SSCU

The structures and energetics of nine valence isomers of phosphinine, CH 5 P, have been investigated by ab initio (HF, MP2 and CCSD(T)) and hybrid density functional (B3LYP) methods. The relative stability ordering of the CH 5 P isomers is similar to those of CH 6 . Strain energies are evaluated for all the non-planar isomers based on the sum of standard bond strengths, taking the planar resonance stabilized isomer, phosphinine as the reference. Lower magnitudes of the frequencies corresponding to the ®rst few normal modes compared to their benzene isomers account for smoother isomerization reactions among them. Ó

Hydrogen bonded H· · ·p complexes of C 2 H 2 and C 6 H 6 were studied both computationally and experimentally. Computationally, C 2 H 2 -C 6 H 6 complexes of 1:1 and 2:1 stoichiometries were identified. The molecular structure and stabilisation energies of the complexes were calculated at the HF, MP2, MP2(Full) and B3LYP levels of theory employing basis sets ranging from 6-31G(d,p) and 6-31þþG(d,p) while the frequency calculations were performed at HF, B3LYP and MP2 levels using 6-31G(d,p) and 6-31Gþþ(d,p) basis sets. Using matrix isolation infrared spectroscopy, we observed a 1:1 adduct in an argon matrix. Formation of the adduct was evidenced by shifts in the vibrational frequencies of the acetylene and benzene submolecules in the complex. Though our computations showed two types of 1:1 complexes-one where the acetylene is the proton donor and another where the benzene is the proton donor, experimentally, we observed only the complex, where acetylene acts as a proton donor to the p cloud of benzene. q 2002 Published by Elsevier Science B.V.

Extensive ab initio calculations have been performed using the 6-31G(d,p) and 6-311++G(2d,2p) basis sets for several possible structures of water clusters (H 2 O) n , n ) 8-20. It is found that the most stable geometries arise from a fusion of tetrameric or pentameric rings. As a result, (H 2 O) n , n ) 8, 12, 16, and 20, are found to be cuboids, while (H 2 O) 10 and (H 2 O) 15 are fused pentameric structures. For the other water clusters (n ) 9, 11, 13, 14, and 17-19) under investigation, the most stable geometries can be thought of as arising from either the cuboid or the fused pentamers or a combination thereof. The stability of some of the clusters, namely, n ) 8-16, has also been studied using density functional theory. An attempt has been made to estimate the basis set superposition error and zero-point energy correction for such clusters at the Hartree-Fock (HF) level using the 6-311++G(2d,2p) basis set. To ensure that a minimum on the potential-energy surface has been located, frequency calculations have been carried out at the HF level using the 6-31G(d,p) and 6-311++G(2d,2p) basis sets for some of the clusters. Molecular electrostatic potential topography mapping has been employed for understanding the reactivity as well as the binding patterns of some of the structurally interesting clusters.

The influence of a uniform static external electric field on some aliphatic and aromatic molecular species is studied within the density functional theory (DFT) employing the 6-311++G(2d,2p) basis set with B3LYP exchange-correlation prescription. The electric field perturbs the molecular geometry but drastically alters the dipole moments and engenders, to a varying degree, the molecular vibrational Stark effect, i.e., shifts in the infrared (IR) vibrational frequencies accompanied by spectral intensity redistribution. For polar molecules, significant negative ("red") and positive ("blue") frequency shifts are observed for field orientations both parallel and antiparallel to their permanent dipole moments. Further, a selective reordering of frontier orbitals is observed to be brought about by moderately intense fields. In particular, molecules having a lowest unoccupied molecular orbital (LUMO) with predominant π character possess a threshold field beyond which energy gap between the highest occupied molecular orbital (HOMO) and LUMO diminishes rapidly. A timedependent (TD) DFT analysis reveals that an increase in the applied field strength by and large increases the excitation energies corresponding to significant electronic transitions among frontier MOs with a concomitant decrease in their oscillator strengths.

Quantum chemical investigations are carried out to determine the structure and energetics of anionic water clusters, ðH 2 OÞ n À for n = 8, 10, 12 and 15. Quantum chemical computations performed herein employing a density functional theory (DFT) prescription reveal that these open-shell anionic clusters are metastable in comparison with their neutral analogues. Electron localization of the excess electron in these clusters, traced through molecular electrostatic potential (MESP) and singly occupied molecular orbital (SOMO) density maps, brings out the fact that the excess electron in these clusters is essentially a 'surface' electron i.e. binds externally to the cluster.

It is demonstrated through the present ab initio theoretical investigation that an external electric field can bring about a phenomenal enhancement in the strength of the bond between water and carbon-dioxide molecules from a van der Waals type (binding energy *0.085 eV), to strong covalent type (binding energy *7.45 eV), resulting in an exotic molecular complex. The onset of this effect is characterized by an abrupt change in the dipole moment of the composite system at a particular field-value, concomitant with the O-C=O $ O=C-O resonance in the CO 2 moiety of the complex. This field-induced bond formation is further confirmed by the emergence of a characteristic intermolecular stretching mode (*317 cm -1 ) in the vibrational response of the system. This exotic bond that exhibits a covalent-like character, which accompanied by a charge-transfer, renders the carbon atom a substantial negative charge.

Hydrogen-bonded heteroclusters of H 2 O 2 ‚‚‚(H 2 O) n , with n varying from 1 through 6, have been investigated herein employing ab initio quantum chemical methods. For a given n, several energetically comparable conformers emerge as local minima on the potential energy surface (PES). All of the conformers obtained at restricted Hartree-Fock (RHF) and Møller-Plesset second-order perturbation (MP2) levels of theory exhibit parallel trends in energy hierarchy. The effect of clustering by water on the modification in the vibrational frequencies has also been investigated and further, a many-body interaction-energy analysis is carried out providing insights into cooperativity in H 2 O 2 ‚‚‚(H 2 O) n clusters.

Complex borohydrides have been studied as candidate materials for vehicular hydrogen storage. In particular, M(BH 4) 2 , where M) Mg or Ca, has received considerable attention because of its high gravimetric capacity for H 2. Experimental observations indicate an initial decomposition reaction: 6M(BH 4) 2 f 5MH 2 + MB 12 H 12 + 13H 2 , where the MB 12 H 12 species are amorphous. We use first-principles density functional theory to study the structural and energetic properties of MB 12 H 12. The purpose of these calculations is to investigate why these materials form amorphous structures. We have identified two possible reasons for MB 12 H 12 adopting apparently amorphous rather than crystalline structures. First, our calculations reveal a large number of structurally distinct polymorphs having near-degenerate energies. We simulate an X-ray diffraction (XRD) pattern for each polymorph and compute the Boltzmann-averaged XRD patterns for MgB 12 H 12 and CaB 12 H 12. These average patterns appear to be amorphous, having very broad peaks. Therefore, we predict that the amorphous MB 12 H 12 materials observed experimentally may be an intimate mixture of a very large number of structurally distinct crystallites. Second, our first-principles molecular dynamics calculations indicate that cations are highly mobile near room temperature; analysis of cation radial distribution functions gives liquidlike rather than solid-like features that could also result in an experimental observation of an amorphous XRD pattern near room temperature.

Hydrogen bonded H• • •p complexes of C 2 H 2 and C 6 H 6 were studied both computationally and experimentally. Computationally, C 2 H 2-C 6 H 6 complexes of 1:1 and 2:1 stoichiometries were identified. The molecular structure and stabilisation energies of the complexes were calculated at the HF, MP2, MP2(Full) and B3LYP levels of theory employing basis sets ranging from 6-31G(d,p) and 6-31þþG(d,p) while the frequency calculations were performed at HF, B3LYP and MP2 levels using 6-31G(d,p) and 6-31Gþþ(d,p) basis sets. Using matrix isolation infrared spectroscopy, we observed a 1:1 adduct in an argon matrix. Formation of the adduct was evidenced by shifts in the vibrational frequencies of the acetylene and benzene submolecules in the complex. Though our computations showed two types of 1:1 complexes-one where the acetylene is the proton donor and another where the benzene is the proton donor, experimentally, we observed only the complex, where acetylene acts as a proton donor to the p cloud of benzene.

We consider oxygen interactions with realistic silica surfaces, including both experimentally observed nondefective surface reconstructions and experimentally observed surface defects. Nondefective models include clusters representing the site above a fully coordinated surface Si atom and bridging O atoms, and the defective models include clusters representing an under-coordinated Si defect, a nonbridging O defect, and a ring structure. Energies were obtained for the approach of atomic and molecular oxygen to these clusters in various configurations by using explicitly correlated CCSD(T)-F12b electronic structure theory and the Minnesota density functionals, which were found to be in good agreement. The Minnesota functionals were employed in binding energy calculations for all of the clusters, considering the singlet and triplet spin states for nondefective clusters and doublet and quartet spin states for defective clusters. We find that the chosen defects are energetically favorable sites for binding. The density functional energies were used to extend the empirical ReaxFF SiO potential for silica, which was previously parametrized for bulk silica polymorphs (van Duin et al. J. Phys. Chem. A, 2003, 107, 3803−3811), to model the gas−surface interactions represented by the defective and nondefective clusters presented here. Interaction energy predictions from ReaxFF SiO GSI agree very well with the density functional energies. ReaxFF SiO GSI can now be employed in reactive large-scale molecular dynamics simulations involving oxygen−silica gas−surface interactions such as oxide growth and the heterogeneous recombination of oxygen occurring on real silica surfaces.

Phys. 104, 8821 ͑1996͔͒ at restricted Hartree-Fock ͑RHF͒/MÃ Plesset 2nd order perturbation theory ͑MP2͒/density functional theory ͑DFT͒ level of theory is reported. Use of superior guess density matrices ͑DM's͒ for smaller fragments generated from DM of the parent system and elimination of energetically insignificant higher-body combinations, leads to a more efficient performance ͑speed-up up to 2͒ compared to the conventional procedure. MBAC approach has been tested out on several large-sized weakly bound molecular clusters such as (H 2 O) n , nϭ8, 12, 16, 20 and hydrated clusters of amides and aldehydes. The MBAC results indicate that the amides interact more strongly with water than aldehydes in these clusters. It also reconfirms minimization of the basis set superposition error for large cluster on using superior quality basis set. In case of larger weakly bound clusters, the contributions higher than four body are found to be repulsive in nature and smaller in magnitude. The reason for this may be attributed to the increased random orientations of the interacting molecules separated from each other by large distances.

A novel study on conducting polymers based composites involving hybrid carbon nanostructure assemblage of graphene, amine functionalized multiwalled carbon nanotubes and poly(aniline-co-pyrrole) has been done. The composites were synthesized by oxidative polymerization of 1:1 mixture of aniline and pyrrole monomer with ammonium per sulphate and ferric chloride oxidants. UV-vis Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy were used to identify the chemical structure of the obtained composites. Thermal studies indicate that the composites are stable in comparison to poly (aniline-co-pyrrole) alone showing that the hybrid carbon assemblage contributes towards thermal stability in the composites. Crystalline properties of the composites were investigated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used to characterize the surface morphology of the composites. The specific capacitance of the composites was characterized by cyclic voltammogram (CV). The capacitive studies reveal that the composite has synergistic effect and highest specific capacitance of 337.35F/g at scan rate of 10mV/sec and 193.06F/g at scan rate of 50 mV/sec was obtained for the composite having thinnest layer of co-polymer over hybrid carbon assemblage i.e., 02-PANI-co-PPY-C.

Hierarchical NiCo 2 O 4 /PANI / CNTs hybrid composites were designed and fabricated having a layer of NiCo 2 O 4 on the surface of PANI encapsulated CNTs with different morphologies. Physicochemical attributes of the synthesized composites were examined by FTIR, UV-visible and X-ray diffraction (XRD) techniques. Morphological aspects were evaluated by field-emission scanning microscopy (FESEM), electron diffraction spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies. Electrochemical measurements revealed an improved specific capacitance of 2250 F/g at a scan rate of 5 mV/s and 20 0 0 F/g at a current density of 1 A/g with good rate capability using a three-electrode system. These enhanced features are achieved from the well designed nanostructure and the synergistic contributions of individual components in the electrode material.

One-dimensional nanorod structures of cobalt molybdate, nickel cobalt molybdate and nickel cobalt molybdate/multiwalled carbon nanotube composites have been effectively synthesized by mild hydrothermal method. The elemental analysis of prepared composite nanorods is studied by Fourier transform infrared and electron diffraction X-ray spectroscopy. Structures and morphologies of samples are characterized by X-ray diffraction and field emission scanning electron microscope. SEM morphology authenticates the development of nanorod structures of synthesized samples. The particles' size attained by CoMoO 4 , NiCoMoO 4 and NiCoMoO 4 /CNTs from SEM morphology is in the range of 45-65 nm, 75-85 nm and 100-125 nm. It is experiential that after Ni doping in CoMoO 4 particle size is increased and constituent parts are transformed into consistent dimension with better morphology. The SEM image of NiCoMoO 4 /CNTs shows the threadlike structures that reveal the presence of carbon nanotubes in the composite. EMI shielding measurements were taken using pressed rectangular pellets of 2 mm thickness. The measured total electromagnetic interference (EMI) shielding efficiency (~ SE T) of NiCoMoO 4 /CNTs is 48.84 dB in the Ku band (12.4-18.0 GHz), and involvement of SE due to the absorption of total EMI SE of the composite is larger than that of reflection. This is due to the development of strong conducting network through MWCNTs within divalent transition metal-doped metal-metal matrix. The obtained results suggest the usefulness of the composite for commercial use in far-field EMI shielding and suppression of electromagnetic radiation.

The present study reports the synthesis of a porous Fe-based MOF named MIL-100(Fe) by a modified hydrothermal method without the HF process. The synthesis gave a high surface area with the specific surface area calculated to be 2551 m 2 g −1 and a pore volume of 1.407 cm 3 g −1 with an average pore size of 1.103 nm. The synthesized electrocatalyst having a high surface area is demonstrated as an excellent electrocatalyst for the hydrogen evolution reaction investigated in both acidic and alkaline media. As desired, the electrochemical results showed low Tafel slopes (53.59 and 56.65 mV dec −1), high exchange current densities (76.44 and 72.75 mA cm −2), low overpotentials (148.29 and 150.57 mV), and long-term stability in both media, respectively. The high activity is ascribed to the large surface area of the synthesized Fe-based metal−organic framework with porous nature.

Switching and tuning solid state luminescence properties of molecular materials by modulating molecular packing through non-covalent routes is an attractive prospect. This strategy further makes it feasible to expand the utility of molecules of interest by obtaining a large array of solids-polymorphs, solvates, amorphous phase, nano/micro-crystals and as multi-component systems-with distinct fluorophore arrangement and hence emission characteristics. Because non-covalent interactions that determine the fluorophore arrangements in polymorphs or supramolecular complexes are weak and flexible, their making and breaking become more realistic under ambient conditions, thus having potential to achieve reversible transformations and hence external-stimuli-responsive and switchable molecular fluorescent materials. Recent advances in this context are highlighted in this review with the aid of illustrative examples and further emphasize the scope and relevance of interdisciplinary and multitechnique approaches to unravel the structure-optical property relationships and also to augment the foundations of factual knowledge.

Organic solar cells (OSCs) fabricated from ternary blend thin film absorbers are designed to maximize the range of absorption in the solar spectrum and thus increase the short-circuit current density (JSC) of the device. Herein, we report OSCs formed with two different compositions of ternary blend thin films comprising two electron donors and one acceptor, namely, PTB7-Th/ PCDTBT/IT4F and PTB7-Th/PBDB-T/IT4F. We evaluate the role of Förster resonance energy transfer (FRET) and blend morphology to achieve composition-dependent device performance. We observed ≥10% increment in JSC for both the ternary blends as compared to that for the PTB7Th:IT4F binary blend, resulting in an enhanced power conversion efficiency (PCE) up to 10.34% for the PTB7-Th:PBDB-T:IT4F blend. We provide evidence that the two foremost parameters that control the PCE are blend morphology and FRET between donor components. The improved exciton generation rate for PCDTBT-based ternary blends was achieved, suggesti...