Structure, Carbonyl Vibrational Frequencies, and Local Energy Decomposition of Binding Energy in Formaldehyde Clusters, (HCHO)n=1-10.

In this work, structures, vibrational frequencies, and binding energies of formaldehyde clusters, (HCHO)n=1-10, are investigated by using global optimization genetic algorithm followed by density functional theory calculations and local energy decomposition (LED) analysis at the high-end DLPNO-CCSD(T) level of theory. With the use of genetic algorithm, different structures of all clusters are generated, which are further refined by the quantum chemical geometry optimization technique. From those structures, the conformer with the lowest energy is chosen and used for further analysis. The variation in carbonyl stretching frequency with change in cluster size is discussed and compared with available experimental data. Furthermore, by using standard and advanced LED analysis, different components of the binding energy are studied in all clusters and their variations with cluster size are also discussed.

Investigation of plausible mechanistic pathways in hydrogenation of η5-(C5H5)2Ta(H)=CH2: an analysis using DFT and AIM techniques.

In this manuscript, we investigate two plausible pathways for addition of H2 across the bond Ta=C in η5-(C5H5)2Ta(H)=CH2. One of the investigated reaction pathways involves a single concerted step with a four-membered transition state keeping the oxidation state of tantalum unaltered, where as the other pathway deals with a two step reaction with α-insertion of H2 to produce a 16e⁻ Ta(III)-methyl species and a subsequent oxidative addition. We must emphasize that an experimental study by Bregel et al. [J Am Chem Soc 2002, 124:13827-13832] on a derivative of the investigated chemical system in the present study showed that the two step strategy of α-insertion followed by subsequent oxidative addition is the preferred one. Our numerical investigations using DFT and AIM calculations lead to a similar conclusion. To establish our conclusion, we employ various basis sets to obtain the free energy of activation of the reaction. The AIM technique especially helps us to characterize the bond critical points at the optimized geometries of the reactants, products, transition states, and intermediates for the two step mechanism.

A parallel tempering based study of Coulombic explosion and identification of dissociating fragments in charged noble gas clusters.

In this communication, we would like to test the feasibility of a parallel tempering based study of dissociation in dicationic noble gas clusters, namely, Ar(n)(2+), Kr(n)(2+), and Xe(n)(2+), where "n" is the size of the cluster units. We would like to find out the correct limit for sizes of each of these systems, above which the clusters stay intact as a single unit and does not dissociate into fragments by the process of Coulomb explosion. Moreover, we would also like to, for a specific case, i.e., Ar(n)(2+), study in detail the fragmentation patterns and point out the switchover from the non-fission way to the fission mechanism of dissociation. In all these calculations, we would like to analyse, how close we are in our predictions with that of experimental results. As a further check on the dissociating patterns found out by parallel tempering, we also conduct basin hopping based study on representative sizes of the clusters and find that parallel tempering, as used for this present work as an optimizer, is able to predict correct features when compared with other celebrated methods like the basin hopping algorithm.

Structure and spectroscopic aspects of water-halide ion clusters: a study based on a conjunction of stochastic and quantum chemical methods.

In this article, we propose a stochastic search based method, namely genetic algorithm in conjunction with density functional theory to evaluate structures of water-halide microclusters, with the halide ion being Cl(-), Br(-), and I(-). Once the structures are established, we evaluate the infrared spectroscopic modes, vertical detachment energies and natural population analysis based charges. We compare our results with available experimental and theoretical results.

Structure and spectroscopy of water-fluoride microclusters: a combined genetic algorithm and DFT-based study.

In this article, we explore the efficiency of using a coupled genetic algorithm (GA) and density functional theory (DFT) based strategy to evaluate probable structures of (H(2) O)(n) F(-) micro-clusters, with n = 1 - 6. We use the stochastic optimization technique of GA to arrive at structures of the cluster systems and once the structures are obtained, do a DFT calculation with the optimized coordinates from the GA calculation as input to get the infra-red spectrum of all the systems. The results of our work closely resembles the pure quantum chemical results obtained by Baik et al. (J Chem Phys 1999, 110, 9116-9127).

Types of interaction of meso-tetraphenylporphyrin with alkali and alkaline-earth metal ions.

The cavity in a porphyrin can accommodate metal ions through electron donor-acceptor (EDA) interaction in acetonitrile media without any specially designed fabrication with the porphyrin subunit. Alkali metal ion forms a complex with meso-tetraphenylporphyrin (TP) in 2:1 stoichiometry, while the bivalent Mg(2+) ion follows a 1:1 stoichiometry. A fluorescence interaction study indicated that TP can behave like a chemosensor for these ions present in the blood electrolytes. Specifically, for the alkali metal ions intensity-based sensing was observed, due to inhibition of photoinduced electron transfer (PET), entailing enhancement of fluorescence intensity, and for the alkaline-earth Mg(2+) a mixed quenching was observed. Na(+) and K(+) ions can be differentiated depending upon the extent of fluorescence enhancement.