Development of time-dependent GW for accurate investigations of chemical reactions

What is it about?

Ab initio Molecular dynamics (AIMD) is a simulation technique that incorporates the interdependence between instantaneous (or time-dependent) changes in the geometry and the electron energies. It is extensively used in deriving insights into chemical reactions among other applications. A chemical reaction comprises the formation of products from reactants and is always a dynamic process, making AIMD an essential tool for its study. Excitation of an electron to a higher energy level [in other words, moving from a ground state (lowest energy state) to an excited state] is usually involved in order to initiate a chemical reaction. A method known as real-time time-dependent density functional theory (RT-TDDFT) has been commonly used to study such chemical reactions, since it is computationally inexpensive (i.e., one does not require too much memory or computing power to obtain results). However, standard RT-TDDFT is not applicable to chemical reactions of reactants that are initially excited by photoabsorption. We have recently developed a dynamics methodology that computes energies using the GW approximation [which has been shown to provide superior estimates of band gaps and electron energies compared to those from density functional theory (DFT)], known as non-adiabatic excited-state time-dependent GW molecular dynamics (NA-ES-TDGW-MD, or TDGW in short). TDGW is the only method that can be used to study such chemical reaction dynamics accurately. Also, TDGW has the same computational cost as RT-TDDFT, which can be the main workhorse for dynamics in the future.

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Why is it important?

Our methodology time-dependent GW molecular dynamics (TDGW) is important since only this method is applicable to initially excited states unlike the standard workhorse for dynamics simulations, namely time-dependent density functional theory (TDDFT) and has the same computational cost as TDDFT. The inexpensive nature of TDGW can possibly be a method of choice to study excited-state chemical reactions very accurately, which can further our understanding of the world.