Computation of Molecular Electron Affinities Using an Ensemble Density Functional Theory Method

Advancing electrocatalytic reactions through mapping key intermediates to active sites via descriptors

Descriptors play a crucial role in electrocatalysis as they can provide valuable insights into the electrochemical performance of energy conversion and storage processes. They allow for the understanding of different catalytic activities and enable the prediction of better catalysts without relying on the time-consuming trial-and-error approaches. Hence, this comprehensive review focuses on highlighting the significant advancements in commonly used descriptors for critical electrocatalytic reactions. First, the fundamental reaction processes and key intermediates involved in several electrocatalytic reactions are summarized. Subsequently, three types of descriptors are classified and introduced based on different reactions and catalysts. These include d-band center descriptors, readily accessible intrinsic property descriptors, and spin-related descriptors, all of which contribute to a profound understanding of catalytic behavior. Furthermore, multi-type descriptors that collectively determine the catalytic performance are also summarized. Finally, we discuss the future of descriptors, envisioning their potential to integrate multiple factors, broaden application scopes, and synergize with artificial intelligence for more efficient catalyst design and discovery.

A comparable DFT study on reaction of CHCl•- with O3 and S2O

CONTEXT

In this discussion, we began building two model, S₂O + CHCl^•- and O₃ + CHCl^•-, using DFT-BHandHLYP method, to study their reactions mechanisms on singlet PES. For this purpose, we hope to explore the effects of the difference between sulfur and oxygen atoms on the CHCl^•- anion. Experimentalists and computer scientists may utilize the collected data to generate a wide range of hypotheses for experimental phenomena and predictions, allowing them to realize their full potential.

METHODS

The ion-molecule reaction mechanism of CHCl^•- with S₂O and O₃ was studied using the DFT-BHandHLYP level of theory with the aug-cc-pVDZ basis set. Our theoretical findings show that Path 6 is the favored reaction pathway for CHCl^•- + O₃ reaction as identified by the O-abstraction reaction pattern. Comparing to the direct H- and Cl-abstraction mechanisms, the reaction (CHCl^•- + S₂O) prefers the intramolecular S_N2 reaction pattern. Moreover, the calculated results demonstrated that the CHCl^•- + S₂O reaction is thermodynamically more favorable than the CHCl^•- + O₃ reaction, which is kinetically more advantageous. As a result, if the required reaction condition in the atmospheric process is met, the O₃ reaction will happen more effectively. In terms of kinetics and thermodynamics viewpoints, the CHCl^•- anion was very effective in eliminating S₂O and O₃.

Ensemble Density Functional Theory of Neutral and Charged Excitations : Exact Formulations, Standard Approximations, and Open Questions

Recent progress in the field of (time-independent) ensemble density-functional theory (DFT) for excited states are reviewed. Both Gross-Oliveira-Kohn (GOK) and N-centered ensemble formalisms, which are mathematically very similar and allow for an in-principle-exact description of neutral and charged electronic excitations, respectively, are discussed. Key exact results, for example, the equivalence between the infamous derivative discontinuity problem and the description of weight dependencies in the ensemble exchange-correlation density functional, are highlighted. The variational evaluation of orbital-dependent ensemble Hartree-exchange (Hx) energies is discussed in detail. We show in passing that state-averaging individual exact Hx energies can lead to severe (although solvable) v-representability issues. Finally, we explore the possibility of using the concept of density-driven correlation, which has been introduced recently and does not exist in regular ground-state DFT, for improving state-of-the-art correlation density-functional approximations for ensembles. The present review reflects the efforts of a growing community to turn ensemble DFT into a rigorous and reliable low-cost computational method for excited states. We hope that, in the near future, this contribution will stimulate new formal and practical developments in the field.

State-Of-The-Art Computations of Vertical Electron Affinities with the Extended Koopmans' Theorem Integrated with the CCSD(T) Method

Accurate computation of electron affinities (EAs), within 0.10 eV, is one of the most challenging problems in modern computational quantum chemistry. The extended Koopmans' theorem (EKT) enables direct computations of electron affinities (EAs) from any level of the theory. In this research, the EKT approach based on the coupled-cluster singles and doubles with perturbative triples [CCSD(T)] method is applied to computations of EAs for the first time. For efficiency, the density-fitting (DF) technique is used for two-electron integrals. Further, the EKT-CCSD(T) method is applied to three test sets of atoms and closed- and open-shell molecules, denoted A16, C10, and O33, respectively, for comparison with the experimental electron affinities. For the A16, C10, and O33 sets, the EKT-CCSD(T) approach, along with the aug-cc-pV5Z basis set, provide mean absolute errors (MAEs) of 0.05, 0.08, and 0.09 eV, respectively. Hence, our results demonstrate that high-accuracy computations of EAs can be achieved with the EKT-CCSD(T) approach. Further, when the EKT-CCSD(T) approach is not computationally affordable, the EKT-MP2.5, EKT-LCCD, and EKT-CCSD methods can be considered, and their results are also reasonably accurate. The huge advantage of the EKT method for the computation of IPs is that it comes for free in an analytic gradient computation. Hence, one needs neither separate computations for neutral and ionic species, as in the case of common approaches, nor additional efforts to obtain IPs, as in the case of equation-of-motion approaches. Overall, we believe that the present research may open new avenues in EA computations.

Exploring Dyson's Orbitals and Their Electron Binding Energies for Conceptualizing Excited States from Response Methodology

The molecular orbital (MO) concept is a useful tool, which relates the molecular ground-state energy with the energies (and occupations) of the individual orbitals. However, analysis of the excited states from linear response computations is performed in terms of the initial state MOs or some other forms of orbitals, e.g., natural or natural transition orbitals. Because these orbitals lack the respective energies, they do not allow developing a consistent orbital picture of the excited states. Herein, we argue that Dyson's orbitals enable description of the response states compatible with the concepts of molecular orbital theory. The Dyson orbitals and their energies obtained by mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) for the response ground state are remarkably similar to the canonical MOs obtained by the usual DFT calculation. For excited states, the Dyson orbitals provide a chemically sensible picture of the electronic transitions, thus bridging the chasm between orbital theory and response computations.

Description of Sudden Polarization in the Excited Electronic States with an Ensemble Density Functional Theory Method

Sudden polarization (SP) is one of the manifestations of electron transfer in the electronically excited states of molecules. Proposed initially to explain the unusual reactivity of photoexcited olefins, SP often occurs in the excited states of molecules possessing strongly correlated diradical ground state. Theoretical description of SP involves mixing between the singly excited and the doubly excited zwitterionic states, which makes it inaccessible with the use of the popular linear-response time-dependent density functional theory methods. In this work, an extended variant of the state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS, or SSR) method is applied to study SP in a number of organic diradical systems. To this end, the analytical derivative formalism is derived and implemented for the SSR(3,2) method (see the main text for explanation of the acronym), which enables the automatic geometry optimization and obtains the relaxed density matrices as well as the electron binding energies and respective Dyson's orbitals. Application of the new method to SP in the lowest singlet excited state of ethylene agrees with the results obtained previously with the use of multireference methods of wavefunction theory. A number of interesting manifestations of SP are observed, such as the charge transfer in photoexcited tetramethyleneethene (TME) diradical mediated by the vibrational motion and conductivity switching in the excited state of a donor-acceptor dyad placed in an external electric field.

Cu2+-modified MOF as laccase-mimicking material for colorimetric determination and discrimination of phenolic compounds with 4-aminoantipyrine

Based on the laccase-mimicking activity of Cu²⁺-modified University of Oslo (UiO) metal-organic framework (UiO-67-Cu²⁺), we developed a colorimetric sensor array for distinguishing a series of phenols with different number and position of substituted hydroxyl group (-OH) and different substituent group on the benzene ring, including phenol, catechol, quinol, resorcinol, pyrogallol, phloroglucinol, o-chlorophenol, o-aminophenol, and o-nitrophenol. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of phenolic compounds were obtained by theoretical calculation. The results show that the lower the LUMO energy level, the easier the chromogenic reaction occurs. The UiO-67-Cu²⁺-catalyzed phenol chromogenic reaction showed a good linearity in the range from 0.1 to 200 μM with limit of detection approximately 61 nM. Through the detection of phenol in tap water and river water, the recovery rate and RSD (n = 3) were calculated as 94.1~103% and 1.0~3.3, respectively, showing good recovery, reliable results, and outstanding stability. Therefore, the proposed colorimetric sensor array will have a great potential for the detection of phenols in the environment. Schematic presentation of a simple and sensitive colorimetric strategy based on the laccase-mimicking activity of Cu²⁺-modified UiO-type metal-organic framework (MOFs, Uio-67-Cu²⁺) to distinguish phenols with analogous structures.

Signatures of Conical Intersection Dynamics in the Time-Resolved Photoelectron Spectrum of Furan: Theoretical Modeling with an Ensemble Density Functional Theory Method

The non-adiabatic dynamics of furan excited in the ππ* state (S2 in the Franck-Condon geometry) was studied using non-adiabatic molecular dynamics simulations in connection with an ensemble density functional method. The time-resolved photoelectron spectra were theoretically simulated in a wide range of electron binding energies that covered the valence as well as the core electrons. The dynamics of the decay (rise) of the photoelectron signal were compared with the excited-state population dynamics. It was observed that the photoelectron signal decay parameters at certain electron binding energies displayed a good correlation with the events occurring during the excited-state dynamics. Thus, the time profile of the photoelectron intensity of the K-shell electrons of oxygen (decay constant of 34 ± 3 fs) showed a reasonable correlation with the time of passage through conical intersections with the ground state (47 ± 2 fs). The ground-state recovery constant of the photoelectron signal (121 ± 30 fs) was in good agreement with the theoretically obtained excited-state lifetime (93 ± 9 fs), as well as with the experimentally estimated recovery time constant (ca. 110 fs). Hence, it is proposed to complement the traditional TRPES observations with the trXPS (or trNEXAFS) measurements to obtain more reliable estimates of the most mechanistically important events during the excited-state dynamics.