Time-Dependent Density Functional Theory Beyond Kohn-Sham Slater Determinants

JOHANNA I. FUKS; SOEREN E. B. NIELSEN; MICHAEL RUGGENTHALER; NEEPA T. MAITRA

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2016 vol. 18 p. 20976 - 20985

1463-9076

When running time-dependent density functional theory (TDDFT) calculations for real-time simulations of non-equilibrium dynamics, the user has a choice of initial Kohn-Sham state, and typically aSlater determinant is used. We explore the impact of this choice on the exchange-correlation potential when the physical system begins in a 50:50 superposition of the ground and first-excited state of thesystem. We investigate the possibility of judiciously choosing a Kohn-Sham initial state that minimizes errors when adiabatic functionals are used. We find that if the Kohn-Sham state is chosen tohave a configuration matching the one that dominates the interacting state, this can be achieved for afinite time duration for some but not all such choices. When the Kohn-Sham system does not beginin a Slater determinant, we further argue that the conventional splitting of the exchange-correlationpotential into exchange and correlation parts has limited value, and instead propose a decomposition into a ?single-particle? contribution that we denote vXCS, and a remainder. The single-particlecontribution can be readily computed as an explicit orbital-functional, reduces to exchange in theSlater determinant case, and offers an alternative to the adiabatic approximation as a starting pointfor TDDFT approximations.