Excited-state potential energy curves from time-dependent density-functional theory: A cross section of formaldehyde's <SUP>1</SUP><TOGGLE>A</TOGGLE><INF>1</INF> manifold

This work reports the first density-functional theory (DFT) treatment of excited-state potential energy surfaces exhibiting avoided crossings. Time-dependent DFT (TD-DFT) results, using a recently proposed asymptotically corrected local density approximation functional, are compared with multireference doubles configuration interaction (MRD-CI) results for the ¹A<INF>1</INF> manifold of the CO stretching curves of planar formaldehyde. TD-DFT is found to reproduce the qualitative features essential for understanding the spectroscopy of this manifold, specifically the strong mixing of the ¹(π, π*) with Rydberg transitions and the resultant avoided crossings. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 933–941, 1998