Electronic Structure Theory Group
Research Thrust Areas: Ab-initio calculations in two-dimensional materials
- Excitonic interplay with phonons in bulk and nanoscale semiconductor materials.
- Quasi harmonic analysis like thermal zero point energy computations, temperautre dependent lattice constants, lattice anharmonicities.
- Electrical mobilities in bulk and nanoscale semiconductor materials.
- Nonlinear optical second and third harmonic generations in bulk and nanoscale semiconductor materials.
- Pump-probe and fluences excitonic spectroscopy in bulk and nanoscale semiconductor materials.
- Anamolous Hall effect, anisotropies from self-consistent Hubbard U in magnetic semiconductors and metals.
- SMOKE and MOKE Kerr optical spectra from ferromagteic metals.
Our Works on Calculating Optical Excitations in Famous 2D-Materials
Excitons in monolayers
Excitonic transition weights on the bare electronic energy dispersions of NP monolayer. Bottom row: (d−f) resonant (R1, R2, and R3) excitonic transition weights on the bare electronic energy dispersions. The red areas correspond to the important vertical electronic transitions at the specific excitonic energy. The inset in each case exhibits the exciton weights in the Brillioun zone space. Link
Optical second harmonic generations: Time-dependent BSE
Nonlinear SHG spectra of ML buckled GaAs as function of laser frequencies. Panels (a, c, and e) are the SHG computed using IPA+scissor, TD-DFT, and TD-BSE level of theory, respectively (all are respective absolute values). Panels (b, d, and f) show the absorption spectra computed at ω and ω/2 under the IPA+scissor, TD-DFT, and TD-BSE level of theory, respectively. The open circles are the experimental SHG spectra of zincblende bulk GaAs taken from Bergfeld and Daum and put here for comparison with our monolayer structure. The solid and dashed vertical lines are for the ω and ω/2 gaps. The imaginary and real parts for each of the theory are also presented. From the imaginary part, one can see that SHG goes to zero below half of the band-gap in all the cases. All of these computations were performed on 72×72×1k-point grid. Link
Optical third harmonic generations: Time-dependent BSE
Nonlinear THG spectra of monolayer NP as function of laser frequencies exhibiting the peaks C1, C2, and C3 and C1′, C2′, and C3′ due to the bound excitons B1, B2, and B3 and the resonant exciton R1, R2, and R3, respectively. The x axis is the laser frequency. (b) Absorption spectra at ω and ω/3 under the same TD-BSE level of theory. The vertical dashed line exhibits the ω/3 gap. One can see that χ^(3) goes to zero below one-third of the gap. Link
Density Functional Perturbation Theory
Temperature dependent studies on optical or electronic spectra can be well studied by assessing electron-phonon self energies. These self-energies commonly known as Fan (first order) and Debye-Waller (second order) self-energies and are evaluated from density functional perturbation theory. Image shows Eliashbeg function of monolayer BN. Link
Self-Consistent GW Theory
The dynamic long range electron-electron correlation is responsible for opening the quasi-particle electronic energy gap or simply the G0W0 gap. This essential “salt” is missing in density functional theory that leads to gap underestimation. Image is for GW corrections done on monolayer WSe2. Link
