Development of Theoretical Tools for Modeling Core and Valence Spectroscopies and their Applications to Species of Atmospheric Interest
Résumé
Achieving the ionization potentials of core electrons is becoming easier with the advances in X-ray spectroscopy, both the high energies become accessible and the precision improves [1]. The consideration of relativistic effects is necessary [2], so we are working to obtain these energies using 4-component Hamiltonians (Dirac-Coulomb / Dirac-Coulomb-Gaunt) by Equation of Motion Coupled Cluster (EOM-CCSD) implemented in the DIRAC code [3]. This method has many advantages both in terms of its precision and its predictions [4]. The size of the matrix (EOM) and the computational cost in N , real computational limitations, can be outwitted by the use of approximations, namely when calculating the reference wave
function by neglecting some amplitudes T of the CC calculation (Frozen-Core (FC) [3]), or by limiting its size by the use of projectors (Core Valence Separation (CVS) [5,6] / No Double Excitation in Core (ND) [3]). This work shows the interest of applying these approximations and of testing their different degrees of precision in order to obtain the ionization energies of the core electrons. The studied systems are notably the highly relativistic core electrons in Xe, and {X-; HX (with X in {Cl, Br, I}) which have atmospheric interests.
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[1] Boudjemia N. et al., Phys. Chem. Chem. Phys. 21, 5448, (2019)
[2] Fleig T. et al., Chem. Phys. 2 395 (2012); Saue T. et al., Chem. Phys. Chem. 12 3077, (2011)
[3] Saue T. et al, J. Chem. Phys. 152; 204104, (2020)
[4] Shee A. et al., J. Chem. Phys. 149, 174113, (2018)
[5] Coriani S. et al., J. Chem. Phys 143, 181103, (2015)
[6] Dreuw, A. et al., WIREs Comp. Mol S, 5:82-95, (2015)
[7] Southworth S. H. et al., J. Chem. Phys, 142, 224302, (2015)
[8] Oura M. et al. New J. Phys 21, 043015, (2019)
[9] Sikkema J. et al.,J. Chem. Phys. 131, 124116 (2009)