## Research

The focus of our research group is development of theoretical and computational methods for accurate treatment of electron-hole interaction in nanomaterial. One of the process by which light interacts with matter is by excitation from ground to excited electronic state. The generation of electron-hole pair or exciton is a quasiparticle representation of electronically excited state of a chemical system. Detailed investigation of electron-hole interaction is important for predicting and understanding optical properties of nanomaterials including quantum dots, quantum rods, nanowires and nanotubes. The electron-hole interaction can be modified using both physical and chemical transformations that provide an excellent opportunity for customization of optical properties of nanomaterials. Our research group is actively developing theoretical methods to investigate effect of size, shape, chemical composition and the surface functionalization on the optical properties of quantum dots and nanoparticles.

### Specific projects

- Electron-hole explicitly correlated method

- Effect of shape and size of quantum dots

- Quantum confined Stark effect

- Effect of core/shell heterojunction in quantum dot

- Diagrammatic summation approach for treating electron correlation

- Nano-bio systems: Quantum dot-protein interactions

- Machine-learning and statistical-learning of quantum mechanical operators

A summary of ongoing projects are listed below:

**Electron-hole explicitly correlated method**: Explicitly correlated wavefunction are explicit function of the electron-hole interparticle distance. The use of explicitly correlated wavefunction is crucial for improving the short-range description of the wavefunction near the electron-hole coalescence point and is importance for calculating accurate electron-hole recombination probabilities and rates. We have developed electron-hole explicitly correlated configuration interaction method (eh-XCCI) for treating electron-hole correlation in nanoparticles. See also: J. Chem. Phys.(2012),
Chem. Phys. Lett.(2012)

**Effect of shape and size of quantum dots**: The optical properties of quantum dots depend strongly on the size and shape of the nanoparticle. We are interested in investigating effect of spatial asymmetry on electron-hole interaction in semiconductor nanoparticles. The goal is to manipulate structure to either enhance or suppress electron-hole recombination for light-harvesting application and solid-state lightening.
See also: J. Chem. Theory Comput.(2013)

**Quantum confined Stark effect**: The effect of external electric fields on the optical properties of quantum dots is known as the quantum confined Stark effect. We are interested applying external electric field to influence electron-hole interaction in quantum dots. In a recent work, we have investigated field-assisted exciton dissociation by including effect of external electric field in electron-hole explicitly correlated configuration interaction method.
See also: J. Chem. Phys.(2013)

**Effect of core/shell heterojunction in quantum dot**: Adding core/shell heterojunction in semiconductor quantum dots can facilitate exciton dissociation and generation of free charge carries. We are interested investigating effect of type-I and type-II heterojunctions on optical properties of quantum dots. See also: JCTC(2015)

**Diagrammatic summation approach for treating electron-electron correlation**: Many-electron wave functions that depend explicitly on
the electron-electron separation distance can be used for treating electron-electron correlation in molecules. However, calculation using explicitly correlated wave function involve computation of 3, 4, 5, and 6-particle operators which add to the computation cost. We are interested in developing diagrammatic summation strategies involving explicitly correlated wave functions for avoiding calculation of many-particle operators. See also: Phys. Rev. A(2012), Phys. Rev. A(2014)

**Nano-bio systems: Quantum dot-protein interactions**: The optical properties of quantum dots are influenced by the presence of surface ligands and one of the applications of this phenomenon is use of quantum dots as nanoprobes in biological systems. We are interested in understanding the effect quantum dot-protein interactions on the optical and electronic properties of the combined nano-bio systems. In a recent work, we investigated the effect of protein corona formation on the optical properties of firefly Luciferase-CdSe quantum dot complex. See also: JCTC(2014)

**Machine-learning and statistical-learning of quantum mechanical operators**: The goal of this work is to learn the
Greenâ€™s function using deep neural networks (DNN) and apply the DNN to calculate ionization enegies of a
series of semiconductor nanoparticles to assess their applicability in photovoltaic and light-harvesting applications
We have developed the Effective Stochastic Potential (ESP) method which represents a thermalized Fock operator in terms of stochastic Gaussian random matrices. The method was used to calculate ensemble-averaged ground and excited state properties of quantum dots.
See also: JCTC(2018), JPCL(2020)