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SUMMARY:Calculations of excited electronic states using density functional
 s - without introducing time-dependence - Professor Hannes Jónsson\, Univ
 ersity of Iceland
DTSTART:20250430T133000Z
DTEND:20250430T143000Z
UID:TALK224818@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:Calculations of excited electronic states are important in stu
 dies of various applications such as light harvesting\, photocatalysis and
  molecular motors. They are challenging as commonly used algorithms are de
 signed to converge on the ground state. As a result\, a time-dependent for
 mulation of density functional theory (DFT) is frequently used\, TD-DFT\, 
 especially within the linear response approximation. This approximate appr
 oach\, however\, has several limitations especially when significant charg
 e transfer occurs during the excitation and when states are close in energ
 y. Within configuration interaction (CI) theory\, it is evident that excit
 ed states correspond to saddle points on the electronic energy surface\, w
 ith the saddle point order increasing with the excitation level. While CI 
 calculations can be accelerated greatly by using neural networks [1]\, the
 y are much too computationally demanding for most problems of interest. DF
 T is used in most electronic structure calculations carried out today. By 
 using an algorithm for converging on saddle points on the electronic energ
 y surface of a density functional\, the orbitals can be optimised for the 
 excited state and provide higher energy solutions to the underlying Kohn-S
 ham equations [2\,3]. This gives more robust estimates of the excited stat
 es than TD-DFT while the computational effort is similar to that of a grou
 nd state calculation. \n>>>>>> Several applications of this approach with 
 commonly used density functionals will be presented\, as well as calculati
 ons using a self-interaction corrected functional that gives improved resu
 lts. In particular\, the various excited states of the ethylene molecule\,
  including the twisting of the C=C double bond\, the active element of sev
 eral molecular motors\, and high energy Rydberg states\, have been analyse
 d [4]. In a solid state application\, the various states relevant for the 
 optical preparation of a pure spin state in nitrogen/vacancy defect in dia
 mond\, a system used in various types of quantum technologies such as quan
 tum computing\, have been calculated. The results of these calculations ar
 e found to be in close agreement with computationally demanding\, high-lev
 el calculations as well as experiments [5].\n\n[1] Y. L. A. Schmerwitz\, L
 . Thirion\, G. Levi\, E.Ö. Jónsson\, P. Bilous\, H. Jónsson and P. Hans
 mann\, (submitted). \n[2] G. Levi\, A.V. Ivanov and H. Jónsson\, J. Chem.
  Theory Comput. 16\, 6968 (2020)\n[3] Y.L.A. Schmerwitz\, G. Levi and H. J
 ónsson\, J. Chem. Theory and Comput. 19\, 3634 (2023)\n[4] A.E. Sigurdars
 on\, Y.L.A. Schmerwitz\, D.K.V. Tveiten\, G. Levi and H. Jónsson\, J. Che
 m. Phys. 159\, 214109 (2023)\n[5] A.V. Ivanov\, Y.L.A. Schmerwitz\, G. Lev
 i and H. Jónsson\, SciPost Physics 15\, 009 (2023)\n
LOCATION:Unilever Lecture Theatre\, Yusuf Hamied Department of Chemistry
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