CAREER: Electron correlation and optical spectra with a nonlocal energy-optimized (NEO) kernel

Temple University, Philadelphia PA

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports theoretical and computational research and education aimed to improve theoretical and computational methods for computing properties of molecules and materials. The PI aims to develop a computationally efficient and usefully accurate correction to present computational methods of calculating the properties of materials starting from constituent atoms based on the density-functional-theory. The approach appeals to an approximation within another theoretical formulation of the quantum mechanical description of many interacting particles that would be computationally very expensive to evaluate. The approximation is known as the random phase approximation. The PI's method should have a higher accuracy and be computationally inexpensive compared to many currently existing methods. It should also enable higher accuracy calculations of systems in which the configuration of electrons leads to a higher energy than the lowest or ground state energy of the system. The operation of a solar cell provides examples which the research will explore. The PI will test her method through calculations of materials properties and comparisons with results from other theoretical and computational methods, and experiments. . This award supports an educational activity focused on graduate, undergraduate and high-school students. A thrust of this activity is linked to the TUTeach program which trains high-school teachers. The students in this program are physics majors, who will work as learning assistants for the PI and learn about the PI's research. These students are also outreach ambassadors in the high schools. TUTeach students will work with the PI to deliver computational physics lectures to high-school students. The PI will also mentor students within the local provost's research-experiences-for-undergraduates program. Another significant component of the PI's education program is to develop a new active-learning-based Computational Materials Physics course. TECHNICAL SUMMARY This CAREER award supports theoretical and computational research and education to develop more accurate density functional theory-based calculations of ground-state energies and excited state properties of materials. The PI has two goals through this project: (1) To develop a computationally efficient correction to the ground-state correlation energy of the random phase approximation. Without a correction, the random phase approximation would not be accurate enough to become a benchmark in chemistry and materials science. Some of the currently existing corrections are accurate, but the price is a high computational cost. (2) To make the computationally efficient time-dependent density functional theory competitive in accuracy with more complex quantum many-body techniques. Time-dependent density functional theory is an extension of density functional theory to time-dependent potentials. Time-dependent density functional theory has become a very popular tool to compute excitation energies. It is computationally efficient, but its accuracy is moderate compared to quantum many-body Green's function-based methods. The most commonly used adiabatic local density kernel misses excitonic effects. The PI will further develop a nonlocal energy-optimized kernel model that is computationally efficient and can capture these effects. Both for ground and excited states the same nonlocal exchange-correlation kernel is to be added to the Coulomb electron-electron interaction kernel in the frequency-dependent linear response function of the ground state. The nonlocal energy-optimized kernel will be applied to molecules and materials. The kernel correction will be tested and applied to many ground-state properties, such as atomization energies, cohesive energies, structural phase transitions, clusters and adsorption problems. The kernel correction to time-dependent density functional theory will be applied to excitation energies including those in semiconductors with a particular focus on photovoltaic materials for solar cell applications. This award supports an educational activity focused on graduate, undergraduate and high-school students. A thrust of this activity is linked to the TUTeach program which trains high-school teachers. The students in this program are physics majors, who will work as learning assistants for the PI and learn about the PI's research. These students are also outreach ambassadors in the high schools. TUTeach students will work with the PI to deliver computational physics lectures to high-school students. The PI will also mentor students within the local provost's research-experiences-for-undergraduates program. Another significant component of the PI's education program is to develop a new active-learning-based Computational Materials Physics course.