Snehasis Bhunia

Size dependent structural, electronic, and magnetic properties of ScN (N=2-14) clusters investigated by density functional theory

Structural, electronic, and magnetic properties of ScN (N=2-14) clusters have been investigated using density functional theory (DFT) calculations. Different spin states isomer for each cluster size has been optimized with symmetry relaxation. The structural stability, dissociation energy, binding energy, spin stability, vertical ionization energy, electron affinity, chemical hardness, and size dependent magnetic moment per atom are calculated for the energetically most stable spin isomer for each size. The structural stability for a specific size cluster has been explained in terms of atomic shell closing effect, close packed symmetric structure, and chemical bonding. Spin stability of each cluster size is determined by calculating the value of spin gaps. The maximum value for second-order energy difference is observed for the clusters of size N = 2, 6, 11, and 13, which implies that these clusters are relatively more stable. The magnetic moment per atom corresponding to lowest energy structure has also been calculated. The magnetic moment per atom corresponding to lowest energy structures has been calculated. The calculated values of magnetic moment per atom vary in an oscillatory fashion with cluster size. The calculated results are compared with the available experimental data.

Investigation of the encapsulation of metal cations (Cu2+, Zn2+, Ca2+ and Ba2+) by the dipeptide Phe–Phe using natural bond orbital theory and molecular dynamics simulation

AbstractComplexes of the dipeptide phenylalanine–phenylalanine (Phe–Phe) with divalent metal cations (Cu2+, Zn2+, Ca2+ and Ba2+) were studied at the B3LYP and MP2 levels of theory with the basis sets 6-311++G(d,p) and 6-31 + G(d) in the gas phase. The relative energies of these complexes indicated that cation–π bidentate/tridentate conformations are more favourable than other conformations with uncoordinated rings. These findings were confirmed by the calculated values of thermodynamic parameters such as the Gibbs free energy. Natural bond orbital (NBO) analysis was carried out to explore the metal–ligand coordination in Phe–Phe–Cu2+/Zn2+ complexes. Possible orbital transitions, types of orbitals and their occupancies were determined for a range of Phe–Phe–Cu2+/Zn2+ complexes. The charge transfer involved in various orbital transitions was explored by considering the second-order perturbation energy. NBO analysis revealed that the change transfer is stronger when the metal cation uses both the 4s + 4p subshells rather than just its 4p subshell. We also performed molecular dynamics (MD) simulations to check the stability and consistency of the most favourable binding motifs of Cu2+, Zn2+, Ca2+ and Ba2+ with Phe–Phe over time. The structures of the Phe–Phe–Cu2+/Zn2+/Ca2+/Ba2+ complexes obtained using MD simulation were found to be in good agreement with those obtained in the DFT-based calculations. Graphical AbstractConformational search on encapsulation of divalent metal cations (Ca2+, Zn2+, Ca2+, Ba2+) by the Phe-Phe dipeptide

Direct visual evidence of end-on adsorption geometry of pyridine on silver surface investigated by surface enhanced Raman scattering and density functional theory calculations

Fourier transform Raman (FT-Raman) spectra of neat pyridine (Py) and surface enhanced Raman scattering (SERS) spectra of Py with silver nanoparticles (AgNPs) solution at different molar concentrations (X=1.5M, 1.0M, 0.50 M, 0.25 M, and 0.125 M) were recorded using 1064 nm excitation wavelength. The intensity of Raman bands at ∼1003 (ν11) and ∼1035 (ν21) cm(-1) of Py is enhanced in the SERS spectra. Two new Raman bands were observed at ∼1009 (ν12) and ∼1038 (ν22) cm(-1) in the SERS spectra. These bands correspond to the ring breathing vibrations of Py molecules adsorbed at the AgNPs surface. The value of intensity ratios (I12/I11) and (I21/I22) is increased with dilution and attains a maximum value at X=0.5M and upon further dilution (0.25 and 0.125 M) it drops gradually. The theoretically calculated Raman spectra were found to be in good agreement with experimentally observed Raman spectra. Both, experimental and theoretical investigations have confirmed that the Py interacts with AgNPs via the end-on geometry.