@article { ISI:000349902200001, title = {Computational investigation on the catalytic activity of Rh-6 and Rh4Ru2 clusters towards methanol activation}, journal = {Theoretical Chemistry Accounts }, volume = {134}, number = {1}, year = {2014}, month = {DEC}, pages = {1597}, publisher = {SPRINGER}, type = {Article}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Catalysis of molecular activation of small molecules through scission of strong chemical bonds is one of the major challenges faced by chemists. More specifically, activation of the strong C-H and O-H bonds of various alcohols, especially methanol, is one of the various important intermediate steps of key organic reactions. Our present work explores a suitable metal cluster catalyst towards methanol dissociation. In particular, we have examined the effect of ruthenium doping (Rh:Ru = 2:1) on the catalytic activity of Rh-6 cluster towards methanol dissociation. Density functional theory-based calculations illustrate two competitive pathways for methanol dissociation, which are via O-H and C-H bond breaking. Both the pathways are found to be energetically favourable in the presence of bimetallic and mono-metallic clusters. Importantly, energy barrier for O-H bond dissociation reduces considerably in doped cluster as compared to pure Rh-6 cluster and is smaller than the values reported for a number of other small metallic clusters.

}, keywords = {Bimetallic Clusters, Density Functional Theory (DFT), Doping, Methanol Activation, Rhodium Clusters}, issn = {1432-881X}, doi = {10.1007/s00214-014-1597-z}, author = {Ghatak, Kamalika and Sengupta, Turbasu and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000354238700002, title = {Electron attachment to DNA and RNA nucleobases: an EOMCC investigation}, journal = {International Journal of Quantum Chemistry}, volume = {115}, number = {12}, year = {2015}, month = {JUN}, pages = {753-764}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

We report a benchmark theoretical investigation of both vertical and adiabatic electron affinities of DNA and RNA nucleobases: adenine, guanine, cytosine, thymine, and uracil using equation of motion coupled cluster method. The vertical electron affinity (VEA) values of the first five states of the DNA and RNA nucleobases are computed. It is observed that the first electron attached state is energetically accessible in gas phase. Furthermore, an analysis of the natural orbitals exhibits that the first electron attached states of uracil and thymine are valence-bound in nature and undergo significant structural changes on attachment of an extra electron, which reflects in the deviation of the adiabatic electron affinity (AEA) than that of the vertical ones. Conversely, the first electron attached states of cytosine, adenine, and guanine are in the category of dipole-bound anions. Their structure, by and large, remain unaffected on attachment of an extra electron, which is evident from the observed small difference between the AEA and VEA values. VEA and AEA values of all the DNA and RNA nucleobases are found to be negative, which implies that the first electron attached states are not stable rather quasi bound. The results of all previous theoretical calculations are out of track and shows large deviation with respect to the experimentally measured values, whereas, our results are found to be in good agreement. Therefore, our computed values can be used as a reliable standard to calibrate new theoretical methods. (c) 2015 Wiley Periodicals, Inc.

}, keywords = {DNA-RNA bases, electron affinity, EOMCC}, issn = {0020-7608}, doi = {10.1002/qua.24892}, author = {Dutta, Achintya Kumar and Sengupta, Turbasu and Vaval, Nayana and Pal, Sourav} } @article { ISI:000357805700036, title = {Oxidative addition of the C-I bond on aluminum nanoclusters}, journal = {Nanoscale}, volume = {7}, number = {28}, year = {2015}, month = {JUN}, pages = {12109-12125}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Energetics and the in-depth reaction mechanism of the oxidative addition step of the cross-coupling reaction are studied in the framework of density functional theory (DFT) on aluminum nanoclusters. Aluminum metal in its bulk state is totally inactive towards carbon-halogen bond dissociation but selected Al nanoclusters (size ranging from 3 to 20 atoms) have shown a significantly lower activation barrier towards the oxidative addition reaction. The calculated energy barriers are lower than the gold clusters and within a comparable range with the conventional and most versatile Pd catalyst. Further investigations reveal that the activation energies and other reaction parameters are highly sensitive to the geometrical shapes and electronic structures of the clusters rather than their size, imposing the fact that comprehensive studies on aluminum clusters can be beneficial for nanoscience and nanotechnology. To understand the possible reaction mechanism in detail, the reaction pathway is investigated with the ab initio Born Oppenheimer Molecular Dynamics (BOMD) simulation and the Natural Bond Orbital (NBO) analysis. In short, our theoretical study highlights the thermodynamic and kinetic details of C-I bond dissociation on aluminum clusters for future endeavors in cluster chemistry.

}, issn = {2040-3364}, doi = {10.1039/c5nr02278a}, author = {Sengupta, Turbasu and Das, Susanta and Pal, Sourav} } @article { ISI:000354188800009, title = {Relativistic equation-of-motion coupled-cluster investigation of the trends of single and double ionization potentials in the He and Be isoelectronic systems}, journal = {Journal of Physics B-Atomic Molecular and Optical Physics}, volume = {48}, number = {11}, year = {2015}, month = {JUN}, pages = {115009}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {

We employ a four-component spinor relativistic equation-of-motion coupled-cluster (EOMCC) method within the single-and double-excitation approximation to calculate the single ionization potentials (IPs) and double ionization potentials (DIPs) of the He and Be isoelectronic sequences up to Ne. The obtained results are compared with the available results from the National Institute of Standards and Technology (NIST) database to test the performance of the EOMCC method. We also present intermediate results at different levels of approximations in the EOMCC framework to gain insight of the effect of electron correlation. Furthermore, we investigate the dependence of the IPs and DIPs of these ions on the ionic charge and observe that these follow parabolic trends. Similarities between the trends of IPs and DIPs in both the classes of considered systems are categorically demonstrated.

}, keywords = {coupled-cluster method, double ionization potentials, equation-of-motion theory}, issn = {0953-4075}, doi = {10.1088/0953-4075/48/11/115009}, author = {Pathak, Himadri and Sahoo, B. K. and Sengupta, Turbasu and Das, B. P. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000371103000013, title = {Electron detachment and subsequent structural changes of water clusters}, journal = {Journal of Physical Chemistry A}, volume = {120}, number = {7}, year = {2016}, month = {FEB}, pages = {1065-1073}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A cost-effective equation of motion coupled cluster method, EOMIP-CCSD(2), is used to investigate vertical and adiabatic ionization potential as well as ionization-induced structural changes of water clusters and compared with CCSD(T), CASPT2, and MP2 methods. The moderate N-5 scaling and low storage requirement yields EOMIP-CCSD (2) calculation feasible even for reasonably large molecules and clusters with accuracy comparable to CCSD(T) method at much cheaper computational cost. Our calculations shed light on the authenticity of EOMIP-CCSD(2) results and establish a reliable method to study of ionization energy of molecular clusters. We have further investigated the performance of several classes of DFT functionals for ionization energies of water clusters to benchmark the results and to get a reliable functionals for the same.

}, issn = {1089-5639}, doi = {10.1021/acs.jpca.5b09389}, author = {Das, Susanta and Sengupta, Turbasu and Dutta, Achintya Kumar and Pal, Sourav} } @article { ISI:000381418000084, title = {Radical attached aluminum nanoclusters: an alternative way of cluster stabilization}, journal = {Physical Chemistry Chemical Physics}, volume = {18}, number = {31}, year = {2016}, month = {AUG}, pages = {21746-21759}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The stability and electronic structure of radical attached aluminum nanoclusters are investigated using density functional theory (DFT). A detailed investigation shows good correlation between the thermodynamic stability of radical attached clusters and the stability of the attached radical anions. All other calculated parameters like HOMO-LUMO gap and charge transfer are also found to be consistent with the observed thermodynamic stabilities of the complexes. Investigation of the electronic structure of radical attached complexes further shows the presence of jellium structures within the core similar to the ligated clusters. Comparison with available experimental and theoretical data also proves the validity of superatomic complex theory for the radical attached clusters as well. Based on the evaluated thermodynamic parameters, selected radical attached clusters are observed to be more thermodynamically stable in comparison with experimentally synthesized ligated clusters. Stabilization of small metal clusters is one of the greatest challenges in current cluster science and the present investigation confirms the fact that radical attached clusters can provide a viable alternative to ligated clusters in the future.

}, issn = {1463-9076}, doi = {10.1039/c6cp03601e}, author = {Sengupta, Turbasu and Pal, Sourav} } @article { ISI:000375969000054, title = {Transition metal doped aluminum clusters: an account of spin}, journal = {Journal of Physical Chemistry C}, volume = {120}, number = {18}, year = {2016}, month = {MAY}, pages = {10027-10040}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The influence of spin on the properties of small sized transition metal doped aluminum clusters are investigated in the framework of density functional theory (DFT). Detailed analysis on minimum spin doped aluminum clusters has shown prominent indication of odd even oscillation in various calculated properties, supporting the presence of jellium shell structures within them. However, optimized high spin ground state counterparts, on the other hand, show rather smooth trends consistent with the properties of bulk materials. Resemblance to the bulk transition metals is further reflected in the gradual declining trends of heat of adsorption of CO2 molecule on cluster surface by sequentially changing the dopant atom from scandium to zinc. All the observations are also compared and found to be consistent with the earlier theoretical and experimental findings as obtained in the current literature. The similarities in the properties between atomic clusters and the bulk material is of utter importance and indeed precious considering the promising influence of the acquired information in understanding the process of evolution of nanoparticles from constituent atoms.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.6b00510}, author = {Sengupta, Turbasu and Das, Susanta and Pal, Sourav} } @article {43802, title = {Effect of ligand attachment on the C-I bond dissociation process on aluminum nanoclusters: a DFT investigation}, journal = {Journal of Physical Chemistry C}, volume = {121}, year = {2017}, month = {AUG}, pages = {17354-17364}, type = {Article}, abstract = {The influence of the ligand attachment on the activation process of carbon halogen bond on small sized aluminum nanoclusters are investigated using density functional theory. Attaching suitable ligand to metal clusters is among the widely popular techniques often used by experimentalists in order to stabilize metastable clusters. In depth theoretical investigations have shown that based on the jellium configuration of the cluster, attaching an electron withdrawing ligand can either make a cluster more reactive toward the C-I dissociation or may convert the cluster relatively inert. The alteration of the activation barriers and other associated parameters due to ligand attachment are included in this paper along with additional calculations and explanations. The study also shows that even the reaction parameters of specific magic clusters can be significantly altered via ligand attachment. The activation process of small molecules on metal clusters are of crucial importance for the development of material science and cluster chemistry. The present investigation will therefore be useful for better understanding of the properties of the ligated clusters as well as may also aid the experimentalists toward controlling the reactivity of a specific cluster as required.}, doi = {10.1021/acs.jocc.7b05470}, author = {Sengupta, Turbasu and Samanta, Bipasa and Pal, Sourav} } @article {45694, title = {Mechanistic investigation of the carbon-iodine bond activation on the niobium-carbon cluster}, journal = {ACS Omega}, volume = {2 }, year = {2017}, month = {SEP}, pages = {5335-5347}, type = {Article}, abstract = {

The activation process of carbon-iodine (C-I) bond on neutral and cationic niobium metcars (Nb8C12) is investigated using density functional theory and related computational techniques. Metallocarbohedrenes or metcars are a class of stable metal-carbide clusters of specific stoichiometry and of great interest to cluster chemists since their first discovery. The detailed reaction mechanism along with the overall energy profile of the C-I dissociation reaction on niobium metcar and its cations is presented in this paper. The tunneling-corrected rate constants and their related reaction parameters such as the pre-exponential factor are also included alongside. The major differences between the reaction mechanism of the neutral and cationic metcars are also highlighted as well. Despite the available experimental results, the C-I bond dissociation on metcars has remained an unexplored problem in the theoretical and computational domains. Thus, the present investigation can fill in the gap and may also provide new insights provoking further developments in cluster and materials chemistry in future.

}, doi = {10.1021/acsomega.7b00894}, author = {Sengupta, Turbasu and Khan, Muntazir S. and Pal, Sourav} } @article {45378, title = {Specificity of amino acid-aluminum cluster interaction and subsequent oxygen activation by the above complex}, journal = {Journal of Physical Chemistry C }, volume = {122}, year = {2018}, month = {DEC}, pages = {28310-28323}, type = {Article}, abstract = {Amino acid aluminum cluster complex has been shown to be a promising oxygen molecule activator and has the potential to dissociate O-O bond on the cluster surface. The study of the complex also reveals specificity of amino acid to aluminum cluster in the above complex, which can be used in the detection of amino acid. The results have been obtained by the density functional theory at the B3LYP/6-311++g(d,p) level of calculation.}, issn = { 1932-7447}, doi = { 10.1021/acs.jpcc.8b08396}, author = {Samanta, Bipasa and Sengupta, Turbasu and Pal, Sourav} } @article {45538, title = {Aluminum cluster for CO and O-2 adsorption}, journal = {Journal of Molecular Modeling}, volume = {25}, year = {2019}, month = {JAN}, pages = {2}, type = {Article}, abstract = {

Low temperature oxidation of CO to CO2 is an important process for the environment. Similarly adsorption of CO from the releasing sources is also of major concern today. Whereas the potential of gold and silver clusters is well proven for thecatalysis of the above mentioned reaction, the potential of aluminum (Al) clusters remains unexplored. The present study proves that, similar to the transition metals, Al clusters can also be used for adsorption of gases. We first tested the potential of Al cluster as adsorbents for CO. The high binding energy (BE) values prove that Al clusters can be used for adsorbing both CO and O-2. Since oxygen binding is more facile, we adsorbed oxygen on Al and then checked the effect of this O-2 on the BE of CO. The results were obtained by DFT calculations at M062X/TZVP level of theory.

}, keywords = {Aluminum clusters, Charge decomposition analysis, CO adsorption, DFT, O-2 adsorption, Wiberg bond indices}, issn = {1610-2940}, doi = {10.1007/s00894-018-3869-3}, author = {Samanta, Bipasa and Sengupta, Turbasu and Pal, Sourav} }