Papers by Puspitapallab Chaudhuri
Journal of Applied Physics, 2020
A nanostructured NiBi 3 /α-Bi 2 O 3 superconductor composite has been synthesized by the process ... more A nanostructured NiBi 3 /α-Bi 2 O 3 superconductor composite has been synthesized by the process of mechanical alloying through 19 h of high energy ball milling. The kinetics of formation is analyzed in detail by x-ray diffraction and the Rietveld method. A simple method is proposed to determine the crystallinity of the resulting sample by using the background Rietveld fitting that permits a quantitative analysis of the diffuse x-ray profile taking into account the air and Compton scattering. The diffuse scattering is attributed to the formation of a nanocluster of α-Bi 2 O 3 which is confirmed by high-resolution transmission electron microscopy and Raman measurements. The magnetic measurements show superconducting transition at around 4 K and the existence of NiBi 3 /α-Bi 2 O 3 nanophases with a low irreversibility field at around 1.01 T at 2 K. Analysis of magnetic susceptibility and isothermal magnetic hysteresis of the NiBi 3 /α-Bi 2 O 3 nanocomposite indicates the simultaneous existence of bulk superconductivity and ferromagnetism below 4 K.
International Journal of Quantum Chemistry, 2017
A detailed and systematic electronic structure calculation has been performed to analyze the hydr... more A detailed and systematic electronic structure calculation has been performed to analyze the hydrogen-bonded interaction of aminoacetonitrile (H 2 NCH 2 CN) with hydrogen cyanide (HCN) and Glycine (H 2 NCH 2 COOH). Both HCN and aminoacetonitrile have already been detected in the interstellar medium (ISM) and their active role in the molecular mechanisms of glycine production has already been recognized. Four different density functional models have been used to study the effect of hydrogen bond formation on the energetic stability and vibrational spectra of the aminoacetonitrile-HCN and aminoacetonitrile-glycine complexes in gas phase. The aminoacetonitrile-glycine dimer is energetically far more stable than all forms of aminoacetonitrile-HCN dimers. Elastic and inelastic scattering of light off the hydrogen-bonded clusters have been investigated in details via Rayleigh and Raman spectroscopic parameters. The dipole moments and depolarization ratios are found to be sensitive on the type of hydrogen-bond network. The mean polarizabilty show appreciable dependence on the choice of the DFT-model. In general, all the chemical groups (OH, CN, NH 2 , and CH) that participate directly in the hydrogen bond formation suffer appreciable variation in the intensity of vibration.
Ab initio methods are used to analyze the structure, energetics and binding energy of the four po... more Ab initio methods are used to analyze the structure, energetics and binding energy of the four possible dipeptides that can be formed from alanine and glycine in gas phase. The structures of the peptides are optimized using Hartree±Fock, second-order Mùller±Plesset perturbation theory and density functional methods (DFT). The effect of electron correlation is analyzed with special emphasis on the calculated binding energies. Single-point energy calculations are performed with CCSD(T) on MP2 geometries to get some additional information on the correlation effects. Electron correlation effects and zero-point vibrational energy corrections increase the binding energy. At the highest level, CCSD(T), we ®nd that the binding energies for alanylalanine, alanylglycine, glycylalanine and glycylglycine are 4.86, 5.09, 5.61 and 5.89 kcal/mol, respectively. These numerical results suggest that glycine donates the OH group easier than alanine. A comparison between the Mùller±Plesset and DFT in different basis sets is made and gives indication of the usefulness of these methods for bio-molecules and peptide formation. Two functionals, B3LYP and B3P86 with different basis sets differing by the systematic inclusion of diffuse and polarization functions, are used in the DFT method. The results obtained using both functionals with a basis that includes both diffuse and polarization functions are in reasonable agreement with the Mùller±Plesset results. However, without including zero-point corrections, some DFT results lead to non-bonding of the peptide molecule.
Density-functional theory calculations of the Rayleigh optical activities of small isolated polyg... more Density-functional theory calculations of the Rayleigh optical activities of small isolated polyglycine molecules are reported. Fully extended b-sheet-like conformations of polypeptides of glycine, (Gly) n (with nZ1-5) are considered. After geometry optimizations, dipole moments and dipole polarizabilities (both the mean and the anisotropic components) are calculated using the B3LYP and B3P86 functionals in three basis sets. The polarizabilities are used to analyze the Rayleigh scattering activities and depolarization ratios. The convergence of the average dipole polarizability per monomer is analyzed. The differences in activity and depolarization for Rayleigh scattered radiation between the extended bsheet-like and the folded a-helix-like forms of tetraglycine are analyzed and found to be relevant, suggesting its possible use in experimental characterization.
Journal of Molecular Structure-Theochem, 2008
The possible ways for glycine oligopeptide formation in gas phase, both in the extended β-strand ... more The possible ways for glycine oligopeptide formation in gas phase, both in the extended β-strand like conformation and folded 27-ribbon like conformations are analyzed using quantum chemical calculations. We focus on the sequential formation of peptide bond through upgradation of the immediate lower order molecule and observe the consequences in other related processes like oligoglycine formation through simultaneous peptide linkage
The effect of aperiodicity on the charge transfer process through DNA molecules is investigated u... more The effect of aperiodicity on the charge transfer process through DNA molecules is investigated using a tight-binding model. Single-stranded aperiodic Fibonacci polyGC and polyAT sequences along with aperiodic Rudin–Shapiro poly(GCAT) sequences are used in the study. Based on the tight-binding model, molecular orbital calculations of the DNA chains are performed and ionization potentials compared, as this might be relevant to understanding the charge transfer process. Charges migrate through the sequences in a multistep hopping process. Results for current conduction through aperiodic sequences are compared with those for the corresponding periodic sequences. We find that dinucleotide aperiodic Fibonacci sequences decrease the current while tetranucleotide aperiodic Rudin–Shapiro sequences increase the current when compared with the corresponding periodic sequences. The conductance in all cases decays exponentially as the sequence length increases.
Physical Review A, 2002
We investigate the scattering of orthopositronium by atomic sodium target at low and medium energ... more We investigate the scattering of orthopositronium by atomic sodium target at low and medium energies ͑up to 50 eV͒ using target-elastic and projectile-elastic close-coupling approximations ͑CCA͒ having different basis sets together with the static-exchange model. The low-energy elastic-scattering parameters are found to be consistent and the estimated binding energy for NaPs ͑in spin-singlet scattering͒ runs from 0.0042-0.0052 a.u. compared to value 0.005 892 a.u. obtained by using stochastic variational method ͓G. Ryzhikh and J. Mitroy, J. Phys. B 31, L401 ͑1998͔͒. The elastic cross sections as obtained by different CCA models, except the static-exchange one, differ very marginally among themselves in the energy range 0.017-25 eV and 15 eV, onwards all the partial cross sections are very close to the corresponding exchange plane-wave estimates. At higher energies ͑above 15 eV͒, it is found that the major contribution to the total cross section comes from the positronium inelastic channels.
The Journal of Physical Chemistry A, 2013
High-level density functional electronic structure calculations have been performed to analyze th... more High-level density functional electronic structure calculations have been performed to analyze the effect of microsolvation with water on the electronic properties of ortho-aminobenzoic acid (o-Abz). The hydrogen-bonded interaction of the o-Abz molecule with one to three water molecules, o-Abz•••(H 2 O) n (n = 1−3), has been considered in two different situations, once the solvent water molecules are placed close to the carboxyl (−COOH) group of o-Abz producing the o-Abz•••⌈H 2 O⌉ n COOH complexes and when the water molecules are placed close to the amino (−NH 2) group producing the o-Abz•••⌈H 2 O⌉ n NH 2 clusters. Variation of the vibrational spectra and energetics upon hydrogen-bond formation are analyzed and compared with available experimental data. The effect of cooperativity is also analyzed. Overall, the hydrogenbonded o-Abz•••⌈H 2 O⌉ n COOH clusters are found to be more stable than the o-Abz•••⌈H 2 O⌉ n NH 2 clusters.
Physical Review A, 2004
This paper reports the elastic scattering cross sections for a few low-lying partial waves and al... more This paper reports the elastic scattering cross sections for a few low-lying partial waves and also the converged elastic cross sections with added partial waves in the energy range 10 Ϫ10-10 Ϫ2 a.u. for the H-H system using atomic orbital techniques. The present s-wave predictions are in good agreement with the other existing theoretical estimates. Nonzero low-order partial-wave elastic cross sections show dips like for s-wave scattering. The converged elastic cross section shows structurelike behavior in the energy range 4.2ϫ10 Ϫ4-10 Ϫ2 a.u.
Physical Review A, 2003
In view of the recent interest in the trapping of antihydrogen atom H , at very low temperatures,... more In view of the recent interest in the trapping of antihydrogen atom H , at very low temperatures, H-H scattering has been investigated at low incident energies using a close-coupling model with the basis set H (1s,2s,2p)ϩH(1s,2s,2p). The predicted s-wave elastic phase shifts, scattering length, and effective range are in a good agreement with the other recent predictions of Jonsell et al. and of Armour and Chamberlain. The results indicate that the atomic orbital expansion model is suitable to study the H-H scattering at ultracold temperatures.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
We present the results of scattering cross sections for positron impact excitation of electronic ... more We present the results of scattering cross sections for positron impact excitation of electronic states of nitrogen molecule (N 2) using the Schwinger multichannel method (SMC). All calculated cross sections took three collision channels into account (X 1 R g and degenerate a 1 P g states). Present theoretical results for excitation to the a 1 P g states failed to reproduce the near-threshold structure observed in the recent and the only available experimental data [Sullivan et al., Phys. Rev. Lett. 87 (2001) 073201-1]. Scattering calculations from the a 1 P g states (elastic and superelastic) are also reported. A spurious resonant structure found in the excitation to the a 1 P g states was detected in a square integrable basis set calculation designed to reproduce the first Born approximation (FBA). Such spurious structure was removed by taking out the trial configuration state functions in which the positron was weakly coupled to the target. This may be a promising technique to separate unphysical resonances from the physical ones. We also observe that a combination between SMC scattering amplitudes (l 6 2) with FBA ones (l P 3) significantly improved the cross sections at higher energies.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
Collisions involving atoms and antiatoms have been investigated at low incident energies using cl... more Collisions involving atoms and antiatoms have been investigated at low incident energies using close-coupling approximation (CCA). We investigate ortho-positroniumortho-positronium (o-Pso-Ps) scattering up to incident energy 3.4 eV. Antihydrogenhydrogen elastic ...
Molecular Physics, 2013
The influence of the hydrogen bond formation on the nuclear magnetic resonance parameters has bee... more The influence of the hydrogen bond formation on the nuclear magnetic resonance parameters has been investigated for the binary (1:1) and ternary (1:2) glycine− HCN complexes in the gas phase using high-level density functional theory with the B3LYP/6-31++G(2d,2p)//B3LYP/ 6-31++G(d,p) model of quantum chemistry. The calculated isotropic/anisotropic shielding parameters of the isolated glycine and HCN molecules are reported and compared with other theoretical results and experimental measurements. Six different conformations of hydrogen-bonded clusters have considered for both 1:1 and 1:2 glycine−HCN complexes. The isotropic and anisotropic chemical shifts for all the constituent atoms of the complexes have been calculated. The spin−spin coupling constants and the Fermi contact terms have also been analyzed in the context of hydrogen-bond formation.
Journal of Physics B: Atomic, Molecular and Optical Physics, 1999
Elastic and inelastic positron-helium scattering have been investigated in different partial wave... more Elastic and inelastic positron-helium scattering have been investigated in different partial waves at medium energies using the close-coupling approximation with realistic wavefunctions employing the following states: He (1s1s), He (1s2s), He (1s2p), He (1s3s), ...
Journal of Physics B: Atomic, Molecular and Optical Physics, 1998
Positronium (Ps) formation in positron-helium scattering has been investigated in different parti... more Positronium (Ps) formation in positron-helium scattering has been investigated in different partial waves at medium energies including the Ore gap region using the close-coupling approximation with realistic wavefunctions for the following states: He(1s1s), He(1s2s), He(1s2p), He(1s3s), He(1s3p), Ps(1s), Ps(2s), Ps(2p). Calculations are reported of rearrangement cross sections to Ps(1s), Ps(2s) and Ps(2p) states for incident positron energies up to 200 eV. The present partial cross sections are in good agreement with experimental results and a variational calculation in the Ore gap region.
Journal of Physics B: Atomic, Molecular and Optical Physics, 1998
The scattering of positrons off sodium targets has been investigated using the coupled static mod... more The scattering of positrons off sodium targets has been investigated using the coupled static model. The sodium atom is represented by the one-active-electron model in which all the electrons of the target have been considered explicitly and the loosely bound valence ...
Journal of Physics B: Atomic, Molecular and Optical Physics, 1997
A narrow S-wave resonance has been found in the positron-helium system at about 30 eV, using the ... more A narrow S-wave resonance has been found in the positron-helium system at about 30 eV, using the close-coupling approach, in excitation and rearrangement cross sections to He (1s2s), He (1s2p), Ps (1s) and Ps (2s) states by employing different combinations of the ...
Journal of Physics B: Atomic, Molecular and Optical Physics, 1999
We derive a closed-form analytic expression in momentum space for the asymptotic non-hydrogenic w... more We derive a closed-form analytic expression in momentum space for the asymptotic non-hydrogenic wavefunction of the quantum defect theory (QDT) due to Seaton and compare it with a widely used QDT-approximate wavefunction for the Rydberg states (2s),(6s) and ( ...
The Journal of Chemical Physics, 2003
Many-body perturbation/coupled-cluster calculations have been carried out to investigate the mult... more Many-body perturbation/coupled-cluster calculations have been carried out to investigate the multiple-body energy terms and their contribution to the interaction energy of linear (HCN)N chains. All minimum energy geometries of the clusters (N=2-7) are obtained at the second-order many-body perturbation (MP2) levels of theory. Electron correlation and cooperative effects in the C-H...N hydrogen bonds are also quantitatively characterized during the aggregation
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Papers by Puspitapallab Chaudhuri