Empty Electronic States Research Articles

The Electronic Structure of Transition Metal (TM) Oxides for the Oxygen Evolution Reaction: The Critical Role of TM 3d Hole State

Electrolysis of water to produce hydrogen and oxygen is a promising pathway for the storage of renewable energy in form of chemical fuels. The efficiency of the overall process is usually limited by the sluggish kinetics of the oxygen evolution reaction (OER) due to a complex four-electron/proton transfer mechanism. Therefore, the most crucial step for water electrolysis to become a widespread industrial process is to develop efficient electrocatalysts capable of driving the OER at a low overpotential.[1,2] In this talk, I will summaries the key electronic features that induces high catalytic activity towards the oxygen evolution reaction of trivalent transition metal (TM) oxides with perovskite structure, such as LaCoO3 [3] and LaFeO3.[4] The partial substitution of La for Sr in LaTMO3 results in the oxidation of TM3+ to TM4+ and substantially enhances OER catalytic activity. A comprehensive X-ray spectroscopic study, based on in-situ XPS and XAS, reveals a strong correlation of the enhanced OER catalytic activity with the presence of cations in the 4+ oxidation state. Increasing the concentration of TM cations in the 4+ oxidation state leads to a more covalent TM–O bond due to higher TM 3d–O 2p orbital hybridization and shifts the energy position of the valence band (VB) closer to the Fermi level (E F). Such an electronic modulation optimizes the surface adsorption energetics of *OH intermediates, contributing to faster OER kinetics. Furthermore, the oxidation of TM3+ to TM4+ creates a new unoccupied state (hole state) below the conduction band, associated with the formation of TM 3d empty electronic states. This hole states reduce the energy barrier for electron transfer associated with the OER, as illustrated in the figure below, thereby facilitating charge transfer at the interface during the reaction.Figure 1: Key electronic features of transition metal (TM) oxides for the oxygen evolution reaction

Interdisciplinary Fundamental Concepts in STEM: Solid State Physics and COVID-19 Pandemic Evolution

The rapid development of computer-aided design tools, such as MATLAB or Octave, or Mathematica enabled students to solve many complicated problems focusing less on underlying STEM-related concepts that are interdisciplinary. Therefore, it is important to demonstrate how it could be done using specific examples that could be linked to different subjects or even to their everyday life experience. This paper reports on using the COVID-19 pandemic evolution model (Shur, 2022) in my class on the physics of advanced semiconductors devices. I use this model to show how the concepts, such as the Born-Oppenheimer approximation and Fermi-Dirac distribution function could be used in a completely different STEM field. In solid-state physics, the Born-Oppenheimer approximation is used to separate rapid electronic motion, relevant to the electronic states and much slower nuclei motion (since nuclei are thousands of times heavier than electrons). Likewise, the COVID-19 model uses a relatively fast pandemic evolution growth or decay constant, a slow function of time itself. In solid-state physics, the Fermi-Dirac distribution function describes the transition from the occupied electronic states to empty electron states with the temperature determining the transition interval. The COVID-19 model uses the generalized Fermi-distribution function to describe the mitigation measures that determine the transition from a high to a lower infection rate. A more accurate COVID-19 evolution model requires a generalized Fermi-Dirac function that accounts for a slow variation of the effect of the mitigation measures with time. In turn, this generalization could be used in solid-state physics to describe the electron temperature increase in the electric field.

Formal Valence, Charge Distribution, and Chemical Bond in a Compound with a High Oxidation State: KMnO4

KMnO4 has unusual formal manganese oxidation state Mn+7 that seems puzzling: the energy of creating such ion (119 eV) is much greater than the energy of chemical bonds (up to ~10 eV). We have used the Wannier functions formalism to analyze the distribution of Mn-3d electrons and O-2p electrons for empty electronic states in the {text{MnO}}_{4}^{ - } complex and have found that, while formally one has {{d}^{0}} configuration for manganese ion in this compound, in reality only about one-half of the hole density described by these Wannier functions corresponding to this configuration belongs to d-electrons, while the other half is spread over surrounding oxygen atoms. This corresponds much more to Mn+7 state than to Mn+2, because the calculated total number of d‑electrons is equal to 5.25. Our analysis has also sown nearly perfect covalent type of chemical bond within the {text{MnO}}_{4}^{ - } complex with negligible contribution of the ionic part.

TurboMagnon – A code for the simulation of spin-wave spectra using the Liouville-Lanczos approach to time-dependent density-functional perturbation theory

We introduce turboMagnon, an implementation of the Liouville-Lanczos approach to linearized time-dependent density-functional theory, designed to simulate spin-wave spectra in solid-state materials. The code is based on the noncollinear spin-polarized framework and the self-consistent inclusion of spin-orbit coupling that allow to model complex magnetic excitations. The spin susceptibility matrix is computed using the Lanczos recursion algorithm that is implemented in two flavors - the non-Hermitian and the pseudo-Hermitian one. turboMagnon is open-source software distributed under the terms of the GPL as a component of Quantum ESPRESSO. As with other components, turboMagnon is optimized to run on massively parallel architectures using native mathematical libraries (LAPACK and FFTW) and a hierarchy of custom parallelization layers built on top of MPI. The effectiveness of the code is showcased by computing magnon dispersions for the CrI3 monolayer, and the importance of the spin-orbit coupling is discussed. Program summaryProgram title:turboMagnonCPC Library link to program files:https://doi.org/10.17632/6zxwzv5dt4.1Licensing provisions: GNU General Public License V 2.0Programming language: Fortran 95External routines:turboMagnon is a tightly integrated component of the Quantum ESPRESSO distribution and requires the standard libraries linked by it: BLAS, LAPACK, FFTW, MPI.Nature of problem: Calculation of the spin-wave spectra for solid-state materials.Solution method: The spin susceptibility matrix of a periodic system is expressed in terms of the resolvent of its Liouvillian superoperator within time-dependent density-functional perturbation theory. It is calculated using non-Hermitian or pseudo-Hermitian variants of the Lanczos recursion scheme, whose implementation does not require the calculation of empty electronic states. Norm-conserving pseudopotentials are used in conjunction with plane-wave basis sets and periodic boundary conditions. Relativistic effects (spin-orbit coupling) can be included in calculations.Additional comments including restrictions and unusual features: Linear-response regime only. Collinear spin-polarized formalism is not supported, only noncollinear spin-polarized case can be used. Adiabatic LSDA exchange-correlation functionals only (no GGA, no meta-GGA, no hybrid functionals, no Hubbard U, etc.). No ultrasoft and projector-augmented-wave pseudopotentials. No symmetry.Empty states are not used, nor even calculated. Three Lanczos recursions give access to the whole spectrum of magnetic excitations at fixed transferred momentum; one Lanczos recursion is enough for a specific orientation of the magnetic field and the ground-state magnetization of the system.The distribution file of this program can be downloaded from the Quantum ESPRESSO website: http://www.quantum-espresso.org/, and the development version of this program can be downloaded via Git from the GitLab website: https://gitlab.com/QEF/q-e. Interactions with end users of the turboMagnon code happen via a mailing-list forum of Quantum ESPRESSO: https://www.quantum-espresso.org/forum. Documentation of the turboMagnon code is tightly coupled with the code and is done via standard code comments.

Hard-wall edge confinement in two-dimensional topological insulators and the energy of the Dirac point

In 2D topological insulators (TIs) based on semiconductor quantum wells such as HgTe/CdTe, hard wall spin-polarized edge states are calculated from an $8\ifmmode\times\else\texttimes\fi{}8$ linear-$k$ multiband (LKMB) Hamiltonian based directly on $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ theory, and from a $4\ifmmode\times\else\texttimes\fi{}4$ BHZ Hamiltonian derived from it by the elimination of remote states using perturbation theory. Both approaches lead to similar results with standard boundary conditions obtained by integrating the eigenstate equation across an interface (SBCs). In contrast, open boundary conditions (OBCs) yield unphysical results and do not work for the LKMB Hamiltonian. Their failure is traced to a spurious solution introduced by the elimination process. In the BHZ treatment, SBCs are shown to be consistent with perturbation theory on both sides of the boundary, and a wall hybridization parameter is estimated for a vacuum using a basis of empty crystal free electron states. A Dirac point is not expected for a vacuum, but can exist when a thin passivation layer is used whose midgap energy is nearly degenerate with that of the TI. In the absence of interface band mixing (IBM), the Dirac point is then very close to midgap and virtually independent of the TI band asymmetry. IBM introduces a significant energy shift, which decreases monotonically with edge state wave vector. Using SBCs, the paradoxical extension of the BHZ edge states across the topological phase transition is also resolved.

Electronic structure of the [Ni(Salen)] complex studied by core-level spectroscopies.

The nature and structure of occupied and empty valence electronic states (molecular orbitals, MOs) of the [Ni(Salen)] molecular complex (NiO2N2C16H14) have been studied by X-ray photoemission and absorption spectroscopy combined with density functional theory (DFT) calculations. As a result, the composition of the high-lying occupied and low-lying unoccupied electronic states has been identified. In particular, the highest occupied molecular orbital (HOMO) of the complex is found to be predominantly located on the phenyl rings of the salen ligand, while the states associated with the occupied Ni 3d-derived molecular orbitals (MOs) are at higher binding energies. The lowest unoccupied molecular orbital (LUMO) is also located on the salen ligand and is formed by the 2pπ orbitals of carbon atoms in phenyl groups of the salen macrocycle. The unoccupied MOs above the LUMO reflect σ- and π-bonding between Ni and its nearest neighbours. All valence states have highly mixed character. The specific nature of the unoccupied Ni 3d-derived σ-MO is a consequence of donor-acceptor chemical bonding in [Ni(Salen)].

Electronic properties of carbon nanotubes as detected by photoemission and inverse photoemission

The relation between morphology and energy level alignment in carbon nanotubes (CNT) is a crucial information for the optimization of applications in nanoelectronics, optics, mechanics and (bio)chemistry. Here we present a study of the relation between the electronic properties and the morphology of single wall CNT (SWCNT), aligned multi wall CNT (MWCNT) and unaligned MWCNT. The CNT were synthesized via catalytic chemical vapor deposition in ultra-high vacuum conditions. Combined ultraviolet photoemission and inverse photoemission (IPES) spectra reveal a high sensitivity to the nanotube morphology. In the case of unaligned SWCNT the distinctive unoccupied Van Hove singularities (vHs) features are observed in the high resolution IPES spectra. Those features are assigned to semiconducting and metallic SWCNT states, according to calculated vHs DOS. The two MWCNT samples are similar in the diameter of the tube (about 15 nm) and present similar filled and empty electronic states, although the measured features in the aligned MWCNT are more defined. Noteworthy, interlayer states are also revealed. Their intensities are directly related to the MWCNT alignment. Focussing and geometrical effects associated to the MWCNT alignment are discussed to account the spectral differences.

Empty electron states in cobalt-intercalated graphene.

The dispersion of the electronic states of epitaxial graphene (Gr) depends significantly on the strength of the bonding with the underlying substrate. We report on empty electron states in cobalt-intercalated Gr grown on Ir(111), studied by angle-resolved inverse photoemission spectroscopy and x-ray absorption spectroscopy, complemented with density functional theory calculations. The weakly bonded Gr on Ir preserves the peculiar spectroscopic features of the Gr band structure, and the empty spectral densities are almost unperturbed. Upon intercalation of a Co layer, the electronic response of the interface changes, with an intermixing of the Gr π* bands and Co d states, which breaks the symmetry of π/σ states, and a downshift of the upper part of the Gr Dirac cone. Similarly, the image potential of Ir(111) is unaltered by the Gr layer, while a downward shift is induced upon Co intercalation, as unveiled by the image state energy dispersion mapped in a large region of the surface Brillouin zone.

Electronic structure of pristine and Ni-substituted LaFeO3 from near edge x-ray absorption fine structure experiments and first-principles simulations

We present a joint theoretical and experimental study of the oxygen $K$-edge spectra for LaFeO$_3$ and homovalent Ni-substituted LaFeO$_3$ (LaFe$_{0.75}$Ni$_{0.25}$O$_3$), using first-principles simulations based on density-functional theory with extended Hubbard functionals and x-ray absorption near edge structure (XANES) measurements. Ground-state and excited-state XANES calculations employ Hubbard on-site $U$ and inter-site $V$ parameters determined from first principles and the Lanczos recursive method to obtain absorption cross sections, which allows for a reliable description of XANES spectra in transition-metal compounds in a very broad energy range, with an accuracy comparable to that of hybrid functionals but at a substantially lower cost. We show that standard gradient-corrected exchange-correlation functionals fail in capturing accurately the electronic properties of both materials. In particular, for LaFe$_{0.75}$Ni$_{0.25}$O$_3$ they do not reproduce its semiconducting behaviour and provide a poor description of the pre-edge features at the O $K$ edge. The inclusion of Hubbard interactions leads to a drastic improvement, accounting for the semiconducting ground state of LaFe$_{0.75}$Ni$_{0.25}$O$_3$ and for a good agreement between calculated and measured XANES spectra. We show that the partial substitution of Fe for Ni affects the conduction-band bottom by generating a strongly hybridized O($2p$)-Ni($3d$) minority-spin empty electronic state. The present work, based on a consistent correction of self-interaction errors, outlines the crucial role of extended Hubbard functionals to describe the electronic structure of complex transition-metal oxides such as LaFeO$_3$ and LaFe$_{0.75}$Ni$_{0.25}$O$_3$ and paves the way to future studies on similar systems.

Synthesis and electrochemical performance of Co1−xNixS QDs as electrode materials for high performance supercapacitors

Ni atom doping increases the density of Co's and S's empty electron states and increases the specific capacitance.

MICRO-EMULSION METHOD FOR THE SYNTHESIS AND CHARACTERIZATION OF La, Mn-DOPED Ba3Co2 Fe24O41 Z-TYPE HEXA-NANOFERRITES

In this report, micro-emulsion method was used to obtain La, Mn-doped Ba3Co2 [Formula: see text][Formula: see text] single-phase Z-type hexa-nanoferrites by maintaining annealing temperature at 1200∘C. X-ray diffraction (XRD) analysis shows lattice parameters, crystallite size, and volume are significantly enhanced by introducing La and Mn ions instead of Ba and Fe, respectively. Moreover, La and Mn ion doping improved the preferred orientation of atoms through the basal plane of Z-type hexaferrite. Field emission scanning electron microscopy (FESEM) study reveals that the surface morphology of La- and Mn-doped Ba3Co2 [Formula: see text][Formula: see text], Z-type ferrites show ultrafine and small particle size. The analysis of X-Ray absorption near edge spectroscopy (XANES) suggests that transition in [Formula: see text] has occurred from 3d core level to empty electronic state above the Fermi level. Furthermore, it is observed that in the Z-type ferrites Co exist as divalent ion and Fe as trivalent ion by analyzing XANES. Vibrating samples magnetometer (VSM) indicated that the samples are ferromagnetic as they have narrow hysteresis loops. The decrease in coercivity is due to paramagnetic dopant element Manganese (Mn).

Scalable GW software for quasiparticle properties using OpenAtom

The GW method, which can describe electronic excitations accurately, is a powerful ab initio electronic structure technique in molecular, condensed matter and materials physics. However, the applications of the GW method to large systems require supercomputers and efficient fine-grained parallel software to overcome the computational complexity and expense of the method which scales as O(N4). Here, we develop fine-grained parallel GW software for the plane-wave basis. We proceed by revisiting the standard GW formulae in order to discern the optimal approaches for each phase of the GW calculation on present day supercomputers and to take into account recent methodological advances to inform our choices. These best numerical practices are implemented in the OpenAtom software which is written on top of the Charm++ parallel framework. We then evaluate the performance of the new software for a wide range of system sizes. Our GW software shows significantly improved parallel scaling compared to publicly available GW software on the Mira and Blue Waters supercomputers, two of most powerful computing platforms in the world. Program summaryProgram title: OpenAtom-GWProgram files doi:http://dx.doi.org/10.17632/pvj723crcx.1Licensing provisions: BSD 3-clauseProgramming language: C++Nature of problem: The GW method describes electronic excitations in materials: the energetics and quantum wave behavior when electrons are added or removed from a material. The GW method scales as O(N4) where N is the number of atoms in the simulation cell. The input variables for GW method are single-particle electronic states computed from mean-field calculations such as Density Functional Theory (DFT). The GW method, which is a proper quasiparticle approach, provides corrections to the mean-field electronic state information that include physics beyond DFT to treat excitations. We employ a plane-wave basis set as is common in condensed matter and materials physics.Solution method: The first step is to construct the static polarizability matrix (P) which represents the response of the electronic density with respect to changes in the electronic potential, and whose construction is the most expensive part of a GW computation. The P matrix calculation requires a large dense spatial grid (real space) and has a double summation over filled and empty electronic states requiring outer product operations. A large number of Fast Fourier Transforms (FFTs) must also be performed. Next, the polarizability is employed to compute the self-energy which represents the dynamic potential acting upon moving electrons. We employ a real-space representation of static polarizability matrix because the real-space method reduces the number of FFTs and the size of the real-space grids compared to working solely in the Fourier (g-space) representation. Parallelization is carried out using the Charm++ parallel middleware which through overdecomposition and virtualization, supports and enables highly scalable fine-grained parallel applications.Additional comments including restrictions and unusual features: Users need to run a DFT calculation using, e.g., the Quantum Espresso software or OpenAtom itself, to obtain the input electronic states (i.e., single particle wavefunctions and energies). Since the OpenAtom-GW software is written on top of Charm++ parallel middleware, the user must install Charm++; however, Charm++ is an increasingly widely used framework in scientific computing and this requirement does not present a bottleneck to usage.

Abnormally Strong Electron–Phonon Scattering Induced Unprecedented Reduction in Lattice Thermal Conductivity of Two-Dimensional Nb2C

In most materials the electron-phonon (e-p) scattering is far weaker than phonon-phonon (p-p) scattering, and the e-p scattering is usually proportional to the e-p coupling strength. Here, we report strong e-p scattering but low e-p coupling strength in two-dimensional(2D) Nb2C by first-principles calculations. Moreover, the intensity of e-p scattering is close to that of p-p scattering at 300 K in sharp contrast to normal cases. This abnormal e-p scattering is understood by a specific feature that the energy difference between occupied and empty electron states near the Fermi level is in the order of the characteristic phonon energy. By calculating the phonon transport property of 2D Nb2C, we show that this strong e-p scattering can result in great reduction in the lattice thermal conductivity.Our work also highlights a new way for searching novel 2D materials with low lattice thermal conductivity.

Observation of intercalation-driven zone folding in quasi-free-standing graphene energy bands

Two-photon photoemission measurements reveal a near-zero-dispersion empty electronic state, approximately 2.6 eV above the Fermi energy and near the Brillouin zone center, induced by oxygen intercalation at the graphene-Ir(111) interface. While oxygen intercalation leads to quasi-free-standing graphene, electron diffraction shows $2\ifmmode\times\else\texttimes\fi{}2$ periodicity due to the patterned intercalant. Near the zone center, large-wave-vector zone folding, driven by this $2\ifmmode\times\else\texttimes\fi{}2$ periodicity, replicates states from near the Dirac cone that have little dispersion due to trigonal warping, explaining the nearly flat band. The zone-folding mechanism is supported by results from angle-resolved photoemission measurements and from density-functional-theory-based calculations of the unfolded energy bands. These results demonstrate zone-folding effects in graphene on a wave vector and energy scale that has largely been unexplored, and may open new opportunities to engineer the graphene electronic states.

Double-Layer Polymer Electrolyte for High-Voltage All-Solid-State Rechargeable Batteries.

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite-free plating of a lithium-metal anode and a Li+ extraction from an oxide host cathode without electrolyte oxidation in a high-voltage cell during the charge process. Therefore, a double-layer polymer electrolyte is investigated, in which one polymer provides dendrite-free plating of a Li-metal anode and the other allows a Li+ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium-metal anode and a poly(N-methyl-malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li+ conductivity on crossing the polymer/polymer interface.

Atomic and electronic structure of the Si(331)-(12 1) surface.

We report on the investigation of the atomic and electronic structures of a clean Si(331)-(12 × 1) surface using a first-principles approach with both plane wave and strictly localized basis sets. Starting from the surface structure proposed by Zhachuk and Teys [Phys. Rev. B 95, 041412(R) (2017)], we develop significant improvements to the atomic model and localized basis set which are critical for the correct description of the observed bias dependence of scanning tunneling microscopy (STM) images. The size mismatch between the Si pentamers from the surface model and those seen by STM is explained within the context of the Tersoff-Hamann model. The energy barriers that separate different Si(331) buckled configurations were estimated, showing that the surface structure is prone to dynamic buckling at room temperature. It is found that empty electronic states on Si(331) are essentially localized on the pentamers with interstitials and under-coordinated Si sp 2-like atoms between them, while filled electronic states are localized on under-coordinated Si sp 3-like atoms and dimers on trenches. The calculated electronic density of states exhibits two broad peaks in the fundamental bandgap of Si: one near the valence band top and the other near the conduction band bottom. The resulting surface bandgap of 0.58 eV is in an excellent agreement with spectroscopy studies.

Understanding trends in lithium binding at two-dimensional materials

Layered structure and peculiar electronic properties of two-dimensional (2D) materials foster the concept of utilizing them as main components of lithium-ion batteries. Understanding basic physical mechanisms governing the interaction of Li with 2D crystals is of key importance to succeeding in a rational design of cathode and anode materials with superior functionalities. In this study density functional theory was applied to reveal the microscopic picture of Li interaction with 15 2D crystals, including several transition metal oxides and dichalcogenides, carbides of Group XIV elements, functionalized graphene, silicene, and germanene, as well as black phosphorus and ${\mathrm{Ti}}_{2}\mathrm{C}$ MXene. We found that the general trend in Li binding can be estimated from positions of conduction band minima of 2D materials, since the energy of the lowest empty electronic states shows a nice correlation with the strength of Li adsorption. At variance to the majority of studied surfaces where the electron transferred from Li is spread across the substrate, in monolayers of carbides of Group XIV elements the interaction with Li and the charge transfer are well localized. This gives rise to their capability to accommodate Li structures with a nearly constant binding energy of alkaline atoms over Li coverages ranging from well-separated adatoms to a full monolayer.

Identifying Electronic Modes by Fourier Transform from δ-Kick Time-Evolution TDDFT Calculations

Time-dependent density-functional theory (TDDFT) is widely used for calculating electron excitations in clusters and large molecules. For optical excitations, TDDFT is customarily applied in two distinct approaches: transition-based linear-response TDDFT (LR-TDDFT) and the real-time formalism (RT-TDDFT). The former directly provides the energies and transition densities of the excitations, but it requires the calculation of a large number of empty electron states, which makes it cumbersome for large systems. By contrast, RT-TDDFT circumvents the evaluation of empty orbitals, which is especially advantageous when dealing with large systems. A drawback of the procedure is that information about the nature of individual spectral features is not automatically obtained, although it is of course contained in the time-dependent induced density. Fourier transform of the induced density has been used in some simple cases, but the method is, surprisingly, not widely used to complement the RT-TDDFT calculations; although the reliability of RT-TDDFT spectra is now widely accepted, a critical assessment for the corresponding transition densities and a demonstration of the technical feasibility of the Fourier-transform evaluation for general cases is still lacking. In the present work, we show that the transition densities of the optically allowed excitations can be efficiently extracted from a single δ-kick time-evolution calculation even in complex systems like noble metals. We assess the results by comparison with the corresponding LR-TDDFT ones and also with the induced densities arising from RT-TDDFT simulations of the excitation process.

111-Type Semiconductor ReGaSi Follows 14e- Rules.

Electron-counting rules were applied to understand the stability, structural preference, and physical properties of metal disilicides. Following predictions made by 14 electron counting rules, the ordered semiconductor ReGaSi, the first ternary phase in this system, was proposed and successfully synthesized. It crystallizes with a primitive tetragonal structure (space group P4/nmm) closely related to that of MoSi2-type ReSi2, but with Ga and Si orderly distributed in the unit cell. The band structure, density of states, and crystal orbital calculations confirm the electron count hypothesis to predict new stable compounds. Calculations, based on 14 electrons per ReGaSi units, show a small indirect band gap of ∼0.2 eV around Fermi level between full and empty electronic states. Additionally, first-principles calculations confirm the site preference of Ga and Si, which is observed through the structural refinement. Experimental magnetic measurements verified the predicted nonmagnetic properties of ReGaSi.

Electronic structure of nickel porphyrin NiP: Study by X-ray photoelectron and absorption spectroscopy

Energy distributions and properties of the occupied and empty electronic states for a planar complex of nickel porphyrin NiP are studied by X-ray photoemission and absorption spectroscopy techniques. As a result of the analysis of the experimental spectra of valence photoemission, the nature and energy positions of the highest occupied electronic states were determined: the highest occupied state is formed mostly by atomic states of the porphine ligand; the following two states are associated with 3d states of the nickel atom. It was found that the lowest empty state is specific and is described by the σ-type b1g MO formed by empty \(Ni3{d_{{x^2} - {y^2}}}\)-states and occupied 2p-states of lone electron pairs of nitrogen atoms. This specific nature of the lowest empty state is a consequence of the donor–acceptor chemical bond in NiP.