Bonn 2000 – scientific programme
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MO: Molekülphysik
MO 9: Theorie: Dynamik und Struktur
MO 9.7: Talk
Tuesday, April 4, 2000, 18:00–18:15, HV IV
Potential Energy Surfaces of Excited States from Time-Dependent Density-Functional Theory — •Xavier Gonze1,2, Martin Fuchs1,2, Thorsten Klüner2, and Matthias Scheffler2 — 1Department of Materials Sciences, UCL, Louvain-la-Neuve, Belgium — 2Fritz-Haber-Institut der MPG, Berlin, Germany
Density-functional theory (DFT) has been very successful in the analysis of interacting-electron ground states. Many efforts have also been devoted to DFT-based schemes for excited states. Recently, the feasibility of excitation-energy computations relying on time-dependent density-functional theory (TD-DFT) has been demonstrated for atoms, small molecules, and clusters. Here we apply TD-DFT to compute excited state potential-energy surfaces. For the (HeH)+ system, we investigate the ground state as well as the lower-lying singlet and triplet states, for a series of internuclear distances. We work both in the local-density approximation (TD-LDA) and in the exchange-only optimized effective potential approximation (TD-xOEP). For this system, a comparison with configuration interaction (CI) data shows that TD-LDA is insufficient. TD-xOEP gives much better results, especially for the position of the avoided crossings of the different curves. The good approximation to the true exchange-correlation potential provided by the xOEP partly explains this. Surprisingly, for some of the singlet excited states, the straight xOEP Kohn-Sham eigenvalue differences, which form the starting point of TD-xOEP, agree even better with the CI data. We also compute excited state energies within the ΔSCF approach, using the LDA. In general, TD-xOEP and ΔSCF results show comparable accuracy.