Publications

We present the first study of photo-induced degradation of PFASs with RT-TDDFT methods. RT-TDDFT calculations show this process is highly selective towards Csingle bondF bond cleavage. RT-TDDFT is a new capability for probing photo-induced degradation of contaminants.

Using GW and Bethe–Salpeter equation simulations, we demonstrate the generation of linearly polarized, anisotropic intra- and interlayer excitonic bound states in the transition metal monochalcogenide (TMC) GeSe/SnS van der Waals heterostructure.

we present a new formulation and implementation of Wannier function-derived Fermi–Löwdin (WFL) orbitals for correcting the self-interaction energies in periodic systems.

We present a new assessment of the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) approach with an emphasis on its performance for predicting energies as a function of fractional occupation numbers (FONs) for various multielectron systems.

Using self-interaction-corrected Born-Oppenheimer molecular dynamics simulations, we provide the first real-time assessment of PFAS degradation in the presence of excess electrons

Using the density functional theoretical calculations, we report a new set of topological semimetals X2YZ, which show the existence of multiple topological triple point fermions along four independent axes. This intermediate linearly dispersive degeneracy between Weyl and Dirac points may offer prospective candidates for quantum transport applications.

Here, we study the interaction of high-intensity pulsed femtosecond laser of various intensities and carrier frequencies with a monolayer phosphorene using the RT-TDDFT. We observe optical Kerr effect associating the changes in the number of free charge carriers with the change in the refractive index of the material, which subsequently characterizes the material’s ability of dielectric switching.

Using first-principles calculations, we study the occurrence of topological quantum phase transitions (TQPTs) as a function of hydrostatic pressure in CdGeSb₂ and CdSnSb₂ chalcopyrites

we report large-scale configuration interaction (CI) calculations of linear optical absorption spectra of various isomers of magnesium clusters Mg_n (n = 2-5), corresponding to valence transitions.

Based on the first-principles calculations, we theoretically propose topologically non-trivial states in a recently experimentally discovered superconducting material CaSn3. When the spin-orbit coupling (SOC) is ignored, the material is a host to three-dimensional topological nodal-line semimetal states.

We benchmark various quantum chemical methods for calculating the optical absorption in planar boron wheel clusters. When compared to the EOM-CCSD spectrum, an excellent agreement is provided by CAM-B3LYP functional, followed by ωB97xD functional.

The first part of the book deals with the mathematical formulation of the solutions of Hartree-Fock equations of electrons confined in multiple centered harmonic oscillator potentials with anharmonic terms present. The interaction among electrons is taken as realistic Coloumb interaction. Confinement at four or more centers can be handled with the present algorithm. The trap geometries can be completely anisotropic. Roothaan procedure is used to convert the integro-differential Hartree-Fock equations to matrix algebra equations. Anharmonicities are expressed as polynomials of position operators. Spin orbit effects can also be taken into account with very little modifications. In the second part, the problem of interacting bosons confined in harmonic oscillator potential and interacting with delta function potential is discussed.The basis functions used in Roothaan expansion are the Harmonic oscillator basis functions.

We report the linear optical absorption spectra of aluminum clusters Aln (n = 2-5) involving valence transitions, computed using the large-scale all-electron configuration interaction (CI) methodology. When compared to the available experimental data for the isomers of Al2 and Al3, our results are in very good agreement as far as important peak positions are concerned. The contribution of configurations to many body wave functions of various excited states suggests that in most cases optical excitations involved are collective, and plasmonic in nature.

We have performed systematic large-scale all-electron correlated calculations on boron Bn, aluminum Aln and magnesium Mgn clusters (n=2–5), to study their linear optical absorption spectra. Several possible isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. Using the optimized ground-state geometries, excited states of different clusters were computed using the multi-reference singles-doubles configuration interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wavefunctions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, eventually leading to their linear absorption spectra. The convergence of our results with respect to the basis sets, and the size of the CI expansion was carefully examined. Isomers of a given cluster show a distinct signature spectrum, indicating a strong structure property relationship. This fact can be used in experiments to distinguish between different isomers of a cluster. Owing to the sophistication of our calculations, our results can be used for benchmarking of the absorption spectra and be used to design superior time-dependent density functional theoretical (TDDFT) approaches. The contribution of configurations to many-body wavefunction of various excited states suggests that in most cases optical excitations involved are collective, and plasmonic in nature. Optical absorption in planar boron clusters in wheel shape, B7, B8 and B9 computed using EOM-CCSD approach, have been compared to the results obtained from TDDFT approach with a number of functionals. This benchmarking reveals that range-separated functionals such as wB97xD and CAM-B3LYP give qualitatively as well as quantitatively the same results as that of EOM-CCSD.

To explore the possibility of achieving a solid-state high-capacity storage of hydrogen for onboard applications, we have performed first-principles density functional theoretical calculations of hydrogen storage properties of beryllium oxide clusters (BeO)n (n = 2-8). The gravimetric density of H2 adsorbed on BeO clusters meets the ultimate 7.5 wt % limit, recommended for onboard practical applications. In conclusion, beryllium oxide clusters exhibit a remarkable solid-state hydrogen storage.

The linear optical absorption spectra in neutral boron cluster B6 and cationic B6 + are calculated using a first principles correlated electron approach. The many-body wavefunctions of various excited states have been analyzed and the nature of optical excitation involved are found to be of collective, plasmonic type. We also benchmark our CIS results against more sophisticated equation-of-motion (EOM) CCSD approach for a few isomers.

The linear optical absorption spectra of three isomers of planar boron cluster B13 are calculated using time-dependent spin-polarized density functional approach. The geometries of these cluster are optimized at the B3LYP/6−311+G* level of theory. Even though the isomers are almost degenerate, the calculated spectra are quite different, indicating a strong structure-property relationship. Therefore, these computed spectra can be used in the photo-absorption experiments to distinguish between different isomers of a cluster.

We have performed systematic large-scale all-electron correlated calculations on boron clusters Bn(n = 2 - 5), to study their linear optical absorption spectra. Several possible isomers of each cluster were considered, and their geometries were optimized at the coupled-cluster singles doubles (CCSD) level of theory. Using the optimized ground-state geometries, the excited states of different clusters were computed using the multi-reference singles-doubles configuration–interaction (MRSDCI) approach, which includes electron correlation effects at a sophisticated level. These CI wave functions were used to compute the transition dipole matrix elements connecting the ground and various excited states of different clusters, eventually leading to their linear absorption spectra.