tight-binding model and ab initio calculations

We investigate the chiral magnetic order in freestanding planar 3d-5d biatomic metallic chains (3d :F e, Co; 5d: Ir, Pt, Au) using first-principles calculations based on density functional theory. We find that the antisymmetric exchange interaction, commonly known as the Dzyaloshinskii-Moriya interaction (DMI), contributes significantly to the energetics of the magnetic structure. For the Fe-Pt and Co-Pt chains, the DMI can compete with the isotropic Heisenberg-type exchange interaction and the magnetocrystalline anisotropy energy, and for both cases a homogeneous left-rotating cycloidal chiral spin-spiral with a wavelength of 51 u A and 36 u A, respectively, was found. The sign of the DMI, which determines the handedness of the magnetic structure, changes in the sequence of the 5d atoms Ir(+), Pt(−), Au(+). We use the full-potential linearized augmented plane wave method and perform self-consistent calculations of homogeneous spin spirals, calculating the DMI by treating the effect of spin-orbit interaction in the basis of the spin-spiral states in first-order perturbation theory. To gain insight into the DMI results of our ab initio calculations, we develop a minimal tight-binding model of three atoms and four orbitals that contains all essential features: the spin canting between the magnetic 3d atoms, the spin-orbit interaction at the 5d atoms, and the structure inversion asymmetry facilitated by the triangular geometry. We find that spin canting can lead to spin-orbit active eigenstates that split in energy due to the spin-orbit interaction at the 5d atom. We show that the sign and strength of the hybridization, the bonding or antibonding character between d orbitals of the magnetic and nonmagnetic sites, the bandwidth, and the energy difference between occupied and unoccupied states of different spin projection determine the sign and strength of the DMI. The key features observed in the trimer model are also found in the first-principles results.

Ab initio molecular dynamics using density-based energy functionals: Application to ground-state geometries of some small clusters.

The ground-state geometries of some small clusters have been obtained via ab initio molecular dynamical simulations by employing density-based energy functionals. The approximate kinetic-energy functionals that have been employed are the standard Thomas-Fermi (

An ab initio molecular dynamics investigation of clusters

{\mathit{T}}_{\mathrm{TF}}

Ground-state geometries and the stability of some clusters investigated using density-based ab initio molecular dynamics

) along with the Weizsacker correction

Magnetic properties of 2D nickel nanostrips: structure dependent magnetism and Stoner criterion

{\mathit{T}}_{\mathit{W}}

Electronic structure investigations in conductance across porphyrin-fullerene molecular junctions

and a combination F(

Effect of tautomerism on Au-6-mercaptopurine nanocluster stability

{\mathit{N}}_{\mathit{e}}

Magnetic properties of two dimensional nickel nanowires

)