Anisotropic atom–atom potentials from X-ray charge densities: application to intermolecular interactions and lattice energies in some biological and nonlinear optical materials (original) (raw)
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Journal of Physical Chemistry B, 2000
Experimental X-ray charge densities from low-temperature data are used in the evaluation of the intermolecular interactions and lattice energies of crystals of glycylglycine, DL-histidine, and DL-proline. The X-ray analysis leads to a set of atom-centered distributed multipoles, from which electrostatic interactions are calculated. Nonempirical exp-6 atom-atom potentials are used to calculate the smaller contributions of van der Waals interactions. For comparison, parallel theoretical calculations are performed on the molecular dimers (B3LYP) and the periodic crystals (Periodic Hartree-Fock, PHF). The dimer interactions show good agreement with experimental values, except for the strongest interactions in the glycylglycine crystal. The experimental charge density results correlate well with those based on the PHF calculations, but quantitative agreement for the interaction energies is only obtained after application of a scaling factor of ∼0.76 to the PHF values. The discrepancy is attributed to the well-known overestimate of molecular polarity in the HF method, resulting from neglect of electron correlation. The agreement between lattice energies derived from the experimental charge density and theoretical values from the PHF calculations is within 10 kJ/mol for the crystals examined in this study. The study provides the basis for use of experimental electrostatic moments in molecular modeling calculations of more complex systems.
Journal of Physical Chemistry B, 2000
Experimental X-ray charge densities from low-temperature data are used in the evaluation of the intermolecular interactions and lattice energies of crystals of glycylglycine, DL-histidine, and DL-proline. The X-ray analysis leads to a set of atom-centered distributed multipoles, from which electrostatic interactions are calculated. Nonempirical exp-6 atom-atom potentials are used to calculate the smaller contributions of van der Waals interactions. For comparison, parallel theoretical calculations are performed on the molecular dimers (B3LYP) and the periodic crystals (Periodic Hartree-Fock, PHF). The dimer interactions show good agreement with experimental values, except for the strongest interactions in the glycylglycine crystal. The experimental charge density results correlate well with those based on the PHF calculations, but quantitative agreement for the interaction energies is only obtained after application of a scaling factor of ∼0.76 to the PHF values. The discrepancy is attributed to the well-known overestimate of molecular polarity in the HF method, resulting from neglect of electron correlation. The agreement between lattice energies derived from the experimental charge density and theoretical values from the PHF calculations is within 10 kJ/mol for the crystals examined in this study. The study provides the basis for use of experimental electrostatic moments in molecular modeling calculations of more complex systems.
Intermolecular potentials for some crystals of hetrocyclic compounds ccontaining nitogen
Chemical Physics Letters, 1980
Atom-atom potential parameters for N-N. N-C and N-H mteractlons m a series of crystals of heterocyclic compounds contanung mtrogen are refined. The agreement wth evpenrnent is not very satisfactory. The addrtion of electrostatic interactlons is consIdered, and shown to be Important. In the last few years, a number of papers considering potential functions, mostly of the atom-atom type, for crystals of heterocyclic compounds containmg nitrogen have been published. Reynolds [l] calculated the latticedynamic propertles of pyranne fittmg an atom-atom potential plus a rutrogen lone-pair dipole-CH bond dlpoIe term. Besnainou and Cummings [2] refined atom-atom parameters for solid pyrazine and lmldazole, the last one being hydrogen bonded. Covers [3] refined atom-atom parameters on the static propertIes of six crystals containing nitrogen; these were found by Luty and van der Avoird [4] to yield poor resuks in the calculation of lattice frequencies of tetracyanoethylene. They also refined some of the parameters to give a good agreement with existing static and dynamic data. Bougeard et al. [5,6] calculated the lattice frequencies of 1,2,4tnazole and of purine, two crystals with strong hydrogen bonds. This large amount of information, however, is quite heterog'eneous: some of the crystals considered are largely hydrogen bonded, some are ring compounds, some possess dipole moment; most refmements are based on one particular crystal and the transferabdity of the parameters is not certain. Atom-atom potential parameters for a series of chlorlnated benzene crystals [7], and for brommated benzene crystals [8] have been refiied in our laboratory. l Fellow of the Consejo Naclonal de Investigacrones Clentificas y TCcmcas.
Accurate 20 K intensity data were collected on a crystal of p-amino-p H -nitrobiphenyl [a = 24.348(1), b = 5.802 (1), c = 7.158 (1) A Ê , = = = 90 , space group Pca2 1 ] at the SUNY X3A1 beamline at the National Synchrotron Light Source, using a CCD area detector and a DISPLEX cryostat. The sharp vertical pro®le of the synchrotron beam, combined with a slight instability of the cryostat, necessitates a 9-dependent correction, made possible by a large redundancy in the data set, the average multiplicity of the measurements being 8.02. In the multipole re®nement, net atomic charges were constrained to those from a -re®nement, corresponding to a more local de®nition of the pseudoatoms in the crystal. Both localized and unrestricted re®nements show a very large (more than threefold) enhancement of the dipole moment in the solid state compared with that of the isolated molecule.
Acta Crystallographica Section A, 2000
Topological analysis of experimental and theoretical (molecular and crystal) electron densities of p-nitroaniline and p-amino-p H -nitrobiphenyl reveals considerable discrepancies between experiment and theory for the bond critical points properties. Particularly large differences occur for the positive curvature along the bond path (! 3 ). The differences become somewhat smaller when more extended basis sets and correlation effects are introduced in the theoretical calculations. The effect of the crystal matrix on the properties of bond critical points is evaluated for the p-nitroaniline molecule using the 6-21G** and 6-31G** basis sets. The differences between the isolated molecule and the molecule in the crystal are too small to explain the quantitative disagreement between the theoretical and experimental topologies reported in the literature and found in the current study. For most bonds, the observed changes in the properties of the electron density agree well for both basis sets but some discrepancies are found for changes in ! 3 for NÐH and aromatic CÐC bonds. When the theoretical densities are projected into the multipole density functions through re®nement of the theoretical structure factors, the topological properties change and differences between theory and experiment are reduced. The main origin of the observed discrepancies is attributed to the nature of the radial functions in the experimental multipole model.
Crystal Growth & Design, 2014
The lattice energy E latt of the two-component crystals (three co-crystals, a salt, and a hydrate) is evaluated using two schemes. The first one is based on the total energy of the crystal and its components computed using the solid-state density functional theory method with the plane-wave basis set. The second approach explores intermolecular energies estimated using the bond critical point parameters obtained from the Bader analysis of crystalline electron density or the pairwise potentials. The E latt values of two-component crystals are found to be lower or equal to the sum of the absolute sublimation enthalpies of the pure components. The computed energies of the supramolecular synthons vary from ∼80 to ∼30 kJ/mol and decrease in the following order: acid−amide > acid− pyridine > hydroxyl−acid > amide−amide > hydroxyl−pyridine. The contributions from different types of noncovalent interactions to the E latt value are analyzed. We found that at least 50% of the lattice energy comes from the heterosynthon and a few relatively strong H-bonds between the heterodimer and the adjacent molecules.
Crystallography Reviews, 2005
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Properties of molecular crystals by means of theory
Acta Crystallographica Section A Foundations of Crystallography, 1993
A novel quantum-chemical approach to the properties of molecular crystals has recently been developed. This Hartree–Fock-based self-consistent-crystal-field method is outlined and applied to the intramolecular torsion angle in solid hydrogen peroxide, the cold-phase structure of solid dinitrogen and the hot-phase structure of solid acetylene. The potential-energy surfaces are calculated with the assumption of perfectly ordered crystals and coherent molecular potential-energy surfaces are produced. Agreement with experiment is obtained for hydrogen peroxide. It is suggested that discrepancies between calculated and observed structures of N2(s) and C2H2(s) result from static and dynamic disorder, respectively. This interpretation is consistent with the experimentally observed intramolecular-bond shortenings in these two solids. Lattice energies in good agreement with experiment are obtained in all three cases.
Journal of Molecular Liquids, 2017
Electronic structure of para-methoxybenzylidine p-ethylaniline (MBEA), a pure nematic liquid crystal has been examined using ab-initio, HF/6-31G(d,p) and DFT B3LYP/6-31G(d,p) techniques with GAMESS program. MBEA transforms from crystal to nematic at 28 ⁰ C and nematic to isotropic phase at 57 ⁰ C. Potential Energy Surface (PES) in terms of various conformations and charge distribution analysis have been carried out. Molecular Electrostatic Potential (MEP), Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) surfaces have been scanned. Ionization potential, electron affinity, electronegativity, global hardness and softness parameters of the liquid crystal molecule have been determined. Molecular and thermodynamic properties such as total energy, dipole moment, entropy, enthalpy and Gibbs free energy have been calculated at 298.15K temperature. FTIR showed that calculated and experimental frequencies are in agreement. Stacking, side by side and end to end interactions between a molecular pair have been evaluated employing modified second order perturbation theory along with multicentred-multipole expansion technique. Results have been used to elucidate the physicochemical and liquid crystalline properties of the system.