A systematic study of the bulk and surface geometrical electronic properties a series transition-metal carbides (TMC with TM = Ti, V, Zr, Nb, Mo, Hf, Ta, W) by first-principles methods is presented. It shown that in these materials chemical bonding strongly covalent, cohesive energies being directly related to bonding-antibonding gap although shift center C(2s) band peak density states respect diamond indicates some metal carbon charge transfer does also take place. The (001) face exhibits...

Abstract The mechanism of the light‐induced spin crossover [Fe(bpy) 3 ] 2+ complex (bpy=2,2′‐bipyridine) has been studied by combining accurate electronic‐structure calculations and time‐dependent approaches to calculate intersystem‐crossing rates. We investigate how initially excited metal‐to‐ligand charge transfer (MLCT) singlet state deactivates final metastable high‐spin state. Although ultrafast X‐ray free‐electron spectroscopy established that total timescale this process is on order a...

Engineering the bandgap of O-terminated MXenes for photocatalytic water splitting reveals Zr 2 CO as a suitable photocatalyst.

The performance of the complete active space second-order perturbation theory (CASPT2) to accurately predict magnetic coupling in a wide series molecules and solid state compounds has been established. It is shown that CASPT2, based on reference wave function only includes effects described by Anderson or Hay−Thibeault−Hoffmann model, correctly reproduces all experimental trends. For quantitative agreement with experiment (or accurate results arising from difference dedicated configuration...

Ab initio calculations have been performed on [Fe(II)(bpy)3](2+) (bpy = bipyridine) to establish the variation of energy electronic states relevant light-induced excited-state spin trapping as a function Fe-ligand distance. Light-induced crossover takes place after excitation into singlet metal-to-ligand charge-transfer (MLCT) band. We found that corresponding their minimum in same region low-spin (LS) state and dependence triplet MLCT are nearly identical (1) states. The high-spin (HS) is...

The key parameters associated to the thermally induced spin crossover process have been calculated for a series of Fe(II) complexes with mono-, bi-, and tridentate ligands. Combination density functional theory calculations geometries normal vibrational modes, highly correlated wave function methods energies, allows us accurately compute entropy variation transition zero-point corrected energy difference between low- high-spin states. From these values, temperature, T1/2, is estimated...

We present an analysis of the M-O chemical bonding in binary oxides MgO, CaO, SrO, BaO, and ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ based on ab initio wave functions. The model used to represent local environment a metal cation bulk oxide is M${\mathrm{O}}_{6}$ cluster which also includes effect lattice Madelung potential. functions for these clusters leads conclusion that all alkaline-earth must be regarded as highly ionic oxides; however, character decreases one goes from almost perfectly...

In this work we discuss the interaction of an adsorbate on ionic surface taking as representative example CO a perfect MgO(100) surface. The main goal is to investigate different contributions and how model them by using finite cluster model. To end use three ab initio Hartree-Fock approaches. First, convergence properties array point charges used simulate Madelung potential. Next, large models show that there oscillatory behavior energy. We rather clusters are needed avoid such...

Ab initio calculations have been performed on Fe (II) (tz) 6 (tz = 1- H-tetrazole) to establish the variation of energy electronic states relevant (reverse) light-induced excited-state spin trapping (LIESST) as function Fe-ligand distance. Equilibrium distances and absorption energies are correctly reproduced. The deactivation excited singlet is proposed occur in Franck-Condon region through overlap vibrational with an intermediate triplet state or intersystem crossing along asymmetric mode....

Core level binding energies, directly measured by X-ray photoelectron spectroscopy (XPS), provide unique information regarding the chemical environment of atoms in a given system. However, interpretation XPS extended systems may not be straightforward and requires assistance from theory. The different state-of-the-art theoretical methods commonly used to approach core energies their shifts with respect reference are reviewed critically assessed special emphasis on recently developed focus...

In this paper, we present a study of the signs and magnitudes errors theoretical binding energies, BE's, C(1s) O(1s) core-levels compared to BE's measured in X-Ray photoemission, XPS, experiments. particular, explain unexpected sign error Hartree-Fock BE, which is larger than experiment, terms correlation effects due near degeneracy CO(1π) CO(2π) levels show how taking into account leads rather accurate predicted BE's. We separate initial state contributions degeneracy, for ground...

X-ray photoelectron spectroscopy (XPS) applied to N-doped graphene leads a rather broad N(1s) core level signal that, based on different sources available in the literature, is most often interpreted by fitting experimental spectra three peaks. The resulting features are assigned graphitic, pyrrolic, and pyridinic nitrogen, even if these far from being uniquely defined literature. This broadly accepted interpretation has been questioned recent accurate Hartree–Fock calculations concluding...

Finding appropriate photocatalysts for solar‐driven water (H 2 O) splitting to generate hydrogen ) fuel is a challenging task, particularly when guided by conventional trial‐and‐error experimental methods. Here, density functional theory (DFT) used explore the MXenes photocatalytic properties, an emerging family of two‐dimensional (2D) transition metal carbides and nitrides with chemical formula M n+ 1 X n T x , known be semiconductors having terminations. More than 4,000 MXene structures...

Charged and neutral oxygen vacancies in the bulk on perfect defective surfaces of MgO are characterized as quantum-mechanical subsystems chemically bonded to host lattice containing most charge left by removed oxygens. Attractors electron density appear inside vacancy, a necessary condition for existence subsystem according atoms molecules theory. The analysis localization function also shows attractors at vacancy sites, which associated basin shared with valence domain nearest This...

In the present paper, a density functional systematic study of adsorption atomic oxygen on (001) surface several transition-metal carbides (TMC, TM = Ti, Zr, Hf, V, Nb, Ta, Mo) is reported. Our calculations using both PW91 and RPBE exchange correlation functionals show that group 4, TMC (100) atoms highly prefer hollow sites surrounded by one carbon atom two metal (MMC). On rest 5 6, competition between this site top (M-top) observed. A third possible competitive found for δ-MoC site, where...

A systematic density functional study of the adsorption and dissociation O2 on (001) surface several transition metal carbides (TCMs; TM = Ti, Zr, Hf, V, Nb, Ta, Mo) is presented. It found that may adsorb molecularly two different sites with similar energy. At these sites, either bridges (M) atoms or it placed directly top a M atom. case apart δ-MoC, where Mo far up in energy respect to bridging atoms. The relative stability TMCs dominated by electron back-donation between stabilization...

Abstract A simple procedure devised to obtain optimized point charges represent the Madelung potential is reported and applied six different crystal structures occurring in ionic systems. Their use ab initio cluster model calculations discussed through some selected examples results compared with those arising from of well‐known Evjen method. © 1993 John Wiley & Sons, Inc.

The nature of the chemical bond in three titanium oxides different crystal structure and formal oxidation state has been studied by means ab initio cluster-model approach. covalent ionic contributions to have measured from theoretical techniques. All analysis is consistent with an increasing covalence TiO, ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{TiO}}_{2}$ series as expected intuition. Moreover, use approach combined techniques permitted us quantify degree character, showing that...

Abstract The light‐induced spin crossover in Fe II complexes is studied with complete active space second‐order perturbation theory. potential energy surfaces of the low‐spin and high‐spin states are determined as function Fe‐‐ligand distance interpolating between equilibrium geometries. In addition, we calculate relative energies lowest excited ${\rm Fe}-3{\rm d}^6$ along this coordinate. To address mechanism crossover, metal‐to‐ligand charge transfer singlet, triplet, quintet coupling were...

The electronic structure of bulk corundum(α-Al2O3) has been studied by using ab initio cluster model Hartree–Fock self-consistent-field (SCF) and configuration interaction (CI) wave functions. An array optimized point charges surrounding the is used to represent Madelung field. Different analyses energetic chemical bond contributions functions have performed. These include constrained space orbital variations (CSOV), use projection operator techniques, decomposition on ground state SCF...