Hybrid HF-DFT Research Articles

Reactivity of VC Electrolyte at Li-Metal Electrode: New Insights on SEI Initial Formation from Density Functional Embedding Theory

The metallic lithium (Li) represents the most promising anode material among the next generation of solid-state lithium batteries [1]. An efficient strategy to achieve durable and effective Li-anode batteries is by engineering the solid-electrolyte interphase (SEI) with purposely designed molecules.To this aim, the vinylene carbonate (VC) is one of the most used additives in conventional electrolytes. Some recent experiments proved that the VC promotes the formation of a stable and protective SEI layer between Li metal and electrolyte [2, 3]. Unless the well-known SEI composition, it is difficult to control the VC reactivity, that involves dissociation and polymerization at the electrode surface. Therefore, to dissect these tangled processes, here we present new atomistic insights on VC-Lithium SEI formation via first-principles calculations by Density Functional Embedding Theory (DFET) [4, 5]. Such approach has potentialities for modeling complex reactions at hybrid interfaces in electrocatalysis: it is well suited to combine the best feasible approaches for molecular species (in this case, hybrid HF-DFT for VC molecules and derivatives) and for Li metal electrode (semi-local GGA density functional).Our results highlight different VC dissociation pathways, with formation of reactive radical species and localized cluster of Li2O and Li2CO3. The use of hybrid-DFT-in-DFT embedding is crucial for obtaning energy barriers and qualtitative results in agreement with experiments [3]. Overall, the energetics and structural features of these intermediates improve the current understanding of SEI formation process and can be exploited to drive the reactions toward the desired interfacial properties.[1] J. Janek, W. G. Zeier, Nat Energy 1 (2016) 16141.[2] A. L. Michan et al. Chem. Mater. 28 (2016) 8149.[3] Y. Kamikawa, K. Amezawa, K. Terada, J. Phys. Chem. C 124 (2020) 19937[4] C. Huang, M. Pavone, E. A. Carter, J. Chem. Phys. 134 (2011) 154110[5] C. Huang, A.B. Muñoz-García, M. Pavone, J. Chem. Phys. 145 (2016) 244103

Pure and Hybrid SCAN, rSCAN, and r2SCAN: Which One Is Preferred in KS- and HF-DFT Calculations, and How Does D4 Dispersion Correction Affect This Ranking?

Using the large and chemically diverse GMTKN55 dataset, we have tested the performance of pure and hybrid KS-DFT and HF-DFT functionals constructed from three variants of the SCAN meta-GGA exchange-correlation functional: original SCAN, rSCAN, and r2SCAN. Without any dispersion correction involved, HF-SCANn outperforms the two other HF-DFT functionals. In contrast, among the self-consistent variants, SCANn and r2SCANn offer essentially the same performance at lower percentages of HF-exchange, while at higher percentages, SCANn marginally outperforms r2SCANn and rSCANn. However, with D4 dispersion correction included, all three HF-DFT-D4 variants perform similarly, and among the self-consistent counterparts, r2SCANn-D4 outperforms the other two variants across the board. In view of the much milder grid dependence of r2SCAN vs. SCAN, r2SCAN is to be preferred across the board, also in HF-DFT and hybrid KS-DFT contexts.

Design and Synthesis of the Candesartan Key Intermediate

This paper presents experimental data regarding the synthesis and structural characterization by: 1H-NMR, 13C-NMR, IR spectral analysis, melting point and thin layer chromatography of the candesartan key intermediate: methyl 2-[(tert-butoxycarbonyl)amino]-3-nitrobenzoate. In addition, a computational study of predicted molecular parameters, vibrational wavenumbers, frontier molecular orbitals energy diagram, molecular electrostatic potential map and other electronic distributions maps using restricted hybrid HF-DFT SCF calculation has been performed for obtaining the most stable conformer. For the most Stable conformer has been made a series of DFT calculations using the B3LYP levels using the 6-31G * basis set.

Structure and Properties of Polyfluoride Fn(-) Clusters (n = 3-29).

The electronic and geometrical structures of the neutral Fn and singly negatively charged Fn(-) polyfluorides (n = 3-29) are studied using three levels of theory: density functional theory (DFT) with generalized gradient approximation, hybrid Hartree-Fock-DFT, and hybrid HF-DFT with long-range corrections. For n > 4, each polyfluoride possesses a number of states with different geometries that are closely spaced in total energy. The geometrical structures of the lowest total energy states follow different patterns for the even-n and odd-n Fn(-) anion branches with a preference for higher symmetry geometries. The largest F29(-) anion considered is found to possess Oh symmetry. All the anions beginning with F3(-) are found to possess adiabatic and vertical electron detachment energies exceeding the electron affinities of halogen atoms and are therefore superhalogen anions. Electron affinities, energies of formation, and binding energies show oscillatory behavior as functions of the number n of fluorine atoms. The neutral Fn species are found to be barely stable and are bound by polarization forces. The Fn(-) anions, on the contrary, are quite stable toward the loss of F, F(-), and F2(-), but not to the loss of F2.

Defect Chemistry of CeO2 Surfaces from First Principles and Space Charge Theory

CeO2 (ceria) is a diverse oxide with numerous technologically important functional properties. It is one of the most studied oxygen incorporation materials, and exhibits remarkable catalytic properties towards hydrocarbon and CO oxidation, and water splitting reactions.1-3 Further, acceptor doped ceria is of great interest as electrolyte for solid oxide fuel cells due to its considerable oxide ion conductivity at intermediate temperatures.4 Recently, nanocrystalline CeO2 ceramics were shown to display significant proton conduction even at room temperature,5 suggested to be due to surface, or sub-surface proton migration. The majority of these functional properties are affected by, or even originate from the rich surface, or interface defect chemistry of ceria, and corresponding space charge layers.3 , 6 In this contribution, we explore the defect chemistry of various surface terminations of CeO2 at finite temperatures, by combining first principles calculations and space charge theory. Plane-wave based electronic/atomic structure calculations at the GGA+U and hybrid HF-DFT levels are used to determine bulk defect formation energetics and the defects' surface segregation energies in CeO2. The first principles results are further combined with space charge theory through numerical evaluation of the space charge potential profiles and corresponding defect concentration profiles. The charged oxygen vacancies and protonic defects exhibit highly favorable surface segregation energies, and therefore tend to accumulate on CeO2 surfaces. Although such accumulation is partly charge compensated by oxide and hydroxide ad-ions and Ce3+ species at the surface, the surface turns out to be overall positively charged, and charge-compensated by a negative sub-surface space charge region, at least for low defect concentrations. Under humid conditions, especially at lower temperatures, the surfaces are saturated by protonic species, forming water layers. Finally, the effect of such surface saturation by protonic species, and also H2O monolayer and film formation on the sub-surface space charge potential and defect concentration profiles are discussed. 1. A. Trovarelli, Catalysis Reviews, 1996, 38, 439-520. 2. E. P. Murray, T. Tsai and S. A. Barnett, Nature, 1999, 400, 649-651. 3. Z. A. Feng, F. El Gabaly, X. Ye, Z.-X. Shen and W. C. Chueh, Nat Commun, 2014, 5. 4. H. L. Tuller and A. S. Nowick, Journal of The Electrochemical Society, 1975, 122, 255-259. 5. E. Ruiz-Trejo and J. Kilner, Journal of Applied Electrochemistry, 2009, 39, 523-528. 6. G. Gregori, M. Shirpour and J. Maier, Advanced Functional Materials, 2013, 23, 5861-5867.

Ab InitioPeriodic Simulation of the Spectroscopic and Optical Properties of Novel Porous Graphene Phases

We present a detailed periodic ab initio quantum-mechanical simulation of two recently proposed systems, namely hydrogenated porous graphene (HPG) and biphenyl carbon (BPC), using hybrid HF-DFT functionals and all-electron Gaussian-type basis sets. The equilibrium geometry, the vibrational spectrum (including IR intensities), the full set of components of the polarizability and hyperpolarizability tensors are provided, the latter evaluated through a coupled-perturbed KS/HF scheme. IR and Raman spectra for the two systems are quite different, and differ also from graphene, thus permitting their experimental identification. It is then shown that small defects inserted into the graphene sheet lead to finite values for the in-plane components of the static (hyper)polarizability tensors, spanning a relatively large range of values. By dehydrogenation of porous graphene into biphenyl carbon, a noteworthy enhancement of the nonlinear optical properties through the static second dipole hyperpolarizability can be ...

Confinement effects for ionic carriers in SrTiO3ultrathin films: first-principles calculations of oxygen vacancies

One-dimensional confinement effects are modelled within the hybrid HF-DFT LCAO approach considering neutral and single-charged oxygen vacancies in SrTiO(3) ultrathin films. The calculations reveal that confinement effects are surprisingly short-range in this partly covalent perovskite; already for film thickness of 2-3 nm (and we believe, similar size nanoparticles) only the surface-plane defect properties differ from those in the bulk. This includes a pronounced decrease of the defect formation energy (by ∼1 eV), a much deeper defect band level and a noticeable change in the electronic density redistribution at the near-surface vacancy site with respect to that in the bulk. The results also show that the size effect pertains to the interactions between the oxygen vacancy and two neighboring titanium atoms and orientation (parallel or perpendicular to the surface) of the Ti-V(O)-Ti complex. In particular, we predict considerable oxygen vacancy segregation towards the surface.

LCAO calculation of water adsorption on (001) surface of Y-doped BaZrO 3

The different ways of water molecule adsorption were simulated at (001) ZrO 2-terminated surfaces of Y-doped BaZrO 3 using hybrid HF-DFT method. The water adsorption energies were calculated after the full optimization of atomic positions within the water-slab systems. The proton releasing and hydroxyl group formation was established as result of the exothermic water molecule dissociation. The most favorable proton positions in the surface layers of Y-doped BaZrO 3 were specified. To study the proton diffusion from surface to the deeper layers, the energy barriers were estimated for the proton jumping from one oxygen atom to another.

Hybrid HF–DFT modeling of monolayer water adsorption on (001) surface of cubic BaHfO 3 and BaZrO 3 crystals

First-principles calculations have been used to study the atomic structure, preferred sites and adsorption energies for water adsorption at different terminations of the cubic phase of perovskite-structured BaHfO 3 and BaZrO 3. By considering different initial positions of water molecules, the possibility of water dissociation has been investigated. It is demonstrated that the site selectivity and the form of adsorbed molecule can be affected by the choice of surface unit cell. Dissociative adsorption was found to be favorable for all surfaces in consideration. Hydroxylation of ZrO 2- and HfO 2-terminated surfaces is accomplished by a noticeable reconstruction of the surface structure of cubic phase towards the orthorhombic phase. Calculated atomic charges in bare and hydroxylated surfaces show that BaHfO 3 crystal is slightly more ionic than BaZrO 3.

Ab initio study of bulk and surface iron defects in SrTiO3

Hybrid HF-DFT LCAO approach with B3PW exchange-correlation functional was employed for the calculations of bulk and surface Fe4+ impurities in SrTiO3 for various iron contents. Structural and energetic changes in the host material induced by defect incorporation were particularly addressed. The calculated Jahn-Teller distortion around the iron defects in the bulk were compared with recent experimental EXAFS results. It was found that the iron defects have propensity to segregate to the (001) surface and substantially reduce the basic properties of SrO-terminated surface.

The water adsorption on the surfaces of SrMO3 (M= Ti, Zr, and Hf) crystalline oxides: quantum and classical modelling

Hybrid HF-DFT LCAO simulations of (001) surface properties and water adsorption on cubic SrTiO3, SrZrO3, and SrHfO3 perovskites are performed in a single-slab model framework. The optimized atomic structures and water adsorption energies have been calculated for a single water molecule per the surface unit cell. The possibility of the water molecular dissociation was investigated. Basing on the experimental data and results of the ab initio calculations the new interatomic potentials have been developed to describe the bulk and surface properties of the binary and ternary titanium and zirconium oxides. The proposed force-field takes into account the polarization effects via the shell model. The force-field suggested was used in the molecular mechanics calculations with the extended unit cells to study the possible surface reconstruction upon relaxation and hydroxylation of cubic perovskites.

Dye-Sensitization of the TiO2 Rutile (110) Surface by Perylene Dyes: Quantum-Chemical Periodic B3LYP Computations

The adsorption of perylene derivatives on the rutile TiO2(110) surface was studied by quantum-chemical periodic calculations employing the hybrid HF-DFT functional B3LYP. The perylene molecule, which is a possible constituent of dyes in dye-sensitized solar cells, was functionalized by attachment of phosphonic acid or carboxylic acid groups to permit anchoring to the metal oxide surface. The anchor groups were bound to the molecule directly or via different spacer groups, namely -−CH2−, −CH2−CH2−, and −CHCH−. The effects of the anchor and spacer groups on the adsorption geometry and energy, on the electronic structure of the dye−TiO2 interface, and on the electron transfer rates were investigated. The phosphonic acid anchor group was found to bind the perylene derivatives much more strongly to the surface than the carboxylic acid anchor group. The spacer groups were capable of significantly altering electron transfer rates across the dye−metal oxide interface, where the unsaturated groups permitted inject...

Adsorption of water on (0 0 1) surface of SrTiO 3 and SrZrO 3 cubic perovskites: Hybrid HF-DFT LCAO calculations

Hybrid HF-DFT LCAO simulations of (0 0 1) surface properties and water adsorption on cubic SrZrO 3 and SrTiO 3 perovskites are performed using a single slab model framework. Three slab models with the different surface termination including 6–11 atomic planes were used for calculations. The effect of the symmetry reduction and the role of an extra atomic layer basis set have been considered for the bare surface slabs. The optimized structures and water adsorption energies have been calculated for the various types of surface coverage. It is shown that the formation of H-bonds between the water hydrogens and surface oxygens, as well as between the water molecules themselves, controls the structure of the water adsorption layers on the perovskite surfaces. Obtained results indicate that the dissociative type of water adsorption is the energetically more favourable for SrO-terminated zirconate surface than for similar titanate surface giving evidence to the more basic nature of oxygen atoms on SrO-terminated SrZrO 3 surface.

Electronic structure and bonding studies on triple‐decker sandwich complexes with a P6 middle ring

DFT and hybrid HF-DFT studies of structure and bonding of CpMP6MCp triple-decker sandwich complexes, ranging from 18-28 valence electrons (VE) with M=Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, show that the middle P6 ring complexes adopt symmetric planar (28 valence electron count [VEC]), asymmetric planar (26 VEC), and puckered (24 VEC) geometries. According to the mno Rule, 50 skeletal electrons are needed for these triple-decker cluster frameworks. For 28 VEC, this corresponds to 10 electrons more than the 50 electrons of the mno Rule if all VE of the metal are included. These additional electrons control the distortion of a P6 middle ring and other finer structural details. Completely filled 2a* and 2b* orbitals in 28 VE complexes lead to a planar symmetrical P6 middle ring, while the occupancy in either 2a* or 2b* alone explains the in-plane distortions (asymmetric) in 26 VE complexes. In comparison with 28 VE complexes, the puckering of P6 middle ring in 24 VE complexes is due to the greater stabilization of 5a and the extra stabilization of the +4 oxidation state of Ti. The quintet state of 22 VE complexes is planar as 2a* and 2b* are half filled. Similar geometrical and bonding patterns of CpScP6ScCp and C2P3H2ScC3P3H3ScC2P3H2 support the carbon-phosphorus analogy further. The 18 VE systems, CpScC3B3H6ScCp+ and CpScP3B3H3ScCp+, have the 50 skeletal electrons as stipulated by the mno Rule. Corresponding anions have 52 skeletal electrons (20 VE); the middle rings here are distorted in the plane.

The π-type hydrogen bond with triple C–C bond acting as a proton-acceptor. A gradient-corrected hybrid HF-DFT and MP2 study of the phenol–acetylene dimer in the neutral S 0 ground state

The π-hydrogen bonded minimum on the S 0 ground state potential energy hypersurface (PES) of the neutral phenol–acetylene dimer is located and analyzed in details. Three DFT approaches – B3LYP, mPW1PW91, and PBE1PBE/6-31++G(d,p) along with the MP2/6-31++G(d,p) level of theory were used for the presented analyses. Both the standard and the counterpoise-corrected PESs of the studied dimer were explored. Besides the weak hydrogen-bonding interaction of a π-type, also purely electrostatic interaction of a dipole–quadrupole type between the monomeric units is responsible for the stabilization of this global minimum on the studied PESs. The computed counterpoise-corrected interaction and dissociation energies at all levels of theory are in excellent agreement with the estimations based on experimental spectroscopic data. Anharmonic OH stretching frequencies for the free phenol and the π-hydrogen-bonded phenol–acetylene complex were computed on the basis of 1D DFT and MP2 OH stretching potentials. While all DFT levels significantly overestimate the experimentally measured ν(OH) vibrational frequency shift, the corresponding MP2 value is in excellent agreement with the experimental data (70.2 vs. 68 cm −1). On the other hand, when the frequency shifts are computed within the harmonic approximation, all DFT levels are in fortuitous good agreement with the experiment, due to cancellation of errors. Passing to the counterpoise-corrected PESs has a little influence on the calculated harmonic and anharmonic vibrational frequency shifts of the phenol OH stretching mode. According to the charge-field perturbation analyses of the 1D OH stretching potentials, the purely electrostatic interaction of phenol with the proton-accepting acetylene molecule governs only a small portion of the overall OH vibrational frequency shift, while the role of electrostatics with this respect is more important at MP2 level of theory. However, all levels of theory lead to a conclusion that the dynamical changes of charge-transfer interaction in the course of OH stretching are the main factor governing the IR intensity enhancement of this vibrational transition upon π-hydrogen bonding, while the electrostatic interaction is of a second-order importance with respect to this. According to the second-order perturbation theory analysis of the Fock matrix (or its Kohn–Sham analog) within the NBO basis and the NBO deletion analyses, the charge-transfer between the monomeric units within the dimer is essentially one-directional (occurring from acetylene to phenol), and predominantly of a π → σ* type. The energetic effect of this interaction was estimated as well. The existence of another, much less stable minimum on the explored PESs, predicted on the basis of mainly electrostatic arguments, was also confirmed.

Phosphonic acid adsorption at the TiO 2 anatase (1 0 1) surface investigated by periodic hybrid HF-DFT computations

Phosphonic acid (H 3PO 3) is a candidate as an anchor group that can be used to bind a wide range of molecules to TiO 2 surfaces, with practical applications for example in dye-sensitized solar cells. Adsorption geometries and energies of H 3PO 3 on the TiO 2 anatase (1 0 1) surface have therefore been investigated using quantum-chemical periodic hybrid ab initio Hartree Fock density functional theory calculations employing the B3LYP functional and a split-valence basis set. According to the calculations, the most stable adsorption arrangement is a molecular monodentate configuration with a calculated adsorption energy of 47.1 kcal/mol. There are several additional molecular monodentate and dissociative bidentate adsorption modes with calculated adsorption energies exceeding 40 kcal/mol. For comparison, we have also calculated the adsorption strength of formic acid (HCOOH), which is the currently most widely used anchor group in the solar cell applications, at the same level of theory, to be weaker than 30 kcal/mol. The greater adsorption strength of phosphonic acid compared to formic acid is in good agreement with experimental observations regarding differences in the long-term stability between the two different anchor groups. Implications of the current findings for the design of better dye-sensitized solar cells are discussed.

First principles simulations of F centers in cubic SrTiO 3

Atomic and electronic structure of regular and O-deficient SrTiO3 have been studied. Several types of first principles atomistic simulations: Hartree-Fock method, Density Functional Theory, and hybrid HF-DFT functionals, have been applied to periodic models that consider supercells of different sizes (ranging between 40 and 240 atoms). We confirm the ionic character of the Sr-O bonds and the high covalency of the Ti-O2 substructure. For the stoichiometric cubic crystal; the lattice constant and bulk modulus correctly reproduce the experimental data whereas the band gap is only properly obtained by the B3PW functional. The relaxed geometry around the F center shows a large expansion of the two nearest Ti ions. Moreover, the vacancy formation energy is extremely sensitive to the size and the shape of the supercell as well as the calculation method. The electronic density map indicates the redistribution of two electrons of the missing O atom between the vacancy and 3d atomic orbitals of the two nearest Ti ions, in contrast to the F centers in ionic oxides where the charge centroid does not change. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Functionalization and Kinetic Stabilization of the [4]Paracyclophane System and Aromaticity of Its Extremely Bent Benzene Ring

Kinetic stabilization of the [4]paracyclophane skeleton by the introduction of substituents, which serve to sterically hinder reactions at the reactive bridgehead sites, and properties of the resultant [4]paracyclophanes are investigated in this study. Modification of the property of [4]paracyclophane by functionalization is also intended. [4]Paracyclophanes are designed to be derived from the corresponding Dewar benzene isomers via their photochemical aromatization, and the requisite 1,4-bridged Dewar benzenes bearing sterically demanding functional groups are prepared. Irradiation of these precursors under matrix isolation at 77 K leads to the formation of [4]paracyclophanes, which exhibit characteristic electronic absorption spectra. The half-lives of the generated species vary widely from less than 1 min at -90 degrees C to 0.5 h at -20 degrees C, depending on the type of substituents and the pattern of substitution. One of the derivatives, 24, is stable enough and its content in the irradiated mixture is high enough to permit the measurement of the (1)H NMR spectrum. The recorded spectrum, which is reproduced very well by theoretical calculations using the GIAO method at the hybrid HF-DFT (B3LYP/6-31+G*) level, suggests the sustenance of rather strong diatropicity in its severely bent benzene moiety. Calculations on the bent benzene whose geometry is constrained to that calculated for 24 support that aromaticity is retained to a significant extent as compared to that of planar benzene, as judged by the magnetic criteria of aromaticity, that is, diamagnetic susceptibility exaltation and nucleus-independent chemical shift. The reason for the retention of aromaticity despite the severe bending of the benzene ring is discussed. Cyclophane 24 is so strained that it exceeds the corresponding Dewar benzene precursor in energy and thermally reverts to the latter with a half-life of 15 +/- 5 min at -20 degrees C (DeltaG++ = 18.3 +/- 0.3 kcal mol(-1)).

(57)Fe Mössbauer isomer shifts of heme protein model systems: electronic structure calculations.

We report the results of density functional theory (DFT) calculations of the (57)Fe Mössbauer isomer shifts (delta(Fe)) for a series of 24 inorganic, organometallic, and metalloprotein/metalloporphyrin model systems in S = 0, (1)/(2), 1, (3)/(2), 2, and (5)/(2) spin states. We find an excellent correlation between calculation and experiment over the entire 2.34 mm s(-1) range of isomer shifts: a 0.07-0.08 mm s(-1) rms deviation between calculation and experiment (corresponding to 3-4% of the total delta(Fe) range, depending on the functionals used) with R(2) values of 0.973 and 0.981 (p < 0.0001). The best results are obtained by using the hybrid exchange-correlation functional B3LYP, used previously for (57)Fe Mössbauer quadrupole splittings and (57)Fe NMR chemical shifts and chemical shielding anisotropies. The relativistically corrected value of alpha, alpha(rel), converges with the large basis set used in this work, but the exact values vary somewhat with the methods used: -0.253 a(0)(3) mm s(-1) (Hartree-Fock; HF); -0.316 a(0)(3) mm s(-1) (hybrid HF-DFT; B3LYP), or -0.367 a(0)(3) mm s(-1) (pure DFT; BPW91). Both normal and intermediate spin state isomer shifts are well reproduced by the calculations, as is the broad range of delta(Fe) values: from [Fe(VI)O(4)](2-) (-0.90 mm s(-1) expt; -1.01 mm s(-1) calc) to KFe(II)F(3) (1.44 mm s(-1) expt; 1.46 mm s(-1) calc). Molecular orbital analyses of all inorganic solids as well as all organometallic and metalloporphyrin systems studied reveal that there are three major core MO contributions to rho(tot)(0), the total charge density at the iron nucleus (and hence delta(Fe)), that do not vary with changes in chemistry, while the valence MO contributions are highly correlated with delta(Fe) (R(2) = 0.915-0.938, depending on the functionals used), and the correlation between the valence MO contributions and the total MO contribution is even better (R(2) = 0.965-0.976, depending on the functionals used). These results are of general interest since they demonstrate that DFT methods now enable the accurate prediction of delta(Fe) values in inorganic, organometallic, and metalloporphyrin systems in all spin states and over a very wide range of delta(Fe) values with a very small rms error.

Disrotatory and Conrotatory Transition Structures for the Fe(CO)3-Templated Rearrangement of Methylenecyclopropane to Trimethylenemethane

Hybrid HF-DFT calculations were used to compute the structures and relative energetics of competing disrotatory and conrotatory transition states for ring-opening of Fe(CO)3-complexed methylenecyclopropanes.