Prasenjit Seal

University Henri Poincare, CRM2, Post-Doc

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I am an independent researcher. I worked at IMDC, UNSW in the field of computational drug delivery and photochemistry. Prior to this, I worked at University of Minnesota and Universite de Lorraine in the field of chemical kinetics and RSH-DFT. My research interest over the years is primarily based on computational chemistry related problems.

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Books by Prasenjit Seal

Aromaticity and Metal Clusters

Papers by Prasenjit Seal

Molecular rearrangement of bicyclic peroxy radicals: key route to aerosol from toluene

Aromatic compounds contribute significantly to the formation of secondary organic aerosol (SOA) t... more Aromatic compounds contribute significantly to the formation of secondary organic aerosol (SOA) that have implications on health and on climate. Toluene is the most abundant aromatic compound in the atmosphere and is emitted through anthropogenic activities such as incomplete combustion and industrial processes. To form SOA, participating vapors such as toluene need to have sufficiently low volatility, which in practice implies molecules with multiple oxygen containing polar functional groups called highly oxygenated organic molecules (HOMs). The oxidation of toluene by OH can lead first to bicyclic peroxy radicals (BPR), and then to HOM. While the formation of HOM has been shown to be efficient, the underlying molecular level mechanism has been challenging to accurately elucidate because of the sheer number of potential pathways. This leads to a major gap in the understanding of the formation of SOA from toluene in the atmosphere. In this work, we conclusively demonstrate for the f...

An aldehyde as a rapid source of secondary aerosol precursors: Theoretical and experimental study of hexanal autoxidation

Aldehydes are common constituents of natural and polluted atmospheres, and their gas-phase oxidat... more Aldehydes are common constituents of natural and polluted atmospheres, and their gas-phase oxidation has recently been reported to yield highly oxygenated organic molecules (HOM) that are key players in the formation of atmospheric aerosol. However, insights into the molecular level mechanism of this oxidation reaction have been scarce. While OH initiated oxidation of small aldehydes, with two to five carbon atoms, under high NO x conditions generally leads to fragmentation products, longer chain aldehydes involving an initial non-aldehydic hydrogen abstraction can be a path to molecular functionalization and growth. In this work, we conduct a joint theoretical-experimental analysis of the autoxidation chain reaction of a common aldehyde, hexanal. We computationally study the initial steps of OH oxidation at the RHF-RCCSD(T)-F12a/VDZ-F12//ωB97X-D/aug-cc-pVTZ level, and show that both aldehydic (on C1) and non-aldehydic (on C4) H-abstraction channels contribute to HOM via autoxidation. The oxidation products predominantly form through the H-abstraction from C1 and C4, followed by fast unimolecular 1,6 H-shifts with rate coefficients 1.7 × 10 −1 s −1 and 8.6 × 10 −1 s −1 , respectively. Experimental flow reactor measurements at variable reaction times show that hexanal oxidation products including HOM monomers up to C 6 H 11 O 7 and accretion products C 12 H 22 O 9−10 form within 3 seconds reaction time. Kinetic modeling simulation including atmospherically relevant precursor concentrations agrees with the experimental results and the expected timescales. Finally, we estimate the hexanal HOM yields up to seven O atoms with mechanistic details through both C1 and C4 channels.

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Cell Membrane Penetration without Pore Formation: Chameleonic Properties of Dendrimers in Response to Hydrophobic and Hydrophilic Environments

Advanced Theory and Simulations, 2020

The mechanism by which cell-penetrating peptides and antimicrobial peptides cross plasma membrane... more The mechanism by which cell-penetrating peptides and antimicrobial peptides cross plasma membranes is unknown, as is how cell-penetrating peptides facilitate drug delivery, mediating the transport of small molecules. Once non-disruptive and non-endocytotic pathways are excluded, pore formation is one of the proposed mechanisms, including toroidal, barrel-stave, or carpet models. Spontaneous pores have been observed in coarse-grained simulations and less often in molecular dynamics simulations. While pores are widely assumed and inferred, there is no unambiguous

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Solving the discrepancy between the direct and relative-rate determinations of unimolecular reaction kinetics of dimethyl-substituted Criegee intermediate (CH3)2COO using a new photolytic precursor

Physical Chemistry Chemical Physics, 2022

Direct kinetic experiments of (CH3)2COO unimolecular reaction using a new photolytic precursor re... more

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Enhancing Cationic Drug Delivery with Polymeric Carriers: The Coulomb‐pH Switch Approach

Advanced Theory and Simulations, 2020

A new coulomb-pH switch method is proposed to enhance the efficient release of cationic drugs und... more A new coulomb-pH switch method is proposed to enhance the efficient release of cationic drugs under acidic conditions occurring near tumor cells or during uptake into cells via endocytosis. The strategy is based on incorporation into the polymeric carrier of both weak acid and weak base functionalities. The consequence of this new design is that the polymeric vector adopts negative charge at physiological pH-facilitating complexation-while at late endosomal pH of 4.5, the polymeric vector adopts a positive charge-promoting highly efficient release of the drug. To illustrate the strategy, molecular dynamics simulations are carried out for a representative system comprising of a peptide dendrimer Gly-Lys(Arg)2 as a model cationic drug and a short poly(4-vinyl imidazole)-b poly(acrylic acid) (PVI-b-PAA) block co-polymer vector. Simulations suggest that these coulomb-pH switch vectors bind the cationic drug effectively at pH = 7.0 and release it decisively once the charge state is changed to reflect pH = 4.5, as indicated by hydrogen bonding, close contact, and distance correlation analyses. Complementary experiments with bespoke synthesized peptide dendrimers indicate that the complexation involves much larger aggregrates than the one-to-one simulation; however unambiguous evidence is provided for the dissolution of the aggregates at pH = 4.5.

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Rationalizing the Aromaticity Indexes Used to Describe the Aromatic Behavior of Metal Clusters

Aromaticity and Metal Clusters, 2010

Rationalizing the Aromaticity Indexes Used to Describe the Aromatic Behavior of Metal Clusters Pr... more Rationalizing the Aromaticity Indexes Used to Describe the Aromatic Behavior of Metal Clusters Prasenjit Seal and Swapan Chakrabarti contents 15.1 What is Aromaticity?................................. ................................................... 297 15.2 Different Indexes of Aromaticity..................................... ...

An experimental and master-equation modeling study of the kinetics of the reaction between resonance-stabilized (CH3)2CCHCH2 radical and molecular oxygen

Physical Chemistry Chemical Physics, 2021

Five-carbon-size allylic radicals are reactive toward O2 under low-temperature combustion conditi... more

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Time-resolved, broadband UV-absorption spectrometry measurements of Criegee intermediate kinetics using a new photolytic precursor: unimolecular decomposition of CH2OO and its reaction with formic acid

Physical Chemistry Chemical Physics, 2020

We present a time-resolved broadband cavity-enhanced UV-absorption spectrometer apparatus that we... more

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Aromaticity and Metal Clusters

AROMATICITY and METAL CLUSTERS, 2010

... obtaining his BSc and MSc from Burdwan University and PhD from IIT ... State Physics and Magn... more

Nonlinear Optical Properties of the Hula Hoop [ n ]‐Cycloparaphenylenes and Their Halo Derivatives at Nd:YAG Laser Frequency

ChemistrySelect, 2017

The present study aims to establish the role of halogen substituents in tuning the nonlinear opti... more The present study aims to establish the role of halogen substituents in tuning the nonlinear optical (NLO) properties of cycloparaphenylenes. We employed time dependent density functional theory as our prime investigating tool to estimate the frequency dependent components of first order hyperpolarizability tensors of these systems at neodymium-doped yttrium aluminium garnet (Nd:YAG) laser frequency. Our results indicate that pristine cycloparaphenylenes have high nonlinear optical properties which corroborates well with reported experimental findings and one can increase this nonlinearity by adding halogen to these species and tuning them as well. This tuning is of great significance as this will allow us to design and synthesize new compounds which have the strong potential to act as NLO materials. Our results also show functional dependence for the NLO tensor components while calculating the NLO properties for molecular systems. The basis set and the solvent effects, however, is not appreciable for the cycloparaphenylenes.

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Binding and Release between Polymeric Carrier and Protein Drug: pH Mediated Interplay of Coulomb forces, Hydrogen Bonding, van der Waals Interactions and Entropy

Biomacromolecules, Jan 7, 2017

The accelerating search for new types of drugs and delivery strategies poses the challenge to und... more The accelerating search for new types of drugs and delivery strategies poses the challenge to understand the mechanism of delivery. To this end, a detailed atomistic picture of binding between the drug and the carrier is quintessential. While many studies focus on the electrostatics of drug-vector interactions, it has also been pointed out that entropic factors relating to water and counter ions can play an important role. By carrying out extensive molecular dynamics simulations and subsequently validating with experiment, we shed light herein on the binding in aqueous solution between a protein drug and a polymeric carrier. We examined the complexation between the polymer, poly (ethylene glycol) methyl ether acrylate-b-poly(carboxyethyl acrylate (PEGMEA-b-PCEA) and the protein, egg white lysozyme, a system that acts as a model for polymer-vector / protein-drug delivery systems. The complexation has been visualized and characterized using contact maps and hydrogen bonding analyses f...

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Dynamical Interactions of 5-Fluorouracil Drug with Dendritic Peptide Vectors: The Impact of Dendrimer Generation, Charge, Counterions, and Structured Water

The Journal of Physical Chemistry B, 2016

Molecular dynamics simulations are utilized to investigate the interactions between the skin canc... more Molecular dynamics simulations are utilized to investigate the interactions between the skin cancer drug 5-fluorouracil (5FU) and peptide-based dendritic carrier systems. We find that these drug-carrier interactions do not conform to the traditional picture of long-time retention of the drug within a hydrophobic core of the dendrimer carrier. Rather, 5FU, which is moderately soluble in its own right, experiences weak, transient chattering interactions all over the dendrimer, mediated through multiple short-lived hydrogen bonding and close contact events. We find that charge on the periphery of the dendrimer actually has a negative effect on the frequency of drug-carrier interactions due to a counter-ion screening effect that has not previously been observed. However, charge is nevertheless an important feature since neutral dendrimers are shown to have a significant mutual attraction that can lead to clustering or agglomeration. This clustering is prevented due to charge repulsion for the titrated dendrimers, such that they remain independent in solution.

A First Principle Framework for Total Charging Energies in Electrocatalytic Materials and Charge-Responsive Molecular Binding at Gas-Surface Interfaces

ACS applied materials & interfaces, May 12, 2016

Heterogeneous charge-responsive molecular binding to electrocatalytic materials has been predicte... more Heterogeneous charge-responsive molecular binding to electrocatalytic materials has been predicted in several recent works. This phenomenon offers the possibility of using voltage to manipulate the strength of the binding interaction with the target gas molecule and thereby circumvent thermochemistry constraints, which inhibit achieving both efficient binding and facile release of important targets such as CO2 and H2. Stability analysis of such charge-induced molecular adsorption has been beyond the reach of existing first-principle approaches. Here, we draw on concepts from semiconductor physics and density functional theory to develop a first principle theoretical approach that allows calculation of the change in total energy of the supercell due to charging. Coupled with the calculated adsorption energy of gas molecules at any given charge, this allows a complete description of the energetics of the charge-induced molecular adsorption process. Using CO2 molecular adsorption onto ...

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Entropic Effects on the Free Energies of Clusters in Silane Plasmas

The Journal of Physical Chemistry C, 2015

The present work demonstrates the importance of entropic effects on the thermodynamics of branche... more The present work demonstrates the importance of entropic effects on the thermodynamics of branched open chain silicon hydride clusters (Si n H m and Si n H m −). These clusters are important constituents in nanodusty silane plasmas. We include all categories of such single-bonded species for n = 5 and 6, namely silyl radicals, silyl anions, silylenes and silylene anions, and silanes. We calculated the statistical mechanical partition functions by employing Kohn−Sham density functional theory with the multistructural method for torsional anharmonicity to estimate thermodynamic quantities, in particular Gibbs free energy, enthalpy, entropy, and heat capacity. For each species we included contributions from all conformational structures of all possible isomers, and we calculated the thermodynamic propeties in three ways, namely by using the multistructural quasiharmonic approximation, the multistructural method with uncoupled torsional potential anharmonicity, and the multistructural method with coupled torsional potential anharmonicity. Our results show that the entropic effects are large and are primarily due to multistructural effects, although torsional potential anharmonicities are not negligible. We find that the multiple-structure effect, which is always greater than unity, is not only very large (as large as a factor of 592) but also very isomer-dependent, so that free energy differences between isomers can be greatly affected. The torsional potential effect is relatively smaller on average but certainly not negligible; it varies from a factor of 0.2 to 1.4.

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Nanodusty plasma chemistry: a mechanistic and variational transition state theory study of the initial steps of silyl anion-silane and silylene anion-silane polymerization reactions

Physical chemistry chemical physics : PCCP, Jan 28, 2015

The growth of nanodusty particles, which is critical in plasma chemistry, physics, and engineerin... more The growth of nanodusty particles, which is critical in plasma chemistry, physics, and engineering. The aim of the present work is to understand the detailed reaction mechanisms of early steps in this growth. The polymerization of neutral silane with the silylene or silyl anion, which eliminates molecular hydrogen with the formation of their higher homologues, governs the silicon hydride clustering in nanodusty plasma chemistry. The detailed mechanisms of these important polymerization reactions in terms of elementary reactions have not been proposed yet. In the present work, we investigated the initial steps of these polymerization reactions, i.e., the SiH4 + Si2H4(-)/Si2H5(-) reactions, and we propose a three-step mechanism, which is also applicable to the following polymerization steps. CM5 charges of all the silicon-containing species were computed in order to analyze the character of the species in the proposed reaction mechanisms. We also calculated thermal rate constant of ea...

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Role of conformational structures and torsional anharmonicity in controlling chemical reaction rates and relative yields: butanal+HO2 reactions

Chemical Science, 2013

Aldehyde-radical reactions are important in atmospheric and combustion chemistry, and the reactio... more Aldehyde-radical reactions are important in atmospheric and combustion chemistry, and the reactions studied here also serve more generally to illustrate a fundamental aspect of chemical kinetics that has been relatively unexplored from a quantitative point of view, in particular the roles of multiple structures and torsional anharmonicity in determining the rate constants and branching ratios (product yields). We consider hydrogen abstraction from four carbon sites of butanal (carbonyl-C, a-C, b-C and g-C) by hydroperoxyl radical. We employed multi-structural variational transition state theory for studying the first three channels; this uses a multi-faceted dividing surface and allows us to include the contributions of multiple structures of both reacting species and transition states. Multi-configurational Shepard interpolation (MCSI) was used to obtain the geometries and energies of the potential energy surface along the minimum-energy paths, with gradients and Hessians calculated by the M08-HX/maugcc-pVTZ method. We find the numbers of structures obtained for the transition states are 46, 60, 72 and 76respectively for the H abstraction at the carbonyl C, the a position, the b position and the g position. Our results show that neglecting the factors arising from multiple structures and torsional

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Kinetics of the Hydrogen Atom Abstraction Reactions from 1-Butanol by Hydroxyl Radical: Theory Matches Experiment and More

The Journal of Physical Chemistry A, 2013

In the present work, we study the H atom abstraction reactions by hydroxyl radical at all five si... more In the present work, we study the H atom abstraction reactions by hydroxyl radical at all five sites of 1-butanol. Multistructural variational transition state theory (MS-VTST) was employed to estimate the five thermal rate constants. MS-VTST utilizes a multifaceted dividing surface that accounts for the multiple conformational structures of the transition state, and we also include all the structures of the reactant molecule. The vibrational frequencies and minimum energy paths (MEPs) were computed using the M08-HX/MG3S electronic structure method. The required potential energy surfaces were obtained implicitly by direct dynamics employing interpolated variational transition state theory with mapping (IVTST-M) using a variational reaction path algorithm. The M08-HX/MG3S electronic model chemistry was then used to calculate multistructural torsional anharmonicity factors to complete the MS-VTST rate constant calculations. The results indicate that torsional anharmonicity is very important at higher temperatures, and neglecting it would lead to errors of 26 and 32 at 1000 and 1500 K, respectively. Our results for the sums of the site-specific rate constants agree very well with the experimental values of Hanson and co-workers at 896-1269 K and with the experimental results of Campbell et al. at 292 K, but slightly less well with the experiments of Wallington et al., Nelson et al., and Yujing and Mellouki at 253-372 K; nevertheless, the calculated rates are within a factor of 1.61 of all experimental values at all temperatures. This gives us confidence in the site-specific values, which are currently inaccessible to experiment.

SixC1−xO2 alloys: A possible route to stabilize carbon-based silica-like solids?

Solid State Communications, 2007

Novel extended tetrahedral forms of CO 2 have been synthesized recently under high-pressure condi... more Novel extended tetrahedral forms of CO 2 have been synthesized recently under high-pressure conditions. We perform ab initio density functional theory calculations to investigate whether doping with Si can extend the stability range of such tetrahedral forms of CO 2 to ambient pressure. Calculations are performed with a simple cubic cell containing eight formula units in a β-cristobalite-like structure. Though we find that all the Si x C 1−x O 2 structures considered by us are thermodynamically unstable with respect to decomposition into the end members at ambient pressures, the energy differences are small, suggesting that it might be possible for such phases to exist in metastable forms. At higher pressures, the heat of formation is found to be negative. The bonding between C and O atoms is more covalent than that between Si and O atoms. We also find indications that some C atoms may prefer threefold coordination at low pressure.

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Large Entropic Effects on the Thermochemistry of Silicon Nanodusty Plasma Constituents

Journal of the American Chemical Society, 2014

Determination of the thermodynamic properties of reactor constituents is the first step in design... more Determination of the thermodynamic properties of reactor constituents is the first step in designing control strategies for plasma-mediated deposition processes and is also a key fundamental issue in physical chemistry. In this work, a recently proposed multistructural statistical thermodynamic method is used to show the importance of multiple structures and torsional anharmonicity in determining the thermodynamic properties of silicon hydride clusters, which are important both in plasmas and in thermally driven systems. It includes five different categories of silicon hydride clusters and radicals, including silanes, silyl radicals, and silenes. We employed a statistical mechanical approach, namely the recently developed multistructural (MS) anharmonicity method, in combination with density functional theory to calculate the partition functions, which in turn are used to estimate thermodynamic quantities, namely Gibbs free energy, enthalpy, entropy, and heat capacity, for all of the systems considered. The calculations are performed using all of the conformational structures of each molecule or radical by employing the multistructural quasiharmonic approximation (MS-QH) and also by including torsional potential anharmonicity (MS-T). For those cases where group additivity (GA) results are available, the thermodynamic quantities obtained from our MS-T calculations differ considerably due to the fact that the GA method is based on single-structure data for isomers of each stoichiometry, and hence lack multistructural effects; whereas we find that multistructural effects are very important in silicon hydride systems. Our results also indicate that the entropic effect on the thermochemistry is huge and is dominated by multistructural effects. The entropic effect of multiple structures is also expected to be important for other kinds of chain molecules, and its effect on nucleation kinetics is expected to be large.

Aromaticity and Metal Clusters

Molecular rearrangement of bicyclic peroxy radicals: key route to aerosol from toluene

An aldehyde as a rapid source of secondary aerosol precursors: Theoretical and experimental study of hexanal autoxidation

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Cell Membrane Penetration without Pore Formation: Chameleonic Properties of Dendrimers in Response to Hydrophobic and Hydrophilic Environments

Advanced Theory and Simulations, 2020

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Solving the discrepancy between the direct and relative-rate determinations of unimolecular reaction kinetics of dimethyl-substituted Criegee intermediate (CH3)2COO using a new photolytic precursor

Physical Chemistry Chemical Physics, 2022

Direct kinetic experiments of (CH3)2COO unimolecular reaction using a new photolytic precursor re... more

Download

Enhancing Cationic Drug Delivery with Polymeric Carriers: The Coulomb‐pH Switch Approach

Advanced Theory and Simulations, 2020

Download

Rationalizing the Aromaticity Indexes Used to Describe the Aromatic Behavior of Metal Clusters

Aromaticity and Metal Clusters, 2010

An experimental and master-equation modeling study of the kinetics of the reaction between resonance-stabilized (CH3)2CCHCH2 radical and molecular oxygen

Physical Chemistry Chemical Physics, 2021

Five-carbon-size allylic radicals are reactive toward O2 under low-temperature combustion conditi... more

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Physical Chemistry Chemical Physics, 2020

We present a time-resolved broadband cavity-enhanced UV-absorption spectrometer apparatus that we... more

Download

Aromaticity and Metal Clusters

AROMATICITY and METAL CLUSTERS, 2010

... obtaining his BSc and MSc from Burdwan University and PhD from IIT ... State Physics and Magn... more

Nonlinear Optical Properties of the Hula Hoop [ n ]‐Cycloparaphenylenes and Their Halo Derivatives at Nd:YAG Laser Frequency

ChemistrySelect, 2017

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Binding and Release between Polymeric Carrier and Protein Drug: pH Mediated Interplay of Coulomb forces, Hydrogen Bonding, van der Waals Interactions and Entropy

Biomacromolecules, Jan 7, 2017

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Dynamical Interactions of 5-Fluorouracil Drug with Dendritic Peptide Vectors: The Impact of Dendrimer Generation, Charge, Counterions, and Structured Water

The Journal of Physical Chemistry B, 2016

A First Principle Framework for Total Charging Energies in Electrocatalytic Materials and Charge-Responsive Molecular Binding at Gas-Surface Interfaces

ACS applied materials & interfaces, May 12, 2016

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Entropic Effects on the Free Energies of Clusters in Silane Plasmas

The Journal of Physical Chemistry C, 2015

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Nanodusty plasma chemistry: a mechanistic and variational transition state theory study of the initial steps of silyl anion-silane and silylene anion-silane polymerization reactions

Physical chemistry chemical physics : PCCP, Jan 28, 2015

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Role of conformational structures and torsional anharmonicity in controlling chemical reaction rates and relative yields: butanal+HO2 reactions

Chemical Science, 2013

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Kinetics of the Hydrogen Atom Abstraction Reactions from 1-Butanol by Hydroxyl Radical: Theory Matches Experiment and More

The Journal of Physical Chemistry A, 2013

SixC1−xO2 alloys: A possible route to stabilize carbon-based silica-like solids?

Solid State Communications, 2007

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Large Entropic Effects on the Thermochemistry of Silicon Nanodusty Plasma Constituents

Journal of the American Chemical Society, 2014

Kinetics of the Hydrogen Abstraction from Carbon-3 of 1-Butanol by Hydroperoxyl Radical: Multi-Structural Variational Transition-State Calculations of a Reaction with 262 Conformations of the Transition State

The Journal of Physical Chemistry Letters, 2012

We estimated rate constants for the hydrogen abstraction from carbon-3 of 1-butanol by hydroperox... more We estimated rate constants for the hydrogen abstraction from carbon-3 of 1-butanol by hydroperoxyl radical, a critically important reaction in the combustion of biofuel. We employed the recently developed multi-structural variational transition-state theory (MS-VTST), which utilizes a multifaceted dividing surface that allows us to include the contributions of multiple structures for reacting species and transition states. First, multiconfigurational Shepard interpolation-based on molecular-mechanics-guided interpolation of electronic-structure Hessian data obtained by the M08 HX/jun-cc-pVTZ electronic model chemistry-was used to obtain the portion of the potential energy surface needed for single-structure variational transition-state theory rate constants including multidimensional tunneling; then, the M08-HX/MG3S electronic model chemistry was used to calculate multi-structural torsional anharmonicity factors to complete the MS-VTST rate constant calculations. The lowest-energy structures of the transition state have strongly bent hydrogen bonds. Our results indicate that neglect of multi-structural anharmonicity would lead to errors of factors of 0.3, 46, and 171 at 200, 1000, and 2400 K for this reaction.

Range Separated Hybrid Density Functional Theory (RSHDFT): A novel scheme to model weak interactions

Although density functional theory (DFT) is the most widely used and one of the powerful methods ... more Although density functional theory (DFT) is the most widely used and one of the powerful methods for electronic structure calculations, yet it fails to properly model the interactions present between weak van der Waals complexes. The main reason behind this is the incapability of the DFT functionals in describing long-range electron correlations which are present in these weakly bound complexes. Several approaches have been implemented in order to overcome this deficiency amongst which the idea proposed by Savin gains a lot of importance. In this approach, the electron operator is separated into short- and long-range parts using error function in the following way.

where, erf is the error function, is for coordinate vectors of electrons, and and μ is a range-separation parameter which determines the ratio of short and long-range parts. The scheme described above is often known by the term Range-Separated Hybrid (RSH) formalism. In the RSH scheme, the long-range exchange and correlation is treated explicitly by Hartree-Fock method and other approaches like MP2, Random Phase Approximation (RPA), coupled-cluster theory, CI techniques etc., respectively. This approach quite often gives promising results, particularly, for rare-gas dimers and some molecular complexes. The focus of the present study is to benchmark the performance of different RSH+ variants in describing non covalent interactions in different categories of systems. Of particular interest is the RPA approach, used to obtain the long-range correlation energies. The RPA approach is implemented here via the adiabatic-connection fluctuation-dissipation theorem (ACFDT) based on the range separation of electron-electron interactions. Our results suggest that in almost all the cases where RSH method combines with RPA schemes (RSH + RPA/RPAx), it yields the best results amongst all the other methods to describe weak-interactions.

Electrionic structure calculations of some molecules and small clusters with special emphasis on optical and magnetic properties

One of the major issues in the field of electronic structure calculations is to understand the re... more One of the major issues in the field of electronic structure calculations is to understand the relationship of different electronic properties of materials with their structure or composition. This interesting area is enriched with several electronic structure methods, which are used for performing the calculations. The major advantage of electronic structure calculation is its reliability whenever any given physical property becomes physically inaccessible. The presentation will mainly focus on two rapidly emerging field of interest – optical and magnetic properties. The systems, which we deal with, are DNA base pairs, alkali metal doped clusters, photochromic pair of molecules and CdnTen clusters for describing the optical properties. The magnetic properties are studied in some six-membered heteroatomic systems and four-membered A2B2 clusters including metal atoms. The magnetic interactions in some interesting diradicals have also been addressed. For calculating the above-mentioned properties, we rely ourselves to density functional theory, configuration interaction approach via singles and Møller- Plesset perturbation theory. In the optical property section, some of the systems under investigation are quite relevant in the context of designing future generation devices for various technological applications. It has been observed that there are several factors that are responsible for influencing the optical properties in these systems. These include Hbonding in DNA base pairs, basis set effect, effect of solvent polarity in photochromic pair, role of electron correlation in CdnTen clusters. A proper theoretical justification is what we tried to offer here. In dealing with the magnetic properties, we came across the widely known phenomenon of aromaticity. The reliability of nucleus independent chemical shift (NICS) scanning in explaining aromatic behavior in some well-known sixmembered heteroatomic systems and four-membered A2B2 heteroatomic clusters are discussed. Our results reveal that NICS scanning can only be used for the heteroatomic systems if and only if some other aromaticity descriptors accompany it. The strength of magnetic interactions in diradicals is also highlighted. The investigations indicate the role of alkyl substituents and H-bonding in influencing the strength of the magnetic interactions in alkyl-substituted cyclohexane diyls and dehydrogenated Guanine-Cytosine (GC) base pairs or the GC diradicals, respectively.

Explicit Role of Dynamic and Nondynamic Electron Correlation on C4N+2 Clusters

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