Electronic Structure Theory Group

Research Activities: Advanced ab-initio formalisms in semiconductor spectroscopy

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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 is for eliashbeg function done on monolayer BN by us.

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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 by us.

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Optical Absorption Spectra: Bethe-Salpeter Equation

First principles calculations based on the solution of the many-body GW and Bethe-Salpeter equation (BSE) are now a days the most reliable theoretical approach to investigate particle-hole dynamics in crystals. Essentially, the peaks in the photoluminescence spectrum with energy below the gap correspond to bound state electron-hole pairs, known as excitons. Image is for temperature dependent oscillator strength done on monolayer WSe2 by us.

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Real-time Ab-initio Nonlinear Optics

The excitonic spectra within the linear optics can be achieved from the solutionof a time-independent equation of motion (EOM), whereas it needs a solution from the time-dependent EOM to efficiently understand the NL behavior. This leads to real-time dynamics of exciton. Image is for real-time phase-delay bewteen polarization and field done on monolayer GaAs by us.

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