Performance of the DLPNO-CCSD and Recent DFT Methods in the Calculation of Isotropic and Dipolar Contributions to 14N Hyperfine Coupling Constants of Nitroxide Radicals

In the present study, the performance of a set of density functionals: BP86, PBE, OLYP, BEEF, PBEpow, TPSS, SCAN, PBEGXPBE, M06L, MN15L, B3LYP, PBE0, mPW1PW, B97, BHandHLYP, mPW1PW, HSE06, B98, TPSS0, PBE1KCIS, SCAN0, M06, M06-2X, MN15, CAM-B3LYP, ωB97x, B2PLYP, and the B3LYP/N07D and PBE/N07D schemes in the calculation of the 14N anisotropic hyperfine coupling (HFC) constants of a set of 23 nitroxide radicals is evaluated. The results are compared with those obtained with the DLPNO-CCSD method and experimental HFC values. Harmonic contribution to the 14N HFC vibrational correction was calculated at the revPBE0/def2-TZVPP level and included in the evaluation. With the vibrational correction, the DLPNO-CCSD method yielded HFC values in good agreement with the experiment (MAD = 0.3 G for the dipole-dipole contribution and MAD = 0.8 G for the contact coupling contribution). The best DFT results are obtained using the M06 functional with mean absolute deviation (MAD) = 0.2 G for the dipole-dipole contribution and MAD = 0.7 G for the contact coupling contribution. In general, vibrational correction significantly improved most DFT functionals' performance but did not change its overall ranking.

CAP-EOM-CCSD Method with Smooth Voronoi CAP for Metastable Electronic States in Molecular Clusters

The complex absorbing potential (CAP) approach offers a practical tool for characterization of energies and lifetimes of metastable electronic states, such as temporary anions and core ionized states. Here, we present an implementation of the smooth Voronoi CAP combined with equation-of-motion coupled cluster with single and double substitutions method for metastable states. The performance of the smooth Voronoi and a standard box CAPs is compared for different classes of systems: resonances in isolated molecules and in molecular clusters. The results of the benchmark calculations indicate that the choice of the CAP shape should be guided by the character of the metastable states. While Voronoi CAPs yield stable results in the case of a resonance localized on one molecule, their performance in the cases of states delocalized over two or more molecular species can deteriorate due to the CAP leaking into the vacuum region between the moieties. <br>

CAP-EOM-CCSD Method with Smooth Voronoi CAP for Metastable Electronic States in Molecular Clusters

The complex absorbing potential (CAP) approach offers a practical tool for characterization of energies and lifetimes of metastable electronic states, such as temporary anions and core ionized states. Here, we present an implementation of the smooth Voronoi CAP combined with equation-of-motion coupled cluster with single and double substitutions method for metastable states. The performance of the smooth Voronoi and a standard box CAPs is compared for different classes of systems: resonances in isolated molecules and in molecular clusters. The results of the benchmark calculations indicate that the choice of the CAP shape should be guided by the character of the metastable states. While Voronoi CAPs yield stable results in the case of a resonance localized on one molecule, their performance in the cases of states delocalized over two or more molecular species can deteriorate due to the CAP leaking into the vacuum region between the moieties. <br>

Dyson Orbitals within the fc-CVS-EOM-CCSD Framework

We report on the implementation and illustrative applications of Dyson orbitals within the recently proposed frozen-core (fc) core-valence separated (CVS) equation-of-motion (EOM) coupled-cluster singles and doubles (CCSD) method, which enables efficient and accurate characterization of core-ionized states. Dyson orbitals are reduced quantities that can be interpreted as correlated states of the ejected/attached electron.<br>Dyson orbitals enter the expressions of various experimental observables, such as photoionization cross sections; thus, they are necessary for modeling photoelectron spectra.<br>Here we discuss the simulations of X-ray photoelectron spectra (XPS) and propose an approach to simulate time-resolved (TR-)XPS for probing excited states. <br>As illustrative examples, we present the simulation of the XPS of the ground state of adenine and of TR-XPS of the excited states of uracil.