Photoemission Spectra from the Extended Koopman’s Theorem

photo of Stefano Di Sabatino
Stefano Di Sabatino
University of Toulouse 3 - Paul Sabatier

The Extended Koopman’s Theorem (EKT) [1,2] provides a straightforward way to compute charged excitations from any level of theory.
In this work we get insight into the quality of removal/addition energies obtained using the EKT within reduced density matrix functional theory (RDMFT) [3]. 
Within this formulation the EKT reduces to a matrix diagonalization, whose ingredients are the one- and two-body reduced density matrices. We moreover show how to extend the EKT to the calculation of (approximate) spectral functions as well.
We present results both for model systems and realistic materials [4,5,6].

[1] M.M. Morrell, R.G. Parr,and M.Levy, J. Chem. Phys. 62, 62,549 (1975).
[2] O.W. Day, D. W. Smith, and R. C. Morrison, J. Chem. Phys. 62, 115 (1975)
[3] T. L. Gilbert, Phys. Rev. B 12, 2111 (1975).
[4] S. Di Sabatino, J. Koskelo, J. A. Berger, M. Caffarel, and P. Romaniello. Front. Chem.9:819 (2021).
[5] S. Di Sabatino, J. Koskelo, J. A. Berger, and P. Romaniello. Phys. Rev. Research,3, 013172 (2021).
[6] S. Di Sabatino, J. A. Berger, L. Reining, and P. Romaniello. Phys. Rev. B94, 155141 (2016).