In this work, we have used the stochastic search strategy of adaptive mutation simulated annealing (AMSA) as the search tool to explore quantum chemical potential energy to find structures for (Formula presented.) clusters for n up to 8. The evaluated structures are then further refined at higher levels of theories to get more accurate values of IR frequencies, interaction energy (IE), solvation energy (SE) and vertical detachment energy (VDE). The variations of IE, SE and VDE are also observed and critically discussed to understand the observed trends and their correspondence with experimental findings. In a real experimental scenario, where finite temperature is present, any obtained property will be dictated by contribution from local isomers along with the global one. Keeping this important fact in mind, we have investigated conformational populations of different isomers for the atmospherically relevant temperature range between 200 K and 300 K. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.

P NASKAR

R ROY

S TALUKDER

P CHAUDHURY

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.

&nbsp;

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.

&nbsp;

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

Structural, spectroscopic and thermodynamic aspects of azide-water clusters: an approach using a conjugated prescription of stochastic and quantum chemical methods

Molecular Physics

In this communication, we would like to discuss the advantages of adaptive mutation simulated annealing (AMSA) over standard simulated annealing (SA) in studying the Coulombic explosion of (CO2)n2+ clusters for n = 20-68, where 'n' is the size of the cluster. We have demonstrated how AMSA itself can overcome the predicaments which can arise in conventional SA and carry out the search for better results by adapting the parameters (only when needed) dynamically during the simulations so that the search process can come out of high energy basins and not go astray for better exploration and convergence, respectively. This technique also has in-built properties for getting more than one minimum in a single run. For a (CO2)n2+ cluster system we have found the critical limit to be n = 43, above which the attractive forces between individual units become greater in value than that of the large repulsive forces and the clusters stay intact as the energetically favoured isomers. This result is in good concurrence with earlier studies. Moreover, we have studied the fragmentation patterns for the entire size range and we have found fission type fragmentation as the favoured mechanism nearly for all sizes. © The Owner Societies 2017.

Physical Chemistry Chemical Physics

An adaptive mutation simulated annealing based investigation of Coulombic explosion and identification of dissociation patterns in (CO2)N2+ clusters

In this work we obtained global as well as local structures of Br2(-)(H2O)n clusters for n = 2 to 6 followed by the study of IR-spectral features and thermochemistry for the structures. The way adopted by us to obtain structures is not the conventional one used in most cases. Here we at first generated excellent quality pre-optimized structures by exploring the suitable empirical potential energy surface using stochastic optimizer simulated annealing. These structures are then further refined using quantum chemical calculations to obtain the final structures, and spectral and thermodynamic features. We clearly showed that our approach results in very quick and better convergence which reduces the computational cost and obviously using the strategy we are able to get one [i.e. global] or more than one [i.e. global and local(s)] energetically lower structures than those which are already reported for a given cluster size. Moreover, IR-spectral results and the evolutionary trends in interaction energy, solvation energy and vertical detachment energy for global structures of each size have also been presented to establish the utility of the procedure employed. © 2016 the Owner Societies.

An investigation on the structure, spectroscopy and thermodynamic aspects of Br2(-)(H2O): N clusters using a conjunction of stochastic and quantum chemical methods

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 article, we look at the option of using a stochastic optimisation technique, namely genetic algorithm (GA) in association with density functional theory (DFT) to find out the global minimum structures of (MgF2)n clusters with the range of n being between 2 and 10. To confirm whether the structures are indeed the acceptable ones, we go on to evaluate several properties like IR spectroscopic modes, vertical excitation energy, cluster formation energy, vertical ionisation potential and the HOMO-LUMO gap. We stress on the fact that an initial estimation of structure using GA, on two empirical potentials (with and without inclusion of polarisation), leads to a very quick convergence to structures which are quite close to the structures obtained from quantum chemical calculations done from the outset, such as using a DFT calculation. The general structural trend of these systems to form three-dimensional networks is also clear from our study. The lowest energy isomers of these clusters show preference for four-membered Mg2F2 and six-membered Mg3F3 rings. In the IR spectra of (MgF2)n clusters, a blueshift of the Mg-F symmetric stretch and a redshift of asymmetric Mg-F stretching as n increases are obtained. © 2015 Taylor &amp; Francis.

Structure, electronic properties and vibrational spectra of (MgF2)n clusters through a combination of genetic algorithm and DFT-based approach

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

Structural, spectroscopic and thermodynamic aspects of azideâ€“water clusters: an approach using a conjugated prescription of stochastic and quantum chemical methods

Journal	Data powered by TypesetMolecular Physics
Publisher	Data powered by TypesetTaylor and Francis Ltd.
ISSN	0026-8976