Electronic structure theory is the study of how electrons in a
crystal interacts with atomic vibrations, light, defects and other
external excitations via charges and energies that builds exciting
electronic, thermal, magnetic and optical properties. In 1965, a series
of two papers by Walter Kohn (Austrian born, American scientist) together with Pierre Hohenberg (French born American physicist) and Lu Jeu Sham (Chinese physicist) and later with John Pople (Bristish
chemist) demonstrated that the their ground-state energy functional
theory, the so-called “density functional theory” (sometimes also called
as “ab-initio formalism” or “first principles theory), is inevitable to
properly describe the electronic affairs inside crystal and attracted a
Noble prize in chemistry (1998), shared between Kohn and Pople.
In
early days, their theory was quite a challenge to solve because of lack
of obvious computational resources, thanks to the now commercially
available hardware accelerators and the high-speed data communicators,
their equations are now both mathematically enjoyable to solve and
develop.
In this group, we study the electronic correlations using
the most advanced linear response many body perturbation theory. Such
schemes are beyond the standard ground state energy functional theory
and arrows to a more advanced Hartree-Fock theory, Random-phase
approximation, self-consistent GW approximation and Bethe-Salpeter
equation. These challenging schemes are computational-costly practice,
but if mastered, can be done systematically and elegantly.