I started my research work focusing on the development of exchange-correlation functionals for the ground and excited states within DFT. In my thesis work, I have paid attention to developing several exchange-correlation density functionals to accurately describe the ground-state properties of the materials. For further exploration, I have been involved in the development of new DFT based methodologies aimed at making a more accurate description of the phenomena related to the novel materials properties involving the ground and excited states in various physics and chemical processes. Currently, I am working on the development of the versatile and accurate meta-generalized gradient approximation to be used in studying molecular and material properties from bulk to nanoscale systems. Not only that, but I am also involved in the development of compatible van der Waals interactions of the above developed semilocal density functionals within quantum simulation regime.

I am also actively working to develop screened hybrid functionals based on the accurate semilocal level functionals (like SCAN and TM based methods). This has been tested for the well known basic properties of the solids but not extensively tested for the more complicated solid-state properties. The first principle MD simulation of materials using the developed methods is also an ongoing research activity. Studying the developed methodology shows very promising results in many solid-state properties which can be further explored to study the novel properties of materials which are still a challenge within the GGA level semilocal and hybrid functional. I believe that our developed methods serve the community to better understand the material properties with relevant applications. If necessary I will also focus on the implementation of the dielectric dependent meta-GGA hybrids, linear response, and random phase approximation (RPA) , Green functional techniques (GW), and Bethe-Salpeter equation (BSE) based methods. My secondary interest also focuses on the orbital-free density functional theory (OFDFT), weighted density functional theory (WDFT), constrained density functional theory (CDFT), and adiabatic connection (AC) methods.

Dimensionality is one of the most defining material parameters. As a result, chemical compounds can exhibit dramatically different properties depending on their arrangement in zero dimension (0D), one dimension (1D), two dimensions (2D), or three dimensions (3D) bulk structure. Although quasi-0D e.g., cage molecules, quasi-1D e.g., nanotubes, and 3D objects are extensively studied, 2D materials are now achieving increased interest among these classes of materials. Atomically thin (i.e. quantum systems) 2D materials, such as graphene, hexagonal boron-nitride, transition-metal dichalcogenides (TMDCs), and phosphorene are presently being researched because of their unique electronic properties. Individual 2D layers, constituting a 2D flatland, are held together by a van der Waals (vdW) force to form 2D vdW heterostructure. In general, these 2D vdW quantum systems are stable under ambient conditions, exhibit high crystal quality, and are continuous on a macroscopic scale suitable for many technological functionalities. My research interest involves topological surface effect, transport properties, proximity induced behavior, band offset, and magnetism in vdW heterostructure. In particular, we focus on the TMDC like semiconducting systems with insulator heterostructure (such as h-BN and MoS2) to study those properties. Systems like phosphorene sandwiched between TMDC are also my present and future interest. We apply a very accurate density functional approach to study the material properties.

Examine high-pressure phases of solids, mainly semiconductors, and 2D vdW solids are a growing field. Density functional theory vastly use for accurate prediction of the solids under pressure. Not only theoretical but also experimental studies are available there. Different levels of density functional methods are applied to study the III-V structural phase transition of semiconductors. Despite successful implementations of semilocal approximations for solids, there are certain challenging cases for which the performance of the semilocal functional approximation is not up to the mark, even for the most advanced and promising semilocal approach. For example, the structural phase transition of the polymorphs of FeS2 (pyrite and marcasite polymorphs) and TiO2 (rutile and anatase polymorphs) possesses challenges for ab-initio density functional calculations. Note that all these systems quite emerging materials due to their important properties and having industrial applications. However, accurate prediction of these challenging systems is assessable from the advanced meta-generalized gradient approximations we developed. Further investigation and assessment of these methods for a large class of solids including the vdW solids are ongoing research projects.

Optical properties of organic solar cells, organic-inorganic hybrids, and vdW heterostructures are emerging fields and attracting significant interest. Time-dependent density functional theory (TDDFT) is the standard tool to investigate those systems. However, there possess challenges. A recent study shows the TD optimally tuned range-separated hybrids are quite successful in predicting the accurate optical spectra. The accuracy of these levels is close to the highly expensive BSE methods. Besides hybrids density levels, TDDFT kernels by including the ultra-long-range behavior are also introduced. But those are developed only for bulk solids. In this project, we focus on the accurate optical properties prediction of the organic-inorganic hybrids, vdW heterostructures, and molecular clusters by developing low-cost semilocal methods.

Accurate prediction of water properties in its gas and condensed phases, including the interaction of water with surfaces, is of prime importance for many scientific and industrial disciplines. Though wave functional methods like CCSD(T), MP2, and RPA are successful, they are quite costly for large systems, especially, for water-solids interactions. In our recent study, we show Grimme’s dispersion correction method with the revised Tao-Mo semilocal functional quite accurately and effectively predict all the water properties including the water interaction with the nanostructured solids. It can serve as the benchmark tool of the water and water interaction on the surfaces instead of the expensive hybrid and wave function based methods. We are further using this method for molecular dynamics simulation and machine learning-based functional development.

We develop and implement new methodologies to understand and predict the novel properties of molecular and condensed matter systems. Our methodologies are implemented in various widely used codes such as VASP, FHI-AIMS, Q-Chem, NWChem, OCTOPUS, Quantum Espresso, deMon2k, PROFESS, and DFTpy. We implement several developed techniques such as semilocal, meta-GGA range-separated hybrids, RPA, and many-body perturbation techniques in widely used solid-state code VASP. Non-local functionals and dielectric-dependent hybrids for meta-GGA functionals in those codes are in the developing phase.