Research Projects

In the last few decades, a new generation of materials are bringing drastic changes in different fields of science and technology. These materials are often referred to as “quantum materials” as properties of these materials can only be explained using quantum mechanics. This category of functional materials includes molecular electronics, bioelectronics, organic solar cells, qubits, quantum sensors, quantum dots and many other materials. Quantum chemical electronic structure methods have contributed significantly in atomistic understanding of many properties of these systems. In recent years, computational chemistry has started to play a major role in guiding the discovery of new quantum materials. Kohn-Sham density functional theory (KS-DFT) has been a major driving force behind the success of computational methods in materials discovery. In spite of its remarkable success, accuracy of KS-DFT is still questionable for strongly correlated systems or systems for which the wave function cannot be represented properly with a single Slater determinant. Systems with unpaired electrons in the ground or excited states often fall in the category of strongly correlated systems. Both organic and inorganic functional materials may fall in this category. Organic molecules with extended π-conjugation often have open-shell singlet ground state, low-lying excited states or multiexcitonic states. Such π-conjugated systems have application as solar cell materials, light emitting diodes, organic qubits or organic magnets. Inorganic molecules with unpaired d or f electrons can be used as molecular magnets and qubits. Unlike KS-DFT, multiconfiguration methods can represent the wave function of an electronic state as a linear combination of multiple Slater determinants. However, multireference perturbation theory (MRPT) needs to be applied using multireference wave function to obtain quantitatively accurate results. Application of MRPT is limited due to its high computational cost and memory requirements. One way to reduce the computational cost would be to eliminate MRPT step with a DFT approach. With this goal, in this project, a new multiconfiguration density functional theory (MC-DFT) will be developed. In this method, a multiconfiguration wave function can be obtained from any method that can generate multiconfiguration wave function. Then the wave function will be used to compute kinetic energy, electron-nuclear interaction energy and classical Coulomb energy. Missing exchange and correlation energies will be computed using a new type of exchange-correlation functional called on-top pair-density functional. Developed method will provide accuracy similar to MRPT with the same computational cost as multireference wave function method as the cost of the DFT calculation will be negligible. MC-DFT will provide a new computational approach to model ground and excited states of quantum materials and discover new molecular structures.