Investigation of the Impact of Different Terms in the Second Order Hamiltonian on Excitation Energies of Valence and Rydberg States

A. Tajti, Péter G. Szalay

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Describing electronically excited states of molecules accurately poses a challenging problem for theoretical methods. Popular second order techniques like Linear Response CC2 (CC2-LR), Partitioned Equation-of-Motion MBPT(2) (P-EOM-MBPT(2)), or Equation-of-Motion CCSD(2) (EOM-CCSD(2)) often produce results that are controversial and are ill-balanced with their accuracy on valence and Rydberg type states. In this study, we connect the theory of these methods and, to investigate the origin of their different behavior, establish a series of intermediate variants. The accuracy of these on excitation energies of singlet valence and Rydberg electronic states is benchmarked on a large sample against high-accuracy Linear Response CC3 references. The results reveal the role of individual terms of the second order similarity transformed Hamiltonian, and the reason for the bad performance of CC2-LR in the description of Rydberg states. We also clarify the importance of the T1 transformation employed in the CC2 procedure, which is found to be very small for vertical excitation energies.

Original languageEnglish
Pages (from-to)5477-5482
Number of pages6
JournalJournal of Chemical Theory and Computation
Volume12
Issue number11
DOIs
Publication statusPublished - Nov 8 2016

ASJC Scopus subject areas

  • Computer Science Applications
  • Physical and Theoretical Chemistry

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