nan Priyanka

The structural and electronic properties of tubular gold clusters with a spinal support.

Scalar relativistic density functional theory (DFT) is used to investigate the structural and electronic properties of an endohedrally doped hollow tube of gold with a hexagonal cross-section, X(M)Au(N) (X = Si, Al and Au, M = 3, 6, 9 and N = 24, 42, 60). Only Si as a dopant can be encapsulated to provide a stable backbone to the parent tubular Au(N) whereas structures containing an Al or Au backbone are distorted into non-cage like structures as the size increases. The dopant atoms increase the electron density around the Fermi level and shift the d-energy levels to deeper energy levels, thus reducing the HOMO–LUMO gap of the AuN tube. The effect is more pronounced in the Si doped Au(N) than the Al or Au doped Au(N) tubes. The Si9Au60 structure, though stable, shows a slight bending which can be corrected by removing one Si atom from the backbone which provides it with the correct amount of space. It can be concluded that Si and Al atoms can form long chains within the Au nanotube if a gap is present after every 4–6 layers of Au atoms to accommodate the size mismatch between the Si–Si and Al–Al bonds and the Au layers. Si doping within the Au(N) tube is more compatible than Al doping, as confirmed by Mulliken charge analysis.

Structure of Small Gold Clusters with Si Doping Using DFT (AunSi, n=1-10, 19)

The structures of silicon doped gold clusters AunSi (n = 1-10 and 19) have been investigated using first principle calculations based on density functional theory (DFT). Calculations indicate that the stability of a gold cluster increases with the introduction of a Si atom. In all the low lying geometries, Si prefers peripheral positions. For every ground state configuration with n > 3 (n = 6 and 9 being exceptions) Si has tetra-coordination. In almost all of the tetra coordinated geometries the coordination unit including Si, is in the form of a square pyramid with gold atoms forming the square base. Electronic properties such as HOMO-LUMO gap, ionization potential and electron affinity have also been calculated and support the relative stability of clusters with even n. The study of Au20 cage doped with Si atom has been done .Similar to smaller Si doped gold clusters; the Si atom prefers an exohedral position. The doping of Si atom has enhanced the stability and chemical reactivity of Au20 cluster.

A study of various geometries of gold nanowires and effect of doping

We present here the simulations, using Gupta Potential, of gold cylinders under stress, showing the changes leading to the formation of chains at nano level. When one of these short chains is stretched, it transforms from a zigzag configuration to a straight one, passing through various qualitatively different phases and ultimately disintegrating via an interesting ‘dimer’ phase. Strain vs stress for all the cases are presented and young’s modulus calculated. Using Density functional theory (DFT) study we have shown that doping of gold strand with Silicon or Carbon atoms increases its thermodynamic stability as suggested in a recent study.

Monatomic Gold Nanochains and their encapsulation in Au 60 Au 9 tubular structure

Under tensile deformation at 0K, gold nanowires progressively thin through a series of metastable ordered structures such as closed structure bond formations, kinks, Zig - Zag chain, straightening of the chain and then finally leading to its breaking at various stages of stretching possessing both structural and mechanical stabilities. Using atomistic simulations, we study the impact of stretching on the structural evolution of Monatomic gold nanochains (MACs) undergoing elongation along with its application in Tubular gold structure using SIESTA (Spanish Initiative for Electronic Simulation with Thousands of Atoms), the computational code based on Density Functional theory method. In particular, our simulations result in a large number of monatomic chains and intermediate structures.

A comparative study of transition metal doped tubular gold cages:M@Au24(M=Au,Cu,Ag)

A comparative study of endohedral doping of Au24 tubular cage with transition metal M (M= Au, Cu, Ag) has been done using two different methodologies-the density functional theory (DFT) and semi empirical approach using the Gupta potential (GP). The GP predicts Au@Au24 to be the most stable while DFT predicts Cu@Au24 to be the most stable; the Au@Au24 and Ag@Au24 are found to be nearly isoenergetic. The Doping energy and HOMO-LUMO gap from DFT indicate that Cu@Au24-I is chemically most inert.

Stretching of short monatomic gold chains-some model calculations

The Mechanical properties of zig-zag monatomic gold chains containing 5 and 7 atoms were studied using the Siesta Code (SC), which works within the framework of DFT formalism and Gupta Potential (GP), which is an effective atom-atom potential. The zig-zag chains were stretched by keeping the end atoms fixed while rest of the atoms were relaxed till minimum energy is obtained. Energy, Force and Youngs Modulus found using GP and SC were plotted as functions of total length. It is found that the breaking force in case of GP is of order of 1.6nN while for SIESTA is of the order of 2.9nN for both the chains.

Comparison of Cluster Calculation with Different Software—The Case of Small Clusters

The electronic and optical properties of gold clusters Aun of size n = 1 = 15 were examined using a) Gaussian Software (GS) b) Siesta Code (SC). The structural properties were analyzed using GS and SC as well as Gupta Potential. Electronic properties like binding energy per atom (Eb/n), Homo‐Lumo Gap (Eg), ionization potentials, (Adiabatic (AIP)), Chemical Potential(μ), hardness(η) and Softness(S) were investigated using GS and SC within the frame work of DFT formalism. Optical properties like static dipole polarizability of Aun were examined using GS only. Geometry optimization starting from a number of initial geometries were performed for each cluster size and obtained confirmed global minima till size n = 12. Interestingly, for cluster size n, at which 2D to 3D occurs in Aun, different in all different meanslike GS, SC and GP.

Structure and Stability of GeAu{sub n}, n = 1-10 clusters: A Density Functional Study

The structures of Germanium doped gold clusters GeAun (n = 1–10) have been investigated using ab initio calculations based on density functional theory (DFT). We have obtained ground state geometries of GeAun clusters and have it compared with Silicon doped gold clusters and pure gold clusters. The ground state geometries of the GeAun clusters show patterns similar to silicon doped gold clusters except for n = 5, 6 and 9. The introduction of germanium atom increases the binding energy of gold clusters. The binding energy per atom of germanium doped cluster is smaller than the corresponding silicon doped gold cluster. The HUMO‐LOMO gap for AunGe clusters have been found to vary between 0.46 eV–2.09 eV. The mullikan charge analysis indicates that charge of order of 0.1e always transfers from germanium atom to gold atom.