Benchmark relativistic delta-coupled-cluster calculations of K-edge core-ionization energies of third-row elements

Abstract

A benchmark computational study of K-edge core-ionization energies for third-row elements using relativistic delta-coupled-cluster (ΔCC) methods and a revised core-valence separation (CVS) scheme is reported. High-level relativistic (HLR) corrections beyond...

Accurate core excitation and ionization energies from a state-specific coupled-cluster singles and doubles approach

“…In a subsequent study, the same team found the relevance of going beyond S1 (CVS0 in their work) and using an equivalent to our S2 (CVS-ΔCCSD(T) in their work), they found excellent agreement with experiment as well. 107 The numbers they report on the third column of their Table 1, corresponding to their CVS-ΔCCSD(T) model with a TQ5-extrapolated cc-pCVXZ BSL, yield an MSE, MAE, and RMSE of 0.11, 0.13, and 0.17 eV for the subset of molecules common in both our data-sets (all of the ones presented here except Be and Ne,) using the experimental values we collected. Furthermore, they show that high-order relativistic effects ( i.e ., going beyond the exact two-component theory in its one-electron variant, or X2C-1e) are not relevant for second-row K-edge ionizations but they amount to −0.80 eV for Si, quickly increasing with the atomic number of the probed atom.…”

“…This treatment of the correlation involving the virtual core orbital is closely related to that 55 employed by Matthews in their study of core excitations 67 via the state-specific two-determinant Hilbert-space MR-CC, 82,83 and by Zhang et al for DCCSD(T) core ionizations. 107 S2 is pleasing in that, even though core substitutions are involved, they are all associated with configurations that retain a core occupancy of 1.…”

“…This treatment of the correlation involving the virtual core orbital is closely related to that 55 employed by Matthews in their study of core excitations 67 via the state-specific two-determinant Hilbert-space MR-CC, 82,83 and by Zhang et al for ΔCCSD(T) core ionizations. 107 S2 is pleasing in that, even though core substitutions are involved, they are all associated with configurations that retain a core occupancy of 1.As for S1, the CC de-excitation amplitudes are treated in a completely analogous way. We found that, in the case of the mixed singlets, allowing for the double substitution that generates the spin complement of the reference, a † h̄ a t̄ a † t a h with t being the target orbital, leads the CC iterations to converge towards the (lower energy) triplet excited state, resulting 〈 S 2 〉 values that deviate significantly from 1.…”

Relativistic Orbital-Optimized Density Functional Theory for Accurate Core-Level Spectroscopy

“…This analysis reveals that the spin-free X2C oneelectron Hamiltonian overbinds by 10.3 eV for Cu 2+ , which is comparable to the errors seen in Table 5. However, these contributions amount to 3.9 eV for Ti 4+ , indicating that they are very much relevant even for lighter elements (including the third period elements Si−Cl 122 ). It therefore appears that the good performance of OO-DFT/X2C in this regime is partly due to cancellation of errors between the missing relativistic contributions and the functional error from SCAN.…”

X-ray induced electron and ion fragmentation dynamics in IBr

“…To calculate the Br 1s and I 1s ionization energies of IBr, we began with the deltacoupled-cluster singles and doubles method augmented with a noniterative inclusion of triple excitations [∆ CCSD(T)] [21,22]. Scalar-relativistic effects were treated using the spin-free exact two-component theory in its one-electron variant (SFX2C-1e) [23,24].…”