Photoionization Observables from Multi-Reference Dyson Orbitals Coupled to B-Spline DFT and TD-DFT Continuum

Abstract

We present a theoretical model to compute the accurate photoionization dynamical parameters (cross-sections, asymmetry parameters and orbital, or cross-section, ratios) from Dyson orbitals obtained with the multi-state complete active space perturbation theory to the second order (MS-CASPT2) method. Our new implementation of Dyson orbitals in OpenMolcas takes advantage of the full Abelian symmetry point group and has the corrected normalization. The Dyson orbitals are coupled to an accurate description of the electronic continuum obtained with a multicentric B-spline basis at the DFT and TD-DFT levels. Two prototype diatomic molecules, i.e., CS and SiS, have been chosen due to their smallness, which hides important correlation effects. These effects manifest themselves in the appearance of well-characterized isolated satellite bands in the middle of the valence region. The rich satellite structures make CS and SiS the perfect candidates for a computational study based on our highly accurate MS-CASPT2/B-spline TD-DFT protocol.

Multi-Reference Approach to Normal and Resonant Auger Spectra Based on the One-Center Approximation

“…already available in OpenMolcas. 7,69,70 The spin-adapted Auger matrix elements R KI;qsr (also called two-particle Dyson matrix)…”

“…In most situations, the process can be treated accurately by first-order perturbation theory as the decay of a bound state into the underlying continuum. 7 The two most common types of Auger decay processes are normal Auger, exploited in normal Auger electron spectroscopy (herein indicated as AES), and resonant Auger, used in resonant Auger electron spectroscopy (RAES). [1][2][3] Similar (non-local) processes are inter-atomic Coulomb decay (ICD) 8,9 and electron transfer mediated decay (ETMD).…”

“…9,30 More general approaches rely on the use of a multicentric linear combination of atomic orbitals (LCAO) B-spline basis 31,32 with the correct asymptotic boundary conditions of the continuum, as obtained with the Bspline static-exchange Density Functional Theory (DFT) [33][34][35] and Time-Dependent Density Functional Theory (TD-DFT). 7,36 Theoretical approaches aiming at the calculation of molecular Auger decay rates reported in the literature rely on distinct approximations of the electronic continuum wave functions.…”

Multireference Approach to Normal and Resonant Auger Spectra Based on the One-Center Approximation

“…In most situations, the process can be treated accurately by first-order perturbation theory as the decay of a bound state into the underlying continuum. 7 The two most common types of Auger decay processes are normal Auger, exploited in normal Auger electron spectroscopy (herein indicated as AES), and resonant Auger, used in resonant Auger electron spectroscopy (RAES). 1 − 3 Similar (nonlocal) processes are interatomic Coulomb decay (ICD) 8 , 9 and electron transfer mediated decay (ETMD).…”

“…More general approaches rely on the use of a multicentric linear combination of atomic orbitals (LCAO) B-spline basis 32 , 33 with the correct asymptotic boundary conditions of the continuum, as obtained with the B-spline static-exchange density functional theory (DFT) 34 − 36 and time-dependent density functional theory (TD-DFT). 7 , 37 …”