Ngangbam Bedamani Singh

A first principle study of pristine and BN-doped graphyne family

Based on first principle calculation using generalized gradient approximation, we report electronic properties of graphyne and its related structures (graphdiyne, graphyne-3, graphyne-4). Boron and nitrogen atoms are systematically substituted into the position of carbon atom and the corresponding changes of the properties are reported. All the structures are found to be direct band gap semiconductors with band gap depending on the concentration and position of the doping material. Our band structure calculation clearly shows that the band gap can be tuned by B–N doping and the spin-polarized calculation depicts the nonmagnetic nature of these structures. The possibility of modulating the band gap provides flexibility for its use in nanoelectronic devices. Projected density of state (PDOS) analysis shed insights on the bonding nature of these novel materials, whereas from the view point of Crystal Orbital Hamilton Population (–COHP) analysis, the nature of chemical bonding between neighbouring atoms and the orbital participating in bonding and antibonding have been explored in details.

First principle study of adsorption of boron-halogenated system on pristine graphyne

To ensure the possibility of using graphyne as a gas sensor, we have studied the adsorption of boron-halogenated system on pristine graphyne with the help of density functional theory using generalized gradient approximation. Depending on binding energy the most stable orientation, adsorption strength and optimal distance between the above mention molecules and graphyne surface have been determined. The band gap of graphyne slightly increases with the adsorption of the boron-halogenated system. The graphyne system behaves as n-type semiconductor when it interacts with BI3 and BCl3 molecules, and it behaves as p-type semiconductor when interaction with BF3 molecule takes place. Our result reveals that the electronic properties of pristine graphyne are highly influenced by the adsorption of boron-halogenated molecule. We have observed that pristine graphyne has zero electric dipole moment, but with the interaction of boron-halogenated molecule, a significant change in the electric dipole moment takes place. Hence, by measuring the electric dipole moment change, graphyne-based gas sensor can be design for the detection of above-mentioned molecules.

Structure, vibrational, and optical properties of platinum cluster: a density functional theory approach

AbstractUsing density functional theory, stability, chemical, and optical properties of small platinum clusters, Ptn (n = 2 to 10) have been investigated. An attempt has been made to establish a correlation between stability and chemical reactivity parameters. The calculated geometries are in agreement with the available experimental and theoretical results. The atom addition energy change (ΔE1) and stability function (ΔE2) reveal that Pt7 is more stable than its neighboring clusters. Very good agreement of the calculated electron affinity with the available experimental results has been observed. The polarizability of the Ptn clusters depends almost linearly on the number of atoms. A correlation between the static polarizability and ionization potential is found, paving a way to calculate polarizabilty of larger clusters from their ionization potential. The calculated vibrational frequencies are compared with available experimental and theoretical results and good agreement between them has been established. In general, the prominent peak of molar absorption coefficient is shifting toward the lower energy side when cluster size grows. Our DOS calculation suggests that d orbital is primarily responsible for HOMO position and s orbital is responsible for LUMO position. Graphical AbstractStability and reactivity of platinum cluster

A density functional study of chemical, magnetic and thermodynamic properties of small palladium clusters

Structural, chemical, magnetic and thermodynamic properties of palladium clusters Pdn with n = 2–11 are studied using density functional methods. The average bond length, entropy, enthalpy and polarisability are observed to increase as the cluster grows in size. The binding energy per atom also increases with cluster size. Stability function and atom addition energy change predict that Pd4, Pd6 and Pd9 are relatively more stable than their neighbouring clusters. Electron affinity, electronegativity and electrophilicity values suggest that larger clusters have stronger tendency to accept electrons, thereby supporting the relative stability of Pd4 and Pd6. Chemical hardness is also seen to decrease with cluster size, which suggests that large clusters are more prone to changes in their electronic structure. The magnetic properties of these clusters are reported.

Geometry, chemical reactivity and Raman spectra of gold clusters

Abstract Structures, stability, and chemical reactivity of Aun (n = 2-10) clusters are investigated using density functional theory (DFT). We have studied the reactivity parameters of the clusters in terms of relevant electronic structure principles. It is observed that stability and properties are strongly dependent on the cluster size. Clusters with an even number of atoms are found to be energetically and chemically more stable than odd-numbered clusters. Electronic structure of clusters has been investigated using partial density of states (PDOS). PDOS analysis clearly shows that energy states of highest occupied molecular orbital and lowest unoccupied molecular orbital are predominantly contributed by s orbital. From time-dependent DFT calculations, it is shown that absorption spectra of even-numbered clusters are more intense and are observed at lower wavelength region than the odd-sized gold clusters.

Nickel cluster functionalised carbon nanotube for CO molecule detection: a theoretical study

ABSTRACT Using spin-polarised density functional theory calculation single-walled carbon nanotube (SWCNT) whose sidewall is functionalised with nickel cluster is studied for its possible application in CO molecule sensing. We have chosen (6,0) SWCNT functionalised with Ni13 cluster as the model for nanotube-cluster system. Changes in the properties of nanotube-cluster system brought by the CO molecule are reported. The CO molecule binding is energetically more favourable to the nanotube-cluster system than the pristine nanotube. The electronic properties are investigated in terms of density of states and bandstructure calculations. Pristine carbon nanotubes are intrinsically non-magnetic but nanotubes functionalised with nickel cluster are observed to have a huge magnetic moment which reduced on adsorbing CO molecule. The change in magnetisation upon CO adsorption may be detected using a suitable magnetometer. This result suggests the possibility of using carbon nanotube-cluster system to detect CO molecules. Bader charge analysis shows that CO molecule withdraws electronic charge from the cluster atoms. Nature of chemical bonding is studied with crystal orbital Hamilton population (–COHP) analysis.

Investigations of electronic, chemical and non-linear optical properties of para-chloroacetophenone and meta-chloroacetophenone using density functional theory

Quantum chemical calculations of para-chloroacetophenone (p-CAP) and metacholoroacetophenone (m-CAP) are carried out using 6-311++G(d,p) basis set and two different functionals, HF and B3LYP. The structural parameters are in good agreement with the experimental data. The electric dipole moment, polarizability and first hyperpolarizability values of the two selected compounds have been calculated at the same level of theory and basis set and the results shows that the PCAP can be used as a good non linear optical material. The total electron density and molecular electrostatic potential (MEP) surfaces of the molecules were constructed by using B3LYP/6-311++G(d,p) method to display reactive sites for electrophilic and nucleophilic attack.

Tuning the magnetic property of vacancy-defected graphyne by transition metal absorption

In this work, we demonstrate a novel and simple approach to tune the electronic properties as well as magnetic properties of transition metal absorbed in vacancy-defected graphyne (VGY). A double vacancy has been introduced in the graphyne unit and TM atoms (V-Cu) are systematically doped in the vacant site. We find that combination of these two give rise to some interesting spintronics properties such as half-metalicity, and spin-select half-semiconductivity. Furthermore, the magnetic moments of TM absorbed vacancy-defected graphyne are found to be higher compare to TM absorbed graphyne. Although Ni absorbed graphyne is nonmagnetic in nature, we find that the Ni absorbed VGY behaves as half metal with a net magnetic moment of 2 µB and can be used as spin filter. Thus, the TM absorbed vacancy-defected graphyne are more suitable candidate for magneto-optics and spintronics.