TY - JOUR
T1 - Localized and Delocalized States of a Diamine Cation
T2 - Resolution of a Controversy
AU - Gałyńska, Marta
AU - Ásgeirsson, Vilhjálmur
AU - Jónsson, Hannes
AU - Bjornsson, Ragnar
N1 - Funding Information: M.G. acknowledges a postdoctoral fellowship from the University of Iceland Research Fund. This work was supported by the Icelandic Research Fund. R.B. acknowledges the Max Planck Society for funding. The computations were performed on resources provided by the Icelandic Research High Performance Computing Centre (IRHPC) at the University of Iceland. Publisher Copyright: © 2021 The Authors. Published by American Chemical Society.
PY - 2021/1/26
Y1 - 2021/1/26
N2 - Recent Rydberg spectroscopy measurements of a diamine molecule, N,N′-dimethylpiperazine (DMP), indicate the existence of a localized electronic state as well as a delocalized electronic state. This implies that the cation, DMP+, can similarly have its positive charge either localized on one of the N atoms or delocalized over both. This interpretation of the experiments has, however, been questioned based on coupled cluster calculations. In this article, results of high-level multireference configuration interaction calculations are presented where a localized state of DMP+ is indeed found to be present with an energy barrier separating it from the delocalized state. The energy difference between the two states is in excellent agreement with the experimental estimate. The results presented here, therefore, support the original interpretation of the experiments and illustrate a rare shortcoming of CCSD(T), the "gold standard"of quantum chemistry. These results have implications for the development of density functionals, as most functionals fail to produce the localized state.
AB - Recent Rydberg spectroscopy measurements of a diamine molecule, N,N′-dimethylpiperazine (DMP), indicate the existence of a localized electronic state as well as a delocalized electronic state. This implies that the cation, DMP+, can similarly have its positive charge either localized on one of the N atoms or delocalized over both. This interpretation of the experiments has, however, been questioned based on coupled cluster calculations. In this article, results of high-level multireference configuration interaction calculations are presented where a localized state of DMP+ is indeed found to be present with an energy barrier separating it from the delocalized state. The energy difference between the two states is in excellent agreement with the experimental estimate. The results presented here, therefore, support the original interpretation of the experiments and illustrate a rare shortcoming of CCSD(T), the "gold standard"of quantum chemistry. These results have implications for the development of density functionals, as most functionals fail to produce the localized state.
UR - https://www.scopus.com/pages/publications/85100826548
U2 - 10.1021/acs.jpclett.0c03651
DO - 10.1021/acs.jpclett.0c03651
M3 - Article
C2 - 33497225
SN - 1948-7185
VL - 12
SP - 1250
EP - 1255
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 4
ER -