QUESTDB: A database of highly accurate excitation energies
Date:
The accurate modelling of excited-state energies and properties with ab initio quantum chemistry methods is a clear ambition of the electronic structure theory community. One particularly interesting and challenging aspect of molecular excited states is their variety and the large panel of methods that have been created to compute their vertical transitions energies. To ease comparisons between this zoo of theoretical models, in the last few years, we have created a large set of highly accurate vertical excitation energies (currently more than 500) of various natures (π → π, n → π, double excitation, Rydberg, singlet, doublet, triplet, etc.) in small- and medium-sized molecules. These reference values have been obtained using an incremental strategy which consists in combining high-order coupled cluster and selected configuration interaction calculations using increasingly large basis sets in order to reach high accuracy. Thank to this systematic strategy, we have been able to produce theoretical best estimates (TBEs) with the aug-cc-pVTZ basis set for each of these transitions, as well as basis set corrected TBEs for some of them. The TBEs/aug-cc-pVTZ have been employed to benchmark a large number of (lower-order) wave function methods. In order to gather the huge amount of data produced during the QUEST project, we have created a website (https://lcpq.github.io/QUESTDB_website) where one can easily test and compare the accuracy of a given method with respect to various variables. A live demonstration will be given during the present talk.