Probing Dyson orbitals with Green’s Function theory and Electron Momentum Spectroscopy

High resolution electron momentum spectroscopy of the valence orbitals of water

“…The overlap of the ion and neutral wavefunctions in Eq. (2) is referred to as a Dyson orbital [5][6][7][8][9][10][11][12]. Dyson orbitals are straightforwardly obtained from CI [31] or Green's Function (GF) calculations [9][10][11]54].…”

“…In our work, these calculations are based on CAS reference wave functions employing an active space constructed by distributing the 7 valence electrons over 11 orbitals, among which there are 6, 3, and 2 orbitals with a 1 , b 1 and b 2 symmetry labels, respectively [CAS (7,11)]. The same wavefunction was used to carry our further multi-reference calculations in conjunction with second-and third-order Rayleigh Schrödinger perturbation theory (MR-RSPT2; MR-RSPT3 [77]).…”

“…However, the available EMS spectrometers still badly need improvements with regards to energy and momentum resolution for probing on more quantitative grounds the outcome of the dynamical correlation and relaxation effects induced by (e, 2e) ionization processes on the effective shape and spread of the orbitals involved in these processes. In an exact theory of ionization at the limit of high kinetic energies for the impinging electrons, the measured electron momentum distributions relate to Dyson orbitals [5][6][7][8][9][10][11][12], measuring partial overlaps between the neutral ground state and the corresponding cationic states of the target.…”

Vibrational effects on valence electron momentum distributions of CH2F2

“…Indeed, for this molecule, a significant difference between experiment and theory has been reported for a valence orbital, 2b 1 , which has the CH-bonding character. 28,38,39 In the present work, electron momentum profiles of the valence orbitals of CH 2 F 2 have been measured experimentally with high statistical accuracy by using one of our multi-channel EMS spectrometer. 40 Theoretically, their electron momentum profiles have been calculated while effects of all the vibrational modes being involved.…”

Electron momentum spectroscopy of metal carbonyls: a reinvestigation of the role of nuclear dynamics

“…A further and most useful approximation is the target Kohn-Sham approximation [12], which consists in substituting Dyson orbitals by the relevant Kohn-Sham orbitals, along with ad hoc or calculated spectroscopic pole strengths, in order to account for the flux of ionization intensity toward shake-up [13] and valence correlation bands [14] at higher electron binding energies. In many cases, (rescaled) Kohn-Sham orbitals are empirically known to be excellent approximations to Dyson orbitals [15,16]. In practice, however, the interpretation of EMS experiments is subject to numerous complications such as: overlap effects in overcrowed ionization bands [17,18], conformational mobility [19][20][21] and (thermally induced) nuclear dynamics in the electronic initial (neutral) ground state [22], shake-up processes due to electronic configuration interactions in the final ionized state [23][24][25][26], distorted wave and post-collision (e.g., rescattering) effects [27][28][29][30][31][32][33], and possibly ultra-fast nuclear dynamics in the final ionized state, in the form of bond breaking [22] or Coulomb explosion processes [34][35][36], as well as Jahn-Teller distortions [37] in the final ionized state.…”