• Sanjay Kumar

      Articles written in Journal of Chemical Sciences

    • Diabatic potential energy surfaces of H+ + CO

      F George D X Sanjay Kumar

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      Ab initio adiabatic and diabatic surfaces of the ground and the first excited electronic states have been computed for the H+ + CO system for the collinear ($\gamma = 0^\circ$) and the perpendicular (γ = 90°) geometries employing the multi-reference configuration interaction method and Dunning's 𝑐𝑐-𝑝VTZ basis set. Other properties such as mixing angle before coupling potential and before coupling matrix elements have also been obtained in order to provide an understanding of the coupling dynamics of inelastic and charge transfer process.

    • Non-adiabatic collisions in H+ + O2 system: An 𝑎𝑏 initio study

      A Saieswari Sanjay Kumar

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      An $ab$ initio study on the low-lying potential energy surfaces of H+ + O2 system for different orientations (𝛾) of H+ have been undertaken employing the multi-reference configuration interaction (MRCI) method and Dunning's $cc-p$VTZ basis set to examine their role in influencing the collision dynamics. Nonadiabatic interactions have been analysed for the $2 \times 2$ case in two dimensions for 𝛾 = 0°, 45° and 90°, and the corresponding diabatic potential energy surfaces have been obtained using the diabatic wavefunctions and their CI coefficients. The characteristics of the collision dynamics have been analysed in terms of vibrational coupling matrix elements for both inelastic and charge transfer processes in the restricted geometries. The strengths of coupling matrix elements reflect the vibrational excitation patterns observed in the state-to-state beam experiments.

    • Quantum dynamics of vibrational excitations and vibrational charge transfer processes in H+ + O2 collisions at collision energy 23 eV

      Saieswari Amaran Sanjay Kumar

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      Quantum mechanical study of vibrational state-resolved differential cross sections and transition probabilities for both the elastic/inelastic and the charge transfer processes have been carried out in the H+ + O2 collisions at the experimental collision energy of 23 eV. The quantum dynamics has been performed within the vibrational close-coupling rotational infinite-order sudden approximation framework employing our newly obtained quasi-diabatic potential energy surfaces corresponding to the ground and the first excited electronic states which have been computed using ab initio procedures and Dunning’s correlation consistent-polarized valence triple zeta basis set at the multireference configuration interaction level of accuracy. The present theoretical results for elastic/inelastic processes provide an overall agreement with the available state-selected experimental data, whereas the results for the charge transfer channel show some variance in comparison with those of experiments and are similar to the earlier theoretical results obtained using model effective potential based on projected valence bond method and using semi-empirical diatomics-in-molecules potential. The possible reason for discrepancies and the likely ways to improve the results are discussed in terms of the inclusion of higher excited electronic states into the dynamics calculation.

    • Foreword

      Susanta Mahapatra Sanjay Kumar

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    • Ab initio adiabatic and quasidiabatic potential energy surfaces of H++ CN system

      Bhargava Anusuri Sanjay Kumar

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      We present restricted geometry (collinear and perpendicular approaches of proton) ab initio three dimensional potential energy surfaces for H++ CN system. The calculations were performed at the internally contracted multi-reference configuration interaction level of theory using Dunning’s correlation consistent polarized valence triple zeta basis set. Adiabatic and quasidiabatic surfaces have been computed for the ground and the first excited electronic states. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements and coupling potentials.

    • H+ + O2 system revisited: four-state quasidiabatic potential energy surfaces and coupling potentials


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      The global adiabatic and quasidiabatic potential energy surfaces for the ground and first three excited (1−43 A" ) electronic states of H++ O2 system are reported on a finer grid points in the Jacobi coordinates using Dunning’s cc-pVTZ basis set and internally contracted multi-reference (single and double) configuration interaction method. Ab initio procedures have been used to compute the corresponding quasidiabatic surfaces and radial coupling potentials which are relevant for the dynamical studies of inelastic vibrational excitation andcharge transfer processes. Nonadiabatic couplings arising out of relative motion of proton and the vibrational motions of O2 between the adiabatic electronic states have also been analyzed.

    • Ab initio potential energy surface and quantum scattering studies of Li+ with N2: comparison with experiments at Ec.m = 2.47 eV and 3.64 eV


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      A new ground electronic state potential energy surface of Li+ + N2 system is presented in the Jacobi scattering coordinates at MRCI level of accuracy employing the augmented correlation-consistent polarized valence quadrupole zeta (aug-cc-pVQZ) basis set. An analytic fit of the computed ab initio surface has also been obtained. The surface has a global minimum for the collinear geometry at the internuclear distance of N2, r = 2.078a0, and the distance between Li+ and N2, R = 4.96a0. Quantum dynamics studieshave been performed within the vibrational close coupling-rotational infinite-order sudden approximation at Ec.m = 3.64 eV, and the collision attributes have been analyzed. The computed total differential crosssections are found in quantitative agreement with those available from the experiments at Ec.m = 3.64 eV. The other dynamic attributes such as angle dependent opacities and integral cross-sections are also reported.Preliminary rigid-rotor and vibrational–rotational coupled-state calculations at Ec.m.= 2.47 eV also support the experimental observation that the system exhibits a large number of rotational excitations in the vibrational manifold v = 0

    • Understanding the correlation of microscopic structure and macroscopic properties of multi-component glass through atomistic simulations


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      Nuclear power is attracting renewed interest as an alternative power source because it is climate friendly with low greenhouse gas emissions, but its acceptance depends on the safe containment of nuclear waste under geological repositories. For the immobilization of high-level liquid waste (HLLW), borosilicate glass has been considered to be the preferred choice. Selecting suitable glass composition for the vitrification of HLLW is one of the major challenges in nuclear waste reprocessing. The fusion of valuable material properties has led to the acceptance of sodium borosilicate (NBS) glasses for nuclear waste immobilization.The mechanisms associated with these properties are only partially exposed and need further exploration. In that perspective, ZnO doping in borosilicate glasses was studied by performing experiments, classical molecular dynamics (MD), and ab-initio MD (AIMD) simulations. A significant change in glass structure was monitored from short-range order parameters (pair correlation function) and intermediate-range order parameters (angle distribution profiles). Order of connectivity illustrated that the hydrolysis of glass would slow down with the addition of ZnO in the glass matrix. Successively, the effect of microscopic structure on observable glass properties: chemical durability, mechanical strength, and thermal stability, was analyzed. Results show a good match of MD estimated trend for Young Modulus, glass transition temperature, and leaching data with the experimental observations, confirming the transferability of applied potential parameters for multi-component (n≥4) glasses. Both the experiments and MD simulations report the enhanced chemical durability of glass with ZnO addition. The enhanced chemical resistivity of Zn-NBS was also established from the increasing activation energy for the diffusion of Na ions. The combined studies from experiments and atomistic simulations disclose many fascinating microstructures and dynamics due to the presence of ZnO in the glass. The results presented here can be exploited to construe the experimental results and plan future experiments.

      The chemical, mechanical, and thermal strength of ZnO-incorporated sodium borosilicate glass was demonstrated by combined experiments and molecular dynamics (MD) simulations. The BKS interatomic potential was validated by ab-initio MD (AIMD) simulation. The results show the good mapping of MD-generated radial and angle distribution functions with the AIMD results.

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