• VINEET KUMAR RAI

      Articles written in Pramana – Journal of Physics

    • Theoretical study of diaquamalonatozinc(II) single crystal for applications in non-linear optical devices

      MITESH CHAKRABORTY VINEET KUMAR RAI

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      The aim of the present paper is to employ theoretical methods to investigate the zero field splitting (ZFS) parameter and to investigate the position of the dopant in the host. These theoretical calculations have been compared with the empirical results. The superposition model (SPM)with themicroscopic spin-Hamiltonian (MSH) theory and the coefficient of fractional parentage have been employed to investigate the dopant manganese(II) ion substitution in the diaquamalonatozinc(II) (DAMZ) single crystal. The magnetic parameters, viz. $g$-tensor and $D$ tensor, has been determined by using the ORCA program package developed by F Neese $\it{et al}$. The unrestricted Kohn–Sham orbitals-based Pederson–Khanna (PK) as the unperturbed wave function is observed to be the most suitable for the computational calculation of spin–orbit tensor ($D^{SO}$) of the axial ZFS parameter $D$. The effects of spin–spin dipolar couplings are taken into account. The unrestricted natural orbital (UNO) is used for the calculation of spin–spin dipolar contributions to the ZFS tensor. A comparative study of the quantum mechanical treatment of Pederson–Khanna (PK) with coupled perturbation (CP) is reported in the present study. The unrestricted Kohn–Sham-based natural orbital with Pederson–Khanna-type of perturbation approach validates the experimental results in the evaluation of ZFS parameters. The theoretical results are appropriate with the experimental ones and indicate the interstitial occupancy of $\rm{Mn}^{2+}$ ion in the host matrix.

    • Investigation on the electrical and optical properties of some zinc titanate ceramics

      MITESH CHAKRABORTY VINEET KUMAR RAI KUNTAL MITRA

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      The ceramics of spinel zinc orthotitanate (SZT) and perovskite zinc metatitanate (PZT) sintered at $800^{\circ}$C have been prepared using the high-energy ball milling technique. The structural and optical characterisation of the prepared samples has been performed using X-ray diffraction and Fourier transformation of infrared (FT-IR)spectroscopy analysis. The measurements of frequency-dependent dielectric constant of the PZT and SZT ceramics sintered at $800^{\circ}$C have been performed in the $(50−600)^{\circ}$C temperature range. Impedance spectroscopy studies have been reported for the prepared nanocrystalline ceramics. The empirical vibrational frequencies observed from the FT-IR spectra have been compared using the computational method of ORCA program package. Constraints for symmetry, bonds, angles or dihedral angles have not been applied in the geometry optimisation calculations. Hybrid three-parameter exchange-correlation functional of Becke, Lee, Yang, Parr with 20% amount of exact exchange and Ahlrichs triple-zeta valence (def2-TZVP) basis set with polarisation function have been investigated for all atoms without considering the relativistic effects.

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