Tempel, DavidAspuru-Guzik, Alan2012-03-232011Tempel, David Gabriel, and Alán Aspuru-Guzik. 2011. Relaxation and dephasing in open quantum systems time-dependent density functional theory: Properties of exact functionals from an exactly-solvable model system. Chemical Physics 391(1): 130–142.0301-0104http://nrs.harvard.edu/urn-3:HUL.InstRepos:8438167The dissipative dynamics of many-electron systems interacting with a thermal environment has remained a long-standing challenge within time-dependent density functional theory (TDDFT). Recently, the formal foundations of open quantum systems time-dependent density functional theory (OQS-TDDFT) within the master equation approach were established. It was proven that the exact time-dependent density of a many-electron open quantum system evolving under a master equation can be reproduced with a closed (unitarily evolving) and non-interacting Kohn–Sham system. This potentially offers a great advantage over previous approaches to OQS-TDDFT, since with suitable functionals one could obtain the dissipative open-systems dynamics by simply propagating a set of Kohn–Sham orbitals as in usual TDDFT. However, the properties and exact conditions of such open-systems functionals are largely unknown. In the present article, we examine a simple and exactly-solvable model open quantum system: one electron in a harmonic well evolving under the Lindblad master equation. We examine two different representitive limits of the Lindblad equation (relaxation and pure dephasing) and are able to deduce a number of properties of the exact OQS-TDDFT functional. Challenges associated with developing approximate functionals for many-electron open quantum systems are also discussed.en-UStime-dependent density functional theoryopen quantum systemsrelaxationdecoherenceLindblad master equationchemical physicsquantum physicsother condensed matterJournal Article2012-03-2310.1016/j.chemphys.2011.03.014