DFT Study on the Spin States of Polyaniline-3d Transition-Metal (Sc-Zn) Composites and Their Sensing Application to Detect Chemical Warfare Agents.

Organic-inorganic composite materials, combining polymers with transition metal (TM) atoms based on PAni and 3d TMs, have been designed and investigated in various spin states by performing density functional calculations. These designed composites were analyzed for their stability in different spin states as well as for their calculated electronic properties, including binding energies, frontier molecular orbitals, and dipole moments. Additionally, 3D isosurfaces and 2D scattered plots of reduced density gradient as a function of (sign λ2)ρ provide insights into the noncovalent interactions between the composite units. The most stable Mn@PAni composite has been assessed as a sensing material for chemical warfare blood agents (HCN, NCCl, NCBr, NCCN, and AsH3) using density functional-based calculations. The reduced band gap and significant red/blue shift in the UV-vis spectra obtained through TDDFT calculations underline the selectivity and efficiency of the Mn@PAni composite toward different analytes.

Encapsulation of heavy metal ions via adsorption using cellulose/ZnO composite: First principles approach.

The primary goal of the current research is to describe an effective and eco-friendly adsorbent for the removal of aquatic micropollutants. The design of the cellulose-modified zinc oxide (ZnO) nanocomposite was successfully carried out by density functional calculations. The proposed structures of the constituent and composite materials were confirmed using formation energy (Ef), frontier orbitals, band gaps (Egap), density of state (DOS) plots, natural bond orbitals (NBO), and UV-Vis spectral analysis. The cellulose/(ZnO)12 composite was further used for the adsorption of different heavy metal ions such as Hg(II), Pb(II), Cd(II), Ni(II), and As(III) through calculation of electronic and optical properties. The values of the adsorption energy (Eads) show that the As(III) interacted better with the composite in both phases, i.e., gas (-806.98 kcal/mol) and aqueous (-491.66 kcal/mol). The analysis of frontier molecular orbital data exhibited a decrease in the Egap of composite@metal ion complexes. The high negative value of the solvation energies (ΔEsol) indicates the suitability of composite@metal ions in an aqueous environment. The nature of interactions between metal ions and the composite unit is analyzed by noncovalent interactions (NCI) and the quantum theory of atoms in molecules (QTAIM). The theoretical results of the present study show the feasibility of the cellulose/(ZnO)12 composite for the removal of heavy metal ions and provide useful information to experimentalists to treat contaminated water.

Properties of Naked Silver Clusters with Up to 100 Atoms as Found with Embedded-Atom and Density-Functional Calculations.

The structural and energetic properties of small silver clusters Agn with n = 2-100 atoms are reported. For n = 2-100 the embedded atom model for the calculation of the total energy of a given structure in combination with the basin-hopping search strategy for an unbiased structure optimization has been used to identify the energies and structures of the three energetically lowest-lying isomers. These optimized structures for n = 2-11 were subsequently studied further through density-functional-theory calculations. These calculations provide additional information on the electronic properties of the clusters that is lacking in the embedded-atom calculations. Thereby, also quantities related to the catalytic performance of the clusters are studied. The calculated properties in comparison to other available theoretical and experimental data show a good agreement. Previously unidentified magic (i.e., particularly stable) clusters have been found for n>80. In order to obtain a more detailed understanding of the structural properties of the clusters, various descriptors are used. Thereby, the silver clusters are compared to other noble metals and show some similarities to both copper and nickel systems, and also growth patterns have been identified. All vibrational frequencies of all the clusters have been calculated for the first time, and here we focus on the highest and lowest frequencies. Structural effects on the calculated frequencies were considered.

Photodegradation of dye using Polythiophene/ZnO nanocomposite: A computational approach.

Incorporating nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. Here, we present density functional theory (DFT) study of Polythiophene/Zinc oxide (PTh/ZnO) nanocomposite with high photocatalytic performance and stability which exhibits superior degradation of alizarine dye under the visible light condition with interaction energy of -149.55 kcal/mol between conducting polymer (PTh) and metal oxide, with PTh sponsoring more number of electrons to the conduction band of ZnO. The electrical and optical properties of optimized geometries of PTh/ZnO nanocomposite were studied by frontier molecular orbital analysis, natural bond orbital (NBO) charge simulation, natural electronic configuration, and UV-vis absorption spectra. The modulation of the energy band gap (∽ 2.60 eV) and exciton binding energy (∽ 0.36 eV) causes visible light absorption and hence enhances the photodegradation activity of PTh/ZnO. NBO analysis evidences the electron accepting behavior of ZnO in the composites as it withdraws electron cloud density of about 0.14e from the polymer unit.

Conceptual DFT and TDDFT study on electronic structure and reactivity of pure and sulfur doped (CrO3)n (n = 1-10) clusters.

Different isomers of (CrO3)n (n = 1-10) cluster units have been investigated using Density functional approach. Their stability and reactivity has been analyzed by plotting chemical potential and HOMO-LUMO gap as a function of cluster size. The CrO3, (CrO3)6 and (CrO3)9 are identified as the most reactive species. Reactivity of each atomic site in the cluster has been interpreted using local reactivity descriptors called Fukui Function plots. The clusters have been doped with sulfur by adding it as substitutional impurity, effect of sulfur doping has been understood by analyzing excitation energies and absorption wavelengths using time dependent-DFT(TDDFT) at CAM-B3LYP level of theory.