My current research project is mainly on the particle-particle random phase approximation (pp-RPA), a theoretical method that is based on but also beyond the widely used density functional approximations. The pp-RPA actually has been a textbook method for treating correlation in nuclear physics for a long time, but in the recent years we introduced it to atomic and molecular systems. We also successfully combined it with density functional approximations besides the traditional Hartree-Fock approximation.
What I work on most is to apply the pp-RPA to electronic excitation problems. These problems include challenging double excitation, charge transfer excitation, Rydberg excitation, and diradical problems. The calculation usually starts from a two-electron deficient system and then recovers a series of neutral states by adding two electrons back to the system. Although it intrinsically misses those excitations from below the highest occupied molecular orbital, it often can solve above challenging excitation problems that cannot be well described by the more widely-used adiabatic time-dependent density functional theory (TDDFT).
The pp-RPA is in nature a theoretical counterpart of TDDFT and potentially can be quite useful. We hope it can some day become another powerful tool for solving excited states problems.