My research is primarily concerned with the theory of the electronic structure of atoms, molecules, clusters, and solids. I obtained my Ph. D. in the field of theoretical atomic many-body physics by calculating the electric dipole moment of Rb atom due to various possible parity and time-reversal violating interactions. For the purpose, first principles Dirac-equation-based many-electron calculations were carried out employing state-of-the-art many-body techniques. Furthermore, for my Ph. D. thesis I also developed a coupled-cluster method based linear-response formalism to compute the expectation values of one-electron operators. For my first post-doctoral position at the Idaho National Engineering Laboratory, I worked towards developing relativistic effective core potentials for Dirac equation-based many-electron calculations on atoms. During my post-doctoral years in Max-Planck Institutes in Stuttgart and Dresden, I worked on developing an ab initio formalism for performing many-particle calculations on solids, employing the Wannier functions. During my final post-doctoral position in the University of Arizona during 1998-99, I worked in the field of calculation of the optical properties of conjugated polymers. Ever since I became a faculty member in the Physics Department of I.I.T. Bombay, I have been active in various fields including the electronic structure of solids, polymers, clusters, and graphene, along with studying the properties of dilute trapped atomic gases. The methodology used for the purpose are computational, and several computer codes for the purpose have been developed in our group.