The problem of constructing reaction paths for conformational changes in noble gas clusters, which are formed by weak dispersion forces has been discussed. The potential energy surface describing these systems are extremely rugged and contains a large number of minima and saddle points within a narrow energy range. So it is not beyond expectation that there must exist a number of paths describing conformational changes in these systems in the given energy range and these bunch of paths provide a better description of possible conformational changes as opposed to the conventional single minimum energy path. To study this issue we have taken up the Ar18 cluster as a typical example and the entire formulation is done with the use of the stochastic search strategy of simulated annealing. The quantitative results clearly show the existence of a large number of minima and transition states and also a multitude of probable transforming paths between stable geometries. © 2017, Springer International Publishing AG.

PINAKI CHAUDHURY

Chemistry

R H MIRDHA

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Journal of Mathematical Chemistry

We present a stochastic optimisation procedure using simulated annealing for studying conformational changes in clusters. The pathways for transformation between stable geometries through a transition state is studied for cluster sizes n=3-12. The work uses an objective function which exploits the sign of the eigenvalues of the Hessian matrix to locate transition states. Once it is located for a specific size it is examined if one minimum geometry can be converted to another through the transition state. The potential energy surface for the system is searched using the stochastic optimisation procedure of simulated annealing. The ruggedness of the surface makes the choice of the optimiser an ideal one. To complete the results the progress of the pathway is depicted as the function of the path coordinates at intermediate geometries. [GRAPHICS] .

Molecular Physics

Constructing transformation paths for conformational changes in (MgF2)(n) clusters using a stochastic procedure

Clusters can exhibit enormous structural diversities and in most cases with the increase in size, the number of conformers that can be supported by the potential energy surface describing the system also increases at a rapid rate. In the present work, this issue has been addressed from the angle of finding out transformation pathways or the so-called reaction paths for interconversion among isomers in (MgO)n clusters, where ‘n’ denotes the size. Clusters with ten different values of ‘n’ starting from 6 and ending at 16 have been studied. For each of these sizes, effort has been made to identify the transition state geometry which connects two minimum configurations. Structural similarities or dissimilarities between the various conformers have been discussed so as to see if any basic unit gets repeated with increase in size of the clusters. The entire study has been conducted using the stochastic optimisation principle of simulated annealing and an adequately defined objective function which can uniquely guide the search towards a first-order saddle point or the transition state on a potential energy surface. © 2017, Springer Science+Business Media, LLC.

Structural Chemistry

Mapping out reaction paths for conformational changes in (M g O)n clusters: a study based on a stochastic procedure

In this communication we would like to explore the idea of obtaining structures and IR spectral features of I2-(H2O)n cluster with n = 2 to 6. The approach taken up by us is a two tire one with initial good quality pre-optimized structures being found out by exploring a suitably constructed empirical potential energy surface and using the stochastic optimizer simulated annealing to explore the surface. These structures are then further refined using quantum chemical calculation to obtain the final structure and the IR spectra. We clearly show that the initial pre-optimization can indeed pave the way for quick and better convergence on subsequent quantum chemical refinement. To give credence to our effort we have also shown the evolutionary trend in vertical detachment energy (VDE) as a function of cluster size. © The Royal Society of Chemistry 2016.

RSC Advances

Structural and spectroscopic studies of iodine dimer radical anion hydrated clusters: An approach using a combination of stochastic and quantum chemical methods

In this paper, we explore the use of stochastic optimizer, namely simulated annealing (SA) followed by density function theory (DFT)-based strategy for evaluating the structure and infrared spectroscopy of (H2O) n OH- clusters where n = 1-6. We have shown that the use of SA can generate both global and local structures of these cluster systems. We also perform a DFT calculation, using the optimized coordinate obtained from SA as input and extract the IR spectra of these systems. Finally, we compare our results with available theoretical and experimental data. There is a close correspondence between the computed frequencies from our theoretical study and available experimental data. To further aid in understanding the details of the hydrogen bonds formed, we performed atoms in molecules calculation on all the global minimum structures to evaluate relevant electron densities and critical points. © 2014 Indian Academy of Sciences.

Fulltext

Journal of Chemical Sciences

Study of structure and spectroscopy of water-hydroxide ion clusters: A combined simulated annealing and DFT-based approach

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. © 2012 Wiley Periodicals, Inc.

Journal of Computational Chemistry

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

In this communication, we would like to test the feasibility of a parallel tempering based study of dissociation in dicationic noble gas clusters, namely, Arn2+, Krn2+, and Xen2+, 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 n2+, 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. © 2013 AIP Publishing LLC.

Journal of Chemical Physics

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

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 2O) nF - 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) © 2011 Wiley Periodicals, Inc.

Journal	Data powered by TypesetJournal of Mathematical Chemistry
Publisher	Data powered by TypesetSpringer International Publishing
ISSN	0259-9791