Showing papers on "Lattice energy published in 1999"
TL;DR: The linear generalized equation described in this paper provides a further dimension to the prediction of lattice potential energies/enthalpies of ionic solids and can be utilized to predict and rationalize the thermochemistry in topical areas of synthetic inorganic chemistry as well as in emerging areas.
Abstract: The linear generalized equation described in this paper provides a further dimension to the prediction of lattice potential energies/enthalpies of ionic solids. First, it offers an alternative (and often more direct) approach to the well-established Kapustinskii equation (whose capabilities have also recently been extended by our recent provision of an extended set of thermochemical radii). Second, it makes possible the acquisition of lattice energy estimates for salts which, up until now, except for simple 1:1 salts, could not be considered because of lack of crystal structure data. We have generalized Bartlett's correlation for MX (1:1) salts, between the lattice enthalpy and the inverse cube root of the molecular (formula unit) volume, such as to render it applicable across an extended range of ionic salts for the estimation of lattice potential energies. When new salts are synthesized, acquisition of full crystal structure data is not always possible and powder data provides only minimal structural in...
583 citations
TL;DR: In this article, a genetic algorithm was used to generate plausible crystal structures from the knowledge of only the unit cell dimensions and constituent elements, and the lattice energy, based on the Born model of a solid, was minimized using a local optimiser for the more plausible candidate structures.
Abstract: A genetic algorithm has been used to generate plausible crystal structures from the knowledge of only the unit cell dimensions and constituent elements. We successfully generate 38 known binary oxides and various known ternary oxides with the Perovskite, Pyrochlore and Spinel structures, from starting configurations which include no knowledge of the atomic arrangement in the unit cell. The quality of the structures is initially assessed using a cost function which is based on the bond valence model with a number of refinements. The lattice energy, based on the Born model of a solid, is minimised using a local optimiser for the more plausible candidate structures. The method has been implemented within the computational package GULP. An extensive collection of Buckingham potential parameters for use in such simulations on metal oxides is also tabulated.
313 citations
TL;DR: In this paper, a self-consistent tabulation of more than 400 thermochemical radii for complex ions is presented, which can be used in the Kapustinskii equation to generate lattice energies and also as ion size parameters.
Abstract: Using rectilinear correlations of lattice energy with the inverse cubic root of the volume per molecule of complex salts of type MX (1:1), M2X (2:1), and MX2 (1:2) we have generated a comprehensive self-consistent tabulation of more than 400 thermochemical radii for complex ions. These radii can be used in the Kapustinskii equation to generate lattice energies and also as ion size parameters.
178 citations
TL;DR: In this article, an interatomic potential model has been developed for molecular-dynamics simulations of rutile, in which atomic charges vary dynamically according to the generalized electronegativity equalization principle.
Abstract: An interatomic potential model has been developed for molecular-dynamics simulations of TiO2 (rutile) based on the formalism of Streitz and Mintmire [J. Adhes. Sci. Technol. 8, 853 (1994)], in which atomic charges vary dynamically according to the generalized electronegativity equalization principle. The present model potential reproduces the vibrational density of states, the pressure-dependent static dielectric constants, the melting temperature, and the surface relaxation of the rutile crystal, as well as the cohesive energy, the lattice constants, and the elastic moduli. We find the physical properties of rutile are significantly affected by dynamic charge transfer between Ti and O atoms. The potential allows us to perform atomistic simulations on nanostructured TiO2 with various kinds of interfaces (surfaces, grain boundaries, dislocations, etc.).
64 citations
TL;DR: In this article, the transferability of a previously proposed intermolecular potential for nitramine crystals to reproduce the experimentally determined crystal structures (within the approximation of rigid molecules) of 51 nitro compounds was analyzed.
Abstract: We have analyzed the transferability of a previously proposed intermolecular potential for nitramine crystals to reproduce the experimentally determined crystal structures (within the approximation of rigid molecules) of 51 nitro compounds. These compounds include different types of acyclic, monocyclic, and polycyclic molecules. It is shown that this potential model accurately reproduces the experimentally determined crystallographic structures and lattice energies for the majority of these crystals. The best agreement with experimental structural and energetic data is obtained when the electrostatic charges have been determined using ab initio methods that include electron correlation effects, namely MP2 and B3LYP. The use of the electrostatic charges calculated at the Hartree−Fock level results in large differences between the predicted and the experimental values of the lattice energies. This difference can be significantly decreased by scaling the electrostatic charges with a general factor without in...
58 citations
TL;DR: In this paper, the method of Karfunkel and Gdanitz was used to predict potential polymorphs of aspirin, and the known structure, containing a nonplanar conformer was found, along with a number of other low energy structures, many of which are based on a planar conformation.
Abstract: Aspirin is only found experimentally in one crystal structure. In this article, the method of Karfunkel and Gdanitz is used to predict potential polymorphs of aspirin. The known structure, containing a nonplanar conformer is found, along with a number of other low energy structures, many of which are based on a planar conformer. Semiempirical and ab initio calculations show that the planar conformer is less stable than the experimentally known one. Force field calculations suggest that the planar conformer is more stable. The lattice energy of the experimentally known crystal structure is 1.4 kcal/mol lower than any of the potential crystal structures, even though there are a number of structures with lower total (lattice+intramolecular) energies. Conformational maps indicate that another stable conformation occurs within a few kilocalories per mole of the known structure. Polymorphs are predicted for this conformer, but it is found to pack poorly. It is proposed that routes to producing polymorphs of aspirin might be found if consideration is given to promoting the stability of the planar conformer with appropriate solvents or additives. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 262–273, 1999
47 citations
TL;DR: In this paper, the crystal chemistry and torsional profiles of three polymorphic diarylamines have been compared and contrasted, and new packing motifs based on those found in the other molecules are predicted to be more stable than those reported in the literature.
Abstract: The crystal chemistry and torsional profiles of three polymorphic diarylamines have been compared and contrasted. Although they have similar potential energy surfaces (PESs) for the main rotatable bond, the torsional distribution of the observed polymorphs differs greatly. In particular there are reported crystal structures for some but not all of the molecules at various positions on the PES, some of which are either maxima or non-stationary points on the gas phase surface. We have explained the distribution of the observed torsion values and postulated new packing motifs based on those found in the other molecules. According to lattice energy calculations, some of these ‘new polymorphs’ are predicted to be more stable than those reported in the literature.
33 citations
TL;DR: In this paper, a perturbation technique is proposed for solution of the generalized equations governing the thermal behavior of thin metal films described by a hyperbolic two-step model.
Abstract: A perturbation technique is proposed for solution of the generalized equations governing the thermal behaviour of thin metal films described by a hyperbolic two-step model. The generalized equations of this model contains diffusion terms in both the electron and lattice energy equations and assumes that incident laser radiation is absorbed by both the electron gas and solid lattice to account for the thermal behaviour of semiconducting and impure metals. A perturbation technique is utilized to eliminate the coupling between the electron and phonon energy equations when the normalized temperature difference between electrons and phonons is a small quantity, which is true in materials exhibit high coupling factors.
32 citations
TL;DR: The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as is shown by analyzing distances between atoms and by calculations of the lattice energy in dependence on the orientations of the molecules.
Abstract: The compounds tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) and tetrakis(trimethylsilyl)silane Si[Si(CH3)3]4 (TSi) have crystal structures with the molecules in a cubic closed-packed (c.c.p.) stacking. At room temperature both structures have space group Fm{\bar 3}m (Z = 4) with a = 13.5218 (1) A, V = 2472.3 (1) A3 for TSi, and a = 12.8902 (2) A, V = 2141.8 (1) A3 for TC. X-ray scattering data can be described by a molecule with approximately sixfold orientational disorder, ruling out a structure with free rotating molecules. Upon cooling, TSi exhibits a first-order phase transition at Tc = 225 K, as is characterized by a jump of the lattice parameter of Δa = 0.182 A and by an exothermal maximum in differential scanning calorimetry (DSC) with ΔH = 11.7 kJ mol−1 and ΔS = 50.0 J mol−1 K−1. The structure of the low-temperature phase is refined against X-ray powder data measured at 200 K. It has space group P213 (Z = 4), a = 13.17158 (6) A and V = 2285.15 (2) A3. The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as is shown by analyzing distances between atoms and by calculations of the lattice energy in dependence on the orientations of the molecules. TC has a phase transition at Tc1 = 268 K, with Δa1 = 0.065 A, ΔH1 = 3.63 kJ mol−1 and ΔS1 = 13.0 J mol−1 K−1. A second first-order phase transition occurs at Tc2 = 225 K, characterized by Δa2 = 0.073 A, ΔH2 = 6.9 kJ mol−1 and ΔS2 = 30.0 J mol−1 K−1. The phase transition at higher temperature has not been reported previously. New NMR experiments show a small anomaly in the temperature dependence of the peak positions in NMR to occur at Tc2. Rietveld refinements were performed for the low-temperature phase measured at T = 150 K [space group P213, lattice parameter a = 12.609 (3) A], and for the intermediate phase measured at T = 260 K [space group Pa{\bar 3}, lattice parameter a = 12.7876 (1) A]. The low-temperature phase of TC is formed isostructural to the low-temperature phase of TSi. In the intermediate phase the molecules exhibit a twofold orientational disorder.
31 citations
01 Jan 1999
31 citations
TL;DR: In this article, a theoretical study of the solid-state dimerization of C60 fullerene, which occurs under pressure through [2+2] cycloaddition of double bonds, is presented.
Abstract: We present a theoretical study of the solid-state dimerization of C60 fullerene, which occurs under pressure through [2+2] cycloaddition of double bonds. The possible crystal packings of (C60)2 molecules are calculated by minimization of the lattice energy with a bond charge intermolecular potential model proved successful in the previous C60 studies. The set of dimer lattices that were derived from the fcc lattice was used to construct the initial structures for minimization. The final structures found this way, although belonging to various space-group symmetries, retain approximately fcc arrangement of the constituting C60 cages. On the other hand, the structure obtained from the dimer motif observed in the o-dichlorobenzene solvate of (C60)2 exhibits a hcp-like C60 arrangement. The more energetically stable hcp-type dimer seems not to form due to the high potential barrier separating the fcc and hcp structures. The relative stability of the predicted structures changes significantly under pressure. So...
TL;DR: The best agreement between calculated energies and sublimation enthalpies was found in the case of Gavezzotti's force field, while significant discrepancies were found with the DREIDING force field and CVFF as mentioned in this paper.
TL;DR: The sensitivity of the inversion process to pressure can be understood in terms of the dependence of these energy terms, and the energy barrier, on interatomic spacing as discussed by the authors, which arises from the combination of a term representing the reduction in lattice energy in an inverted region and the strain energy associated with the interface between the inverted and non-inverted phases.
TL;DR: In this paper, the lattice calculations on the interaction energy of two heavy-light mesons (Q^2\bar{q}^2) are interpreted in terms of the potential of the corresponding single heavy light meson (Q
Abstract: Recent lattice calculations on the interaction energy of two heavy-light mesons (Q^2\bar{q}^2) are interpreted in terms of the potential of the corresponding single heavy-light meson (Q\bar{q}). This model leads to a large overestimate of the binding compared with the lattice data -- unless the basic Q\bar{q} potential is modified to become a four-quark potential.
TL;DR: The crystal and molecular structure of 5-azauracil, C3H3O2N3 M-r = 1 13.07 Da, was determined from X-ray diffraction data as discussed by the authors.
TL;DR: In this paper, a phase diagram of the TlNO3-RbNO3 system with details of the sub-solidus regions is presented and the properties of a mixed crystal or crystaline solid solution of Tl(1-x)RbxNO3, viz., structure, transition temperatures, melting temperature, etc., are presented and discussed.
Abstract: From measurements of the decrease in the heat (enthalpy) of transition in the solid phase by differential scanning calorimetry, the partial molar heats of solution at infinite dilution, χ, and the heats of solution or substitution, ΔHs°, of Tl+ in RbNO3 crystal and Rb+ in TlNO3 crystal along with their recovered lattice energies, ΔHL°, are reported. The complete phase diagram of the TlNO3–RbNO3 system with details of the sub-solidus regions is reported. The properties of a “mixed crystal’' or “crystalline solid solution’' of Tl(1-x)RbxNO3, viz., structure, transition temperatures, melting temperature, etc., are presented and discussed.
TL;DR: In this paper, a monoclinic, space group C2/c with crystal parameters of a=2.1229(3) nm, b=0.6261(8) nm.
Abstract: [Cd(NTO)4Cd(H2O)6]·4H2O was prepared by mixing the aqueous solution of 3-nitro-1,2,4-triazol-5-one and cadmium carbonate in excess. The single crystal structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group C2/c with crystal parameters of a=2.1229(3) nm, b=0.6261(8) nm, c=2.1165(3) nm, β=90.602(7)°, V=2.977(6) nm3, Z=4, Dc=2.055 g·cm−3, μ=15.45 cm−1, F(000)=1824, λ(MoKα)=0.071073 nm. The final R is 0.0282. Based on the results of thermal analysis, the thermal decomposition mechanism of [Cd(NTO)4Cd(H2O)6]·4H2O was derived. From measurements of the enthalpy of solution of [Cd(NTO)4Cd(H2O)6]·4H2O in water at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard enthalpy of dehydration have been determined as -(1747.8±4.8), -2394, -2414 and 313.6 kJ mol−1 respectively.
TL;DR: In this article, the relationship between local symmetries and polarization energy and its variation with pressure was investigated in the case of PbFI and it was shown that with an increase in pressure the ion I moves in the cell which becomes more regular.
TL;DR: In this article, the influence of intercalation on the lattice energy and configuration entropy of a Li x Mn 2 O 4 crystal is discussed, and the change of the Gibbs free energy has been calculated on the basis of statistical thermodynamics and the Born-Haber cycle.
TL;DR: In this article, an estimate of the repulsion?dispersion potentials for the oxyboryl group was made using the overlap model and Slater?Kirkwood formula, combined with empirical hydrocarbon atom?atom potentials and a distributed multipole electrostatic model.
Abstract: In order to predict the crystal structure of 2-(2-phenylethenyl)-1,3,2-benzodioxaborole (1), an estimate of the repulsion?dispersion potentials for the oxyboryl group was made using the overlap model and Slater?Kirkwood formula. This potential was combined with empirical hydrocarbon atom?atom potentials and a distributed multipole electrostatic model. This 'estimated' potential proved satisfactory in modelling the intermolecular forces that determine the crystal packing. Searches for minima in the lattice energy show that the adopted conformation optimises the lattice energy, emphasising the need for carefully balanced inter- and intramolecular potentials for predicting the crystal structures of flexible molecules. The overlap model approach to the derivation of repulsion parameters from the charge density of a benzodioxoboryl derivative was further developed to give a completely non-empirical model potential for 1. This potential could reproduce the crystal structure satisfactorily. Hence, this overlap approach shows promise as a general method of deriving repulsion potentials for a specific molecule, without recourse to experimental data or assuming transferability or combining rules for atom?atom potentials.
TL;DR: In this article, it was shown that a literature proposal to treat melting temperatures Tm similarly is in error (requiring instead an empirical fractional exponent for d), as is a similar treatment of surface tensions at Tm, where surface-phase ion pairs can account for the observed scaling exponent.
TL;DR: In this paper, a single crystal of lead salt of 3-nitro-1,2,4-triazol-5-one (NTO), [Pb(NTO)2(H2O)] was prepared and its structure was determined by a four-circle X-ray diffractometer.
Abstract: The single crystal of lead salt of 3-nitro-1,2,4-triazol-5-one (NTO), [Pb(NTO)2(H2O)] was prepared and its structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, its space group is P21/n with crystal parameters of a=0.7262(1) nm, b=1.2129(2) nm, c=1.2268(3) nm, β=90.38(2)°, V=1.0806(2) nm3, Z=4, Dc=2.97 g cm−3, µ=157.83cm−1, F(000)=888. The final R is 0.027. By using SCF-PM3-MO method we obtained optimized geometry for [Pb(NTO)2⋅H2O] and particularly positions for hydrogen atoms. Through the analyses of MO levels and bond orders it is found that Pb atom bond to ligands mainly with its 6pz and 6py AOs. The thermal decomposition experiments are elucidated when [Pb(NTO)2⋅H2O] is heated, ligand water is dissociated first and NO2 group has priority of leaving. Based on the thermal analysis, the thermal decomposition mechanism of [Pb(NTO)2⋅H2O] has been derived. The lattice enthalpy and its lattice energy were also estimated.
TL;DR: The complete set of non-vanishing third-order elastic moduli of high temperature superconductor Bi 2 Sr 2 CaCu 2 O 8 (Bi-2:2:1:2) is obtained theoretically.
TL;DR: In this article, a discussion of the structure and the ligand-field splitting parameter 10Dq for some d1 titanium (III) halides is presented, based on an ionic model allowing for the inclusion both of electrostatic and of non-Coulombic repulsive contributions.
Abstract: We present a discussion of the structure and the ligand‐field splitting parameter 10Dq for some d1 titanium (III) halides. Our approach is based on an ionic model allowing for the inclusion both of electrostatic and of non‐Coulombic repulsive contributions. The point‐Coulombic forces are treated exactly using the Madelung constant for each specific crystal. Only the metal–ligand and ligand–ligand short‐range repulsions are taken to be of importance, and are calculated using the electron‐gas model. Our results show that for the chloride the model is poor and hence that covalency is essential for understanding the heavier halides. For the fluoride systems, however, we obtain values for the bond distances, and the lattice energy for the trifluoride, which are accurate within five per cent of experiment. As previous approaches have shown, we find the negative sign for 10Dq when only the purely electrostatic interaction is included. We show in addition that overlap repulsion provides the major part of the bala...
TL;DR: The coverage-dependent binding energy of interacting dimers is investigated using the lattice gas model and the grand partition function is derived by using the Bethe approximation.
Abstract: The coverage-dependent binding energy of interacting dimers is investigated using the lattice gas model. Dimers with distinguishable ends are assumed to interact if they occupy only nearest-neighbor lattice sites. The interaction energy between a pair of dimers will be repulsive if identical ends are in nearest-neighbor positions and attractive if they are not. The grand partition function is derived by using the Bethe approximation. The energy of the system of interacting dimers is evaluated as a function of the lattice coverage at different temperatures and pair interaction potentials. Under the same conditions the average number of all types of nearest-neighbors is evaluated.
TL;DR: In this paper, a new value for the lattice energy of a-glycine was determined by combination of the experimentally measured heat of sublimation taken from literature and the quantum-chemically calculated energy difference.
Abstract: A new value for the lattice energy of a-glycine was determined by combination of the experimentally measured heat of sublimation taken from literature and the quantum-chemically calculated energy difference Etot,gp - Etot,cry, where Etot,gp is the total energy of the most stable form of the compound in the gas phase (carboxylic acid) and Etot,cry the total energy of the molecule as it occurs in its crystalline form (betaine). At the highest levels of ab initio theory employed in this study this energy difference is -(28±2) kcal/mol, indicating that older work overestimated this difference significantly. The reason for the overestimation of this energy difference was determined by means of additional ab initio calculations. The lattice energy of -(67±2)kcal/mol obtained using the new value for Etot,gp - Etot,cry is significantly more positive than an older value of -103 kcal/mol frequently cited in the literature.
TL;DR: In this article, the Verwey transition in magnetite has been analyzed by a consistent analysis of the statistical properties of an array of quantum states associated with ferrous or ferric ions in octahedrally coordinated interstices of the spinel lattice.
TL;DR: In this article, the properties of dialkylammonium halides of the general formula (C n H 2 n +1 ) 2 NH 2 ]X, where X =Br, I and n =3 or 4, were analyzed by the methods of thermoanalysis (TG, DTG, DTA, DSC).
Journal Article•
TL;DR: In this article, a model of the structure of the low-temperature orthorhombic phase (O') of LaMnO 3 was constructed using pair potentials with explicitly allowing for the many-body Jahn-Teller contribution to the crystal energy.
Abstract: A model of the structure of the low-temperature orthorhombic phase (O') of LaMnO 3 was constructed using pair potentials with explicitly allowing for the many-body Jahn-Teller contribution to the crystal energy. Microscopic factors that cause the structural instability of the LaMnO 3 lattice against rotations of oxygen octahedra and Jahn-Teller distortions were studied. Elastic and dielectric constants of the crystal in the O' phase and in phases distorted by the Jahn-Teller effect, as well as the frequencies of fundamental vibration modes, were calculated.
TL;DR: In this article, a theoretical method for calculating excess energy values (H EX or G EX ) of calcite-structure solid solutions has been devised by extending the lattice energy calculation technique for pure carbonate minerals.