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Disordered nanoporous and “hard” carbons are widely used in batteries and supercapacitors, but their atomic structures are poorly determined. Here, we combine machine learning and DFT to obtain new atomistic insight into carbonaceous energy materials. We study structural models of porous and graphitic carbons, and Na intercalation as relevant for sodium-ion batteries. [ABSTRACT FROM AUTHOR]

The thermal motion of atoms in crystals is quantified by anisotropic displacement parameters (ADPs). Here we show that dispersion-corrected periodic density-functional theory can be used to compute accurate ADPs for transition metal carbonyls, which serve as model systems for crystalline organometallic and coordination compounds. [ABSTRACT FROM AUTHOR]

The thermal motion of atoms and functional groups is a key characteristic of any molecular crystal, and such motion derived from scattering experiments is conveniently visualised by means of thermal ellipsoids (the famous "ORTEP" drawings). Unfortunately, it is often impossible to obtain the underlying anisotropic displacement parameters (ADPs) for hydrogen atoms, due to their low X-ray scattering power, and sometimes no ADPs can be refined at all even for heavier atoms. In these cases, it would seem advantageous to estimate ADPs by first-principles techniques, and indeed such ORTEP plots have become available ab initio very recently. Here, we test this young method for a representative set of hydrogen-bonded molecular crystals: first, we study urea (CON2H4) as a well-known benchmark, then, its all-nitrogen analogue guanidine (CN3H5); finally, we move on to rubidium guanidinate (RbCN3H4) as a specimen with pronounced ionic interactions. For all three systems, ADPs have been obtained from density-functional theory (DFT) based phonon computations using the PHONOPY software. The results are compared with neutron-diffraction data as the experimental "benchmark" in this regard, and a critical discussion of experimental aspects is given. We observe excellent agreement between experiment and theory for the hydrogen-bonded systems urea and guanidine at low temperature, whereas high-temperature data for guanidine deviate visibly, and the more salt-like RbCN3H4 may suffer from a less-than-ideal description even at 12 K. Both are discussed in depth as there are possible solutions and directions for further research. Generally, the present results shine a favourable light on a future, more routine application of combined experimental/ theoretical approaches in chemical crystallography. [ABSTRACT FROM AUTHOR]

Mutually perpendicular hydrogen bonds, halogen bonds and stacking interactions are investigated in the seemingly simple crystal structure of bromomalonic aldehyde (C3H3O2Br). This combined experimental and theoretical study sheds new light on the role of electrostatic interactions in molecular crystalline networks and poses a caveat to look beyond what may be termed "chemical intuition". [ABSTRACT FROM AUTHOR]

A family of alkali-metal guanidinates (M = Na–Cs) has been reported recently, representing all-nitrogen analogues of alkali bicarbonates and containing the elusive guanidinate monoanion CN3H4−. Here, we describe the synthesis and characterisation of LiCN3H4 as the last representative of alkali guanidinates. Single crystals of LiCN3H4 were obtained using a solvothermal route in liquid ammonia, and the crystal structure was determined at 100 K using single-crystal X-ray diffraction (monoclinic, P21/c, Z = 4, a = 7.251(2) Å, b = 4.532(2) Å, c = 9.051(2) Å, β = 103.315(3)°). The structure of LiCN3H4 is reminiscent of the previously reported NaCN3H4 type in that both guanidinates contain tetrahedrally nitrogen-coordinated alkali-metal cations. The linking of these tetrahedra differs, however: they share corners in NaCN3H4 to form one-dimensionally infinite chains running through the crystal, whereas isolated, edge-sharing tetrahedra (Li2N6 motif) are found in the LiCN3H4 structure described here. Periodic density-functional theory (DFT) computations at the dispersion-corrected PBE + D2 level not only correctly reproduce the structural preferences, but also indicate that a NaCN3H4 polymorph should be viable adopting the lithium guanidinate type but much less easily so vice versa. [ABSTRACT FROM AUTHOR]

The covalent nature of short hydrogen bonds has been under debate for long. Here we show that the crystal orbital Hamilton population (COHP) bonding indicator gives new, complementary evidence of covalent hydrogen- - acceptor interactions in the molecular solid state. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate frameworks are widely thought of as being analogous to inorganic AB2 phases. We test the validity of this assumption by comparing simplified and fully atomistic machine-learning models for local environments in ZIFs. Our work addresses the central question to what extent chemical information can be "coarse-grained" in hybrid framework materials. [ABSTRACT FROM AUTHOR]

In chemical crystallography, the thermal motion of scattering centres is commonly described by anisotropic displacement parameters (ADPs). Very recently, it has been shown that ADPs are not only accessible by diffraction experiments but also via theory: this emerging approach seems promising but must be thoroughly tested. In this study, we have performed specifically tailored X-ray diffraction (XRD) experiments in fine steps between 100 and 300 K which allow detailed comparison to ab initio data from dispersion-corrected density functional theory (DFT) combined with periodic lattice-dynamics. The compound chosen for this study, crystalline pentachloropyridine (C5NCl5), is well suited for this purpose: it represents a molecular crystal without H atoms, thus posing no challenge to XRD; its solid-state structure is controlled by dispersion and halogen-bonding interactions; and the ADPs associated with the peripheral Cl atoms show strong temperature dependence. Quality criteria in direct and in reciprocal space prove that ADPs are predicted with high confidence for the temperature range between 100 and 200 K, and that several economic dispersion corrections to DFT can be reliably employed for this purpose. Within the limits we have explored here, the ab initio prediction of ADPs appears to be a facile and complementary tool, especially in those cases where diffraction data cannot provide a straightforward model for thermal motion. [ABSTRACT FROM AUTHOR]