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A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of abinitio random structure searching (AIRSS), a density functional theory (DFT)‐based crystal structure prediction method for the high‐accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid‐state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form‐I and form‐II of aspirin. The root‐mean‐square deviation between experimental and calculated 1H chemical shifts was used to identify form‐I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs. [ABSTRACT FROM AUTHOR]

NMR chemical shifts were calculated from first principles for well defined crystalline organic solids. These density functional theory calculations were carried out within the plane-wave pseudopotential framework, in which truly extended systems are implicitly considered. The influence of motional effects was assessed by averaging over vibrational modes or over snapshots taken from ab initio molecular dynamics simulations. It is observed that the zero-point correction to chemical shifts can be significant, and that thermal effects are particularly noticeable for shielding anisotropies and for a temperature-dependent chemical shift. This study provides insight into the development of highly accurate first principles calculations of chemical shifts in solids, highlighting the role of motional effects on well defined systems. [ABSTRACT FROM AUTHOR]

We present a method for the first principles density functional calculation of relativistic all-electron nuclear magnetic resonance chemical shifts using pseudopotentials. The method is based on the gauge including projector augmented wave approach of Pickard and Mauri [Phys. Rev. B 63, 245101 (2001)]. Relativistic effects are included at the level of the scalar-relativistic zeroth-order regular approximation. The method allows chemical shifts of large, low symmetry structures containing heavy elements to be calculated efficiently. We demonstrate its success for a range of Se and Te containing molecules. [ABSTRACT FROM AUTHOR]

This article presents results of first-principles calculations of quadrupolar parameters measured by solid-state nuclear magnetic measurement (NMR) spectroscopy. Different computational methods based on density functional theory were used to calculate the quadrupolar parameters. Through a series of illustrations from different areas of solid state inorganic chemistry, it is shown how quadrupolar solid-state NMR properties can be tackled by a theoretical approach and can yield structural information. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [ABSTRACT FROM AUTHOR]

The 13C NMR chemical shifts for functionalized (7,0), (8,0), (9,0), and (10,0) single-walled carbon nanotubes (SWNTs) have been studied computationally using gauge-including projector-augmented plane-wave (GIPAW) density functional theory (DFT). The functional groups NH, NCH3, NCH2OH, and CH2NHCH2 have been considered, and different sites where covalent addition or substitution may occur have been examined. The shifts of the carbons directly attached to the group are sensitive to the bond which has been functionalized and may, therefore, be used to identify whether the group has reacted with a parallel or a diagonal CC bond. The addition of NH to a parallel bond renders the functionalized carbons formally sp³-hybridized, yielding shifts of around 44 ppm, independent of the SWNT radius. Reaction with a diagonal bond retains the formal sp² hybridization of the substituted carbons, and their shifts are slightly lower or higher than those of the unsubstituted carbon atoms. The calculated 1H NMR shifts of protons in the functional groups are also dependent upon the SWNT-group interaction. Upon decreasing the degree of functionalization for the systems where the group is added to a parallel bond, the average chemical shift of the unfunctionalized carbons approaches that of the pristine tube. At the same time, the shifts of the functionalized carbons remain independent upon the degree of functionalization. For the SWNTs where N-R attaches to a parallel bond, the average shift of the sp² carbons was found to be insensitive to the substituent R. Moreover, the shifts of the functionalized sp³ carbons, as well as of the carbons within the group itself, are independent of the SWNT radius. The results indicate that a wealth of knowledge may be obtained from the 13C NMR of functionalized SWNTs. [ABSTRACT FROM AUTHOR]

Periodic density functional theory (DFT) was used to calculate the structure of zircon (ZrSiO[sub4]) and reidite (scheelite polymorph of ZrSiO[sub4]) at pressures from 0-41 GPa. Subsequently, the [sup29]Si nuclear magnetic resonance (NMR) chemical shifts at each pressure were determined using the GIPAW method. The results show that in both zircon and reidite the chemical shifts become more negative with increasing pressure. The chemical shift of reidite is predicted by calculation to be -91.8 ppm and measured as -91.1 ppm. The results are used to interpret the previously observed systematic decrease in [sup29]Si NMR chemical shifts (increasingly negative) in the crystalline fraction of radiation-damaged zircon with increasing (z-dose. The original hypothesis that strain induced by the compression of the crystal by internal regions of damaged, amorphized material at high pressure was the origin of the shifts was disproved. An alternative source of internal pressure in the radiation-damaged crystals linked to "'stuffing" of the lattice with interstitial O or He atoms is proposed. [ABSTRACT FROM AUTHOR]

Phosphorus has received recent attention in the context of high-capacity and high-rate anodes for lithium- and sodium-ion batteries. Here, we present a first-principles structure prediction study combined with NMR calculations, which gives us insights into its lithiation/sodiation process. We report a variety of new phases found by the ab initio random structure searching (AIRSS) and the atomic species swapping methods. Of particular interest, a stable Na5P4-C2/m structure and locally stable structures found less than 10 meV/f.u. from the convex hull such as Li4P3-P212121, NaP5-Pnma, and Na4P3-Cmcm. The mechanical stability of Na5P4-C2/m and Li4P3-P212121 has been studied by first-principles phonon calculations. We have calculated average voltages, which suggest that black phosphorus (BP) can be considered as a safe anode in lithium-ion batteries due to its high lithium insertion voltage, 1.5 V; moreover, BP exhibits a relatively low theoretical volume expansion compared with other intercalation anodes, 216% (ΔV/V). We identify that specific ranges in the calculated shielding can be associated with specific ionic arrangements, results that play an important role in the interpretation of NMR spectroscopy experiments. Since the lithium-phosphides are found to be insulating even at high lithium concentrations, we show that Li-P-doped phases with aluminum have electronic states at the Fermi level suggesting that using aluminum as a dopant can improve the electrochemical performance of P anodes. [ABSTRACT FROM AUTHOR]

Abstract: The NMR parameters obtained from solid-state DFT calculations within the GIPAW approach for 17O- and 69/71Ga-sites in a range of predominantly oxide-based (group II monoxides, SrTiO3, BaZrO3, BaSnO3, BaTiO3, LaAlO3, LaGaO3, SrZrO3, MgSiO3 and Ba2In2O5), and gallate (α- and β-Ga2O3, LiGaO2, NaGaO2, GaPO4 and LaGaO3) materials are compared with experimental values, with a view to the future application of a similar approach to doped phases of interest as candidate intermediate temperature solid oxide fuel cell (ITSOFC) electrolytes. Isotropic and anisotropic chemical shift parameters, quadrupolar coupling constants, and associated asymmetries are presented and analyzed. The unusual GaO5 site occurring in LaGaGe2O7 is also fully characterised. In general, it is found that the theoretical results closely track the experimental trends, though some deviations are identified and discussed, particularly in regard to quadrupolar η Q-values. The high quality of the computed results suggests that this approach can be extended to study more complex and disordered phases. [Copyright &y& Elsevier]

Two-dimensional ¹H-13C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented. The experimental ¹H chemical shifts of the CH and CH₂ protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudo- potential approach. Further calculations show that the calculated change in the ¹H chemical shift when comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C-HߪO weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm) and both a short HߪO distance (<2.7 Å) and a CHO bond angle greater than 130° is observed, thus showing that directionality is important in C-HߪO hydrogen bonding. [ABSTRACT FROM AUTHOR]

[sup 17]O NMR parameters, both the chemical shifts and the quadrupolar parameters, are calculated for SiO[sub 2] polymorphs using density functional theory with the generalized gradient-corrected PBE functional. The gauge including projector augmented wave (GIPAW) method (Pickard, C. J.; Mauri, F. Phys. Rev. B 2001, 63, 245101) ensures the reproduction of all electron results while using computationally efficient pseudopotentials. The use of plane-waves permits fully converged calculations to be performed on structures containing 144 atoms in the unit cell, without the need to resort to the cluster approximation. The calculated NMR parameters of cristobalite, quartz, coesite, and faujasite are in excellent agreement with experimental data. This demonstrates that density functional theory is able to reproduce with high accuracy the [sup 17]O NMR parameters in SiO[sub 2] systems. This precision is used to assign the spectrum of the zeolite ferrierite. The data calculated for SiO[sub 2] are used to confirm that no simple correlation between the chemical shift and Cq NMR parameters and Si-O-Si angle exists, emphasizing the importance of predictive theories in this field. [ABSTRACT FROM AUTHOR]

An unambiguous crystallographic structure solution for the observed phases II-VI of high pressure hydrogen does not exist due to the failure of standard structural probes at extreme pressure. In this work we propose that nuclear magnetic resonance spectroscopy provides a complementary structural probe for high pressure hydrogen. We show that the best structural models available for phases II, III, and IV of high pressure hydrogen exhibit markedly distinct nuclear magnetic resonance spectra which could therefore be used to discriminate amongst them. As an example, we demonstrate how nuclear magnetic resonance spectroscopy could be used to establish whether phase III exhibits polymorphism. Our calculations also reveal a strong renormalization of the nuclear magnetic resonance response in hydrogen arising from quantum fluctuations, as well as a strong isotope effect. As the experimental techniques develop, nuclear magnetic resonance spectroscopy can be expected to become a useful complementary structural probe in high pressure experiments. [ABSTRACT FROM AUTHOR]

The article presents a study which focuses on the use of projector augmented wave (PAW) method for the calculation of nuclear magnetic resonance (NMR) parameters. It says that N. F. Ramsey has set the theoretical foundations for the calculation of NMR parameters in a series of pioneering papers in early 1950s. Moreover, the PAW transformation is working by computing the component of a certain atomic-like state in a pseudowave function.

The 29Si and 17O NMR parameters of six polymorphs of MgSiO3 were determined through a combination of high-resolution solid-state NMR and first-principles gauge including projector augmented wave (GIPAW) formalism calculations using periodic boundary conditions. MgSiO3 is an important component of the Earth's mantle that undergoes structural changes as a function of pressure and temperature. For the lower pressure polymorphs (ortho-, clino-, and protoenstatite), all oxygen species in the 17O high- resolution triple-quantum magic angle spinning (MAS) NMR spectra were resolved and assigned. These assignments differ from those tentatively suggested in previous work on the basis of empirical experimental correlations. The higher pressure polymorphs of MgSiO3 (majorite, akimotoite, and perovskite) are stabilized at pressures corresponding to the Earth's transition zone and lower mantle, with perovskite being the major constituent at depths >660 km. We present the first 17O NMR data for these materials and confirm previous 29Si work in the literature. The use of high-resolution multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments allows us to resolve distinct oxygen species, and full assignments are suggested. The six polymorphs exhibit a wide variety of structure types, providing an ideal opportunity to consider the variation of NMR parameters (both shielding and quadrupolar) with local structure, including changes in coordination number, local geometry (bond distances and angles), and bonding. For example, we find that, although there is a general correlation of increasing 17O chemical shift with increasing Si-O bond length, the shift observed also depends upon the exact coordination environment. [ABSTRACT FROM AUTHOR]

The article presents a study which determines the structure of powder crystals with the help of crystal structure prediction (CSP) and solid-state nuclear magnetic resonance (NMR). It states that study examined the chemical shifts of the high-resolution solid-state NMR which is known to be sensitive in molecular crystal structures. It adds that spectrum analysis was also used by the study to calculate the structure. It concludes that the easiest NMR parameter to measure is the isotopic shifts.