Exploring the accuracy of a low scaling similarity transformed equation of motion method for vertical excitation energies.

Research paper by Achintya Kumar AK Dutta, Marcel M Nooijen, Frank F Neese, Robert R Izsak

Indexed on: 06 Dec '17Published on: 06 Dec '17Published in: Journal of Chemical Theory and Computation


The newly developed back transformed pair natural orbital based similarity transformed equation of motion (bt-STEOM) method at the coupled cluster singles anddoubles level (CCSD) is combined with an appropriate modification of our earlier active space selection scheme for STEOM. The resulting method is benchmarked for valence, Rydberg and charge transfer excited states of Thiel's test set and other test systems. The bt-PNO-STEOM-CCSD method gives very similar results to canonical STEOM-CCSD for both singlet and triplet excited states. It performs in a balanced manner for all these types of excited states, while the EOM-CCSD method performs especially well for Rydberg excited states and the CC2 method excels at obtaining accurate results for valence excited states. Both EOM-CCSD and CC2 perform worse than bt-PNO-STEOM-CCSD for charge transfer states for the test cases studied.