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Zirconium-based alloys are used in water-cooled nuclear reactors for both nuclear fuel cladding and structural components. Under this harsh environment, the main factor limiting the service life of zirconium cladding, and hence fuel burn-up efficiency, is water corrosion. This oxidation process has recently been linked to the presence of a sub-oxide phase with well-defined composition but unknown structure at the metal-oxide interface. In this paper, the combination of first-principles materials modeling and high-resolution electron microscopy is used to identify the structure of this sub-oxide phase, bringing us a step closer to developing strategies to mitigate aqueous oxidation in Zr alloys and prolong the operational lifetime of commercial fuel cladding alloys. [ABSTRACT FROM AUTHOR]

Magic-angle spinning (MAS) NMR spin-echo dephasing is systematically investigated for the spin I= 3/2 11B nucleus in lithium diborate, Li2O·2B2O3. A clear dependence on the quadrupolar frequency (ωPASQ/2π= 3CQ/[4I(2I− 1)]) is observed: the B3 (larger CQ) site dephases more slowly than the B4 site at all investigated MAS frequencies (5 to 20 kHz) at 14.1 T. Increasing the MAS frequency leads to markedly slower dephasing for the B3 site, while there is a much less evident effect for the B4 site. Considering samples at 5, 25, 80 (natural abundance) and 100% 11B isotopic abundance, dephasing becomes faster for both sites as the 11B isotopic abundance increases. The experimental behaviour is rationalised using density matrix simulations for two and three dipolar-coupled 11B nuclei. The experimentally observed slower dephasing for the larger CQ(B3) site is reproduced in all simulations and is explained by the reintroduction of the dipolar coupling by the so-called “spontaneous quadrupolar-driven recoupling mechanism” having a different dependence on the MAS frequency for different quadrupolar frequencies. Specifically, isolated spin-pair simulations show that the spontaneous quadrupolar-driven recoupling mechanism is most efficient when the quadrupolar frequency is equal to twice the MAS frequency. While for isolated spin-pair simulations, increasing the MAS frequency leads to faster dephasing, agreement with experiment is observed for three-spin simulations which additionally include the homogeneous nature of the homonuclear dipolar coupling network. First-principles calculations, using the GIPAW approach, of the 2J11B−11Bcouplings in lithium diborate, metaborate and triborate are presented: a clear trend is revealed whereby the 2J11B−11Bcouplings increase with increasing B–O–B bond angle and B–B distance. However, the calculated 2J11B−11Bcouplings are small (0.95, 1.20 and 2.65 Hz in lithium diborate), thus explaining why no zero crossing due to Jmodulation is observed experimentally, even for the sample at 25% 11B where significant spin-echo intensity remains out to durations of ∼200 ms. [ABSTRACT FROM AUTHOR]

High-resolution 19F magic angle spinning (MAS) NMR spectroscopy is used to study disorder and bonding in a crystalline solid. 19F MAS NMR reveals four distinct F sites in a 50% fluorine-substituted deuterated hydrous magnesium silicate (clinohumite, 4Mg2SiO4·Mg(OD1-xFx)2 with x = 0.5), indicating extensive structural disorder. The four 19F peaks can be assigned using density functional theory (DFT) calculations of NMR parameters for a number of structural models with a range of possible local F environments generated by F-/OH- substitution. These assignments are supported by two-dimensional 19F double-quantum MAS NMR experiments that correlate F sites based on either spatial proximity (via dipolar couplings) or through-bond connectivity (via scalar, or J, couplings). The observation of 19F-19F J couplings is unexpected as the fluorines coordinate Mg atoms and the Mg-F interaction is normally considered to be ionic in character (i.e., there is no formal F-Mg-F covalent bonding arrangement). However, DFT calculations predict significant 19F-19F J couplings, and these are in good agreement with the splittings observed in a 19F J-resolved MAS NMR experiment. The existence of these J couplings is discussed in relation to both the nature of bonding in the solid state and the occurrence of so-called "through- space" 19F-19F Jcouplings in solution. Finally, we note that we have found similar structural disorder and spin-spin interactions in both synthetic and naturally occurring clinohumite samples. [ABSTRACT FROM AUTHOR]

A disaccharide is a challenging case for high-resolution 1H solid-state NMR because of the 24 distinct protons (14 aliphatic and 10 OH) having 1H chemical shifts that all fall within a narrow range of approximately 3 to 7 ppm. High-resolution 1H (500 MHz) double-quantum (DQ) combined rotation and multiple pulse sequence (CRAMPS) solid-state NMR spectra of β-maltose monohydrate are presented. 1H–1H DQ-SQ CRAMPS spectra are presented together with 1H (DQ)–13C correlation spectra obtained with a new pulse sequence that correlates a high-resolution 1H DQ dimension with a 13C single quantum (SQ) dimension using the refocused INEPT pulse-sequence element to transfer magnetization viaone-bond 13C–1H Jcouplings. Compared to the observation of only a single broad peak in a 1H DQ spectrum recorded at 30 kHz magic-angle spinning (MAS), the use of DUMBO 1H homonuclear decoupling in the 1H DQ CRAMPS experiment allows the resolution of distinct DQ correlation peaks which, in combination with first-principles chemical shift calculations based on the GIPAW (Gauge Including Projector Augmented Waves) plane-wave pseudopotential approach, enables the assignment of the 1H resonances to the 24 distinct protons. We believe this to be the first experimental solid-state NMR determination of the hydroxyl OH 1H chemical shifts for a simple sugar. Variable-temperature 1H–1H DQ CRAMPS spectra reveal small increases in the 1H chemical shifts of the OH resonances upon decreasing the temperature from 348 K to 248 K. [ABSTRACT FROM AUTHOR]

We adapt the DFT+U method in the gauge-including projector augmented-wave NMR chemical shift calculations within the plane wave pseudopotential implementation. The nonlocal Hubbard correction potential has been reexamined in order to comply with the gauge-including projector augmented-wave transformation under an external uniform magnetic field. The resulting expression is suitable for chemical shift calculations using both norm-conserving and ultrasoft pseudopotentials in the proector augmented-wave scheme. The implementation is applied to the 17O solid-state NMR chemical shift calculations for transition-metal and rare-earth oxides, including TiO2, ZnO, Ti2O3, La2O3, and CeO2. A comparison between the DFT and DFT+U NMR chemical shifts for the selected materials is presented. [ABSTRACT FROM AUTHOR]

Heteronuclear solid-state magic-angle spinning (MAS) NMR experiments for probing 15N-17O dipolar and Jcouplings are presented for [²H(NH3),1-13C,15N,17O2]glycine··HCI and [15N2,17O2]uracil. Two-dimensional 15N-17O correlation spectra are obtained using the R³-HMQC experiment; for glycine-²HCl, the intensity of the resolved peaks for the C=O and C-O²H 17O resonances corresponds to the relative magnitude of the respective 15N-17O dipolar couplings. 17O-15N REDOR curves are presented for glycine·²HCI; fits of the initial buildup (ΔS/S < 0.2) yield effective dipolar couplings in agreement with (±20%) the root-sum-squared dipolar couplings determined from the crystal structure. Experimental 15N-17O REAPDOR curves for the 15N resonances in glycine·²HCI and uracil fit well to the universal curve presented by Goldbourt et al. (J. Am. Chem. Soc. 2003, 125, 11194). Heteronuclear 13C-17O and 15N-17O J couplings were experimentally determined from fits of the quotient of the integrated intensity obtained in a heteronuclear and a homonuclear spin-echo experiment, SQ(r) = SHET(v)/SHOM(τ). For glycine·²HCI, ¹JCO was determined as 24.7 ± 0.2 and 25.3 ± 0.3 Hz for the C=O and C-O²H resonances, respectively, while for uracil, the average of the two NHïO hydrogen-bond-mediated J couplings was determined as 5.1 ± 0.6 Hz. In addition, two-bond intramolecular J couplings, 2JOO = 8.8 ± 0.9 Hz and ²JN1,N3 = 2.7 ± 0.1 Hz, were determined for glycine·2HCI and uracil, respectively. Excellent agreement was found with J couplings calculated using the CASTEP code using geometrically optimized crystal structures for glycine·HCI [¹Jco(C=O) = 24.9 Hz, ¹Jco(C-OH) = 27.5 Hz, ²JOO = 7.9Hz] and uracil [2hJN1,O4 = 6.1 Hz, 2hJN3,O4 = 4.6 Hz, ²JN1,N3 = 2.7 Hz]. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) has been used in many fields of the physical sciences, but none so successfully as in the solid state. From its origins in condensed matter physics, it has expanded into materials science, high-pressure physics and mineralogy, solid-state chemistry and more, powering entire computational subdisciplines. Modern DFT simulation codes can calculate a vast range of structural, chemical, optical, spectroscopic, elastic, vibrational and thermodynamic phenomena. The ability to predict structure-property relationships has revolutionized experimental fields, such as vibrational and solid-state NMR spectroscopy, where it is the primary method to analyse and interpret experimental spectra. In semiconductor physics, great progress has been made in the electronic structure of bulk and defect states despite the severe challenges presented by the description of excited states. Studies are no longer restricted to known crystallographic structures. DFT is increasingly used as an exploratory tool for materials discovery and computational experiments, culminating in ex nihilo crystal structure prediction, which addresses the long-standing difficult problem of how to predict crystal structure polymorphs from nothing but a specified chemical composition. We present an overview of the capabilities of solid-state DFT simulations in all of these topics, illustrated with recent examples using the CASTEP computer program. [ABSTRACT FROM AUTHOR]

We benchmark the rSCAN and r 2 SCAN exchange-correlation functionals by comparing the Nuclear Magnetic Resonance (NMR) magnetic shieldings predicted by Density Functional Theory (DFT) to experimentally observed chemical shifts of halide and oxide inorganic compounds. Significant improvement in accuracy is achieved compared to the Generalised Gradient Approximation (GGA) at a marginally higher computational cost. When using rSCAN or r 2 SCAN, the correlation coefficient between computationally predicted and experimental values approaches the theoretically expected value of -1 while reducing the deviation, allowing more accurate and reliable spectrum assignments of complex compounds in experimental investigations.

TiO 2 has been identified as a promising electron transport layer in Si solar cells. Experiments have revealed that the Si:TiO 2 interface undergoes structural changes depending on how it was fabricated. However, less is understood about the sensitivity of electronic properties, such as band alignments, to these changes. Here, we present first-principles calculations of band alignments between Si and anatase TiO 2 , investigating different surface orientations and terminations. By calculating vacuum-level alignments, we observe a large band offset reduction of 2.5 eV for the O-terminated Si slab compared to other terminations. Furthermore, a 0.5 eV increase is found for the anatase (101) surface compared to (001). We compare the band offsets obtained through vacuum alignment with four different heterostructure models. Even though the heterostructure models contain an excess of oxygen, their offsets agree well with vacuum-level alignments using stoichiometric or H-terminated slabs, and the reduction in band offsets seen for the O-terminated Si slab is not observed. Additionally, we have investigated different exchange-correlation treatments including PBE + U, postprocessing GW corrections, and the meta-GGA rSCAN functional. We find that rSCAN provides more accurate band offsets than PBE, but further corrections are still required to achieve <0.5 eV accuracy. Overall, our study quantifies the importance of surface termination and orientation for this interface., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

A combination of charge density studies and solid state nuclear magnetic resonance (NMR) 1 J NC coupling measurements supported by periodic density functional theory (DFT) calculations is used to characterise the transition from an n-π* interaction to bond formation between a nucleophilic nitrogen atom and an electrophilic sp 2 carbon atom in a series of crystalline peri-substituted naphthalenes. As the N⋅⋅⋅C distance reduces there is a sharp decrease in the Laplacian derived from increasing charge density between the two groups at ca. N⋅⋅⋅C = 1.8 Å, with the periodic DFT calculations predicting, and heteronuclear spin-echo NMR measurements confirming, the 1 J NC couplings of ≈3-6 Hz for long C-N bonds (1.60-1.65 Å), and 1 J NC couplings of <1 Hz for N⋅⋅⋅C >2.1 Å., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A combined multinuclear solid state NMR and gauge included projected augmented wave, density functional theory (GIPAW DFT) computational approach is evaluated to determine the four heteronuclear 1J(13C,17O) couplings in solid 17O enriched naphthalaldehydic acid. Direct multi-field 17O magic angle spinning (MAS), triple quantum MAS (3QMAS) and double rotation (DOR) experiments are initially utilised to evaluate the accuracy of the DFT approximations used in the calculation of the isotropic chemical shifts (δiso), quadrupole coupling constants (CQ) and asymmetry (ηQ) parameters. These combined approaches give δiso values of 313, 200 and 66 ppm for the carbonyl (C[double bond, length as m-dash]O), ether (-O-) and hydroxyl (-OH) environments, respectively, with the corresponding measured quadrupole products (PQ) being 8.2, 9.0 and 10.6 MHz. The geometry optimised DFT structure derived using the CASTEP code gives firm agreement with the shifts observed for the ether (δiso = 223, PQ = 9.4 MHz) and hydroxyl (δiso = 62, PQ = 10.5 MHz) environments but the unoptimised experimental XRD structure has better agreement for the carbonyl group (δiso = 320, PQ = 8.3 MHz). The determined δiso and ηQ values are shown to be consistent with bond lengths closer to 1.222 Å (experimental length) rather than the geometry optimised length of 1.238 Å. The geometry optimised DFT 1J(13C,17O) coupling to the hydroxyl is calculated as 20 Hz and the couplings to the ether were calculated to be 37 (O-C[double bond, length as m-dash]O) and 32 (O-C-OH) Hz. The scalar coupling parameters for the unoptimised experimental carbonyl group predict a 1J(13C,17O) value of 28 Hz, whilst optimisation gives a value of 27 Hz. These calculated 1J(13C,17O) couplings, together with estimations of the probability of each O environment being isotopically labelled (determined by electrospray ionisation mass spectrometry) and the measured refocussable transverse dephasing (T2') behaviour, are combined to simulate the experimental decay behaviour. Good agreement between the measured and calculated decay behaviour is observed.

Weak hydrogen bonds are increasingly hypothesized to play key roles in a wide range of chemistry from catalysis to gelation to polymer structure. Here, 15 N/ 13 C spin-echo magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) experiments are applied to "view" intermolecular CH···N hydrogen bonding in two selectively labeled organic compounds, 4-[ 15 N] cyano-4'-[ 13 C 2 ] ethynylbiphenyl ( 1 ) and [ 15 N 3 , 13 C 6 ]-2,4,6-triethynyl-1,3,5-triazine ( 2 ). The synthesis of 2- 15 N 3 , 13 C 6 is reported here for the first time via a multistep procedure, where the key element is the reaction of [ 15 N 3 ]-2,4,6-trichloro-1,3,5-triazine ( 5 ) with [ 13 C 2 ]-[(trimethylsilyl)ethynyl]zinc chloride ( 8 ) to afford its immediate precursor [ 15 N 3 , 13 C 6 ]-2,4,6-tris[(trimethylsilyl)ethynyl]-1,3,5-triazine ( 9 ). Experimentally determined hydrogen-bond-mediated 2h J CN couplings (4.7 ± 0.4 Hz ( 1 ) and 4.1 ± 0.3 Hz ( 2 )) are compared with density functional theory (DFT) gauge-including projector augmented wave (GIPAW) calculations, whereby species-independent coupling values 2h K CN (29.0 × 10 19 kg m -2 s -2 A -2 ( 1 ) and 27.9 × 10 19 kg m -2 s -2 A -2 ( 2 )) quantitatively demonstrate the J couplings for these "weak" CH···N hydrogen bonds to be of a similar magnitude to those for conventionally observed NH···O hydrogen-bonding interactions in uracil ( 2h K NO : 28.1 and 36.8 × 10 19 kg m -2 s -2 A -2 ). Moreover, the GIPAW calculations show a clear correlation between increasing 2h J CN (and 3h J CN ) coupling and reducing C(H)···N and H···N hydrogen-bonding distances, with the Fermi contact term accounting for at least 98% of the isotropic 2h J CN coupling.