Also included is a Feshbach-Fano analysis of the relevance of virtual- valence orbitals to the appearance of single-channel resonances in molecular photoionization cross sections.Įxploring the Nature of the H Bond. FEMO orbital energies and resonance positions are found to be in good agreement with previous theoretical and experimental results. The results of molecular-orbital computations are presented in three-dimensional diagrams, which are shown to be similar to the wave functions of a particle in a cylindrical well, confirming the validity of free-electron molecular-orbital (FEMO) approximations for modeling the potential along the symmetry axis. The relationship between the interatomic distance and the positions of valence-shell and K-shell sigma(asterisk) photoionization resonances is investigated theoretically for the molecules C2, F2, N2, O2, CO, NO, C2H2, C2H4, C2H6, HCN, H2CO, N20, CO2, and C2N2. ? 1986.Ĭorrelation of molecular valence- and K-shell photoionization resonances with bond lengths In agreement with Zener's double exchange model, FeFe bonding is found to stabilize ferromagnetic coupling between Fe2+ and Fe3+ cations. The cluster calculations show that electron hopping and optical intervalence charge-transger result from weak FeFe bonding across shared edges of FeO6 coordination polyhedra. Boemer, ChristinaĬluster molecular orbital description of the electronic structures of mixed- valence iron oxides and silicatesĪ molecular orbital description, based on spin-unrestricted X?-scattered wave calculations, is given for the electronic structures of mixed valence iron oxides and silicates. Vtc-XES offers particular insight into the molecular orbitalsmoreÂ Â» directly involved in the light-driven dynamics a change in the metal-ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations and more subtle features at the highest energies reflect changes in the frontier orbital populations.Â«Â less A picosecond-time-resolved measurement of the complete Is X-ray emission spectrum captures the transient photoinduced changes and includes the weak valence-to-core (vtc) emission lines that correspond to transitions from occupied valence orbitals to the nascent core-hole. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making it a powerful technique for molecular studies in a wide variety of environments. Here we probe the dynamics of valence electrons in photoexcited 2+ in solution to gain deeper insight into the Fe-ligand bond changes. Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy In these cases the technique makes MR calculations easier to execute, easier to reproduce by any user, and simplifies the determination of the appropriate size of the active space required for accurate results. While the described AVAS technique is not a universal solution to the active space problem, its premises are fulfilled in many application scenarios of transition-metal chemistry and bond dissociation processes. Additionally, we follow the homolytic bond breaking process of a Fenton reaction along its reaction coordinate. To investigate the performance and accuracy, we calculate the excitation energies for various transition-metal complexes in typical application scenarios. We discuss the premises, theory, and implementation of the idea, and several of its variations are tested. This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wave function (such as from a Hartree-Fock or Kohn-Sham calculations) based on projectors to targeted atomic valence orbitals.

Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a coordination complex). We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multiconfiguration and multireference (MR) electronic structure calculations. Sayfutyarova, Elvira R Sun, Qiming Chan, Garnet Kin-Lic Knizia, Gerald Automated Construction of Molecular Active Spaces from Atomic Valence Orbitals.

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