Assessment of Various Electronic Structure Methods for Characterizing Temporary Anion States: Application to the Ground State Anions of N₂, C₂H₂, C₂H₄, and C₆H₆

Abstract

The theoretical characterization of temporary anions is an especially challenging problem. In the present study we assess the performance of several electronic structure methods when used in conjunction with the stabilization method to characterize temporary anion states. The ground state anions of N2, C2H2, C2H4, and C6H6 are used as the test systems, with the most extensive testing being done for N2. For the (2)Πg anion state of N2(-) the ADC(2), EOM-MP2, and EOM-CCSD methods give values of the resonance parameters in excellent agreement with the results of prior high-level calculations. For the hydrocarbon systems, the EOM-MP2 method consistently provides excellent agreement with the EOM-CCSD results for the test systems, whereas the ADC(2) considerably underestimates the widths for ethylene and benzene. Several density functional theory (DFT) approaches are tested and, although none performs as well as the EOM-MP2 method, it is found that inclusion of Hartree-Fock exchange greatly improves the results. Of the DFT-based methods, time-dependent DFT with standard correlation functionals and use of Hartree-Fock exchange provides the best performance for N2(-) over the range of bond lengths considered and is also found to give reasonable values of the resonance parameters of the three hydrocarbon molecules.

Stabilizing potentials in bound state analytic continuation methods for electronic resonances in polyatomic molecules

“…The results at the CCSD level of theory agree fairly well with the EOM-EA-CCSD stabilization results presented in Ref. 49. The small differences are easily attributed to the slightly different level of theory and the different basis set.…”

“…However, the width computed with the type III-Coulomb method is consistently too large, and does not converge to the correct limit with increasing basis set size and level of theory. The performance of the type III method on method position width Stieltjes imaging 46 2.23 0.40 Schwinger variational + ADC(3) optical potential 47 2.534 0.536 3rd order decouplings of dilated electron propogator 48 2.11 0.18 EOM-EA-CCSD stabilization (aug-cc-pV5Z) 49 2.49 0.5 CAP EOM-EA-CCSD (1st order, aug-cc-pVQZ + 3s3p3d) 50 2 this particular problem is better than might be expected from the application to the model potential. This may be because, unlike in the case of the model potential, the width is almost an order of magnitude smaller than the position.…”

The Importance of Being Inconsistent

“…[PTHT15]. The importance of exact exchange has also been noticed for genuinely meta-stable anions [FDAB14], where the HOMO is positive.…”

Exploring the metastability and the pathways for polyanionic isomerization in the dianions and trianions of doubly- and triply-deprotonated benzene

“…However, based on a Coulomb model, the tunneling lifetimes for the electron loss in the investigated metastable molecular anions are found to be of the order of few femtoseconds rendering them difficult to be detectable. This work though provides significant insights into the chemical pathways of the reactions mediated through the proton-transfer processes in molecular anions; however, the results and discussions presented should be used only as an indicator for the future studies to be based on more appropriate theoretical methodologies for the treatment of molecular anions [2][3][4].…”

“…For this, the potential energy surfaces of the polyanionic species, in particular those of the doubly-deprotonated dianions, are successfully explored through an automated and systematic search performed using the global reaction route mapping method. The computations performed at the 1 3 99 Page 2 of 25 can be metastable, which are often categorized as temporary anions since their energy may lie above the ground state of the parent (neutral or ionic) species, at least at the geometry of the latter [2][3][4][5]. Such anions have negative electron affinity (EA); therefore, these species are shortlived due to the auto-detachment of the electron, resulting in the resonances.…”