Showing papers on "Lattice energy published in 1990"
TL;DR: In this article, the authors investigate the environmental influences on anion vacancy formation, as related to a recent hypothesis connecting oxygen substoichiometry with predictable variations in the tribological properties of rutile.
Abstract: Friction and wear tests were completed with the (001) and (110) planes of single crystal rutile (TiO 2-x ) specimens sliding against selected ceramic counterfaces, in well-defined crystallographic directions. The purpose of the experiments was to investigate the environmental influences on anion vacancy formation, as related to a recent hypothesis connecting oxygen substoichiometry with predictable variations in the tribological properties of rutile. The data were obtained with two, entirely different test machines operating at various loads, speeds, temperatures, sliding directions and durations, as well as test specimen atmospheres. The results independently confirmed the predicted, anion vacancy-controlled formation of certain low and high lattice (strain) energy crystallographic shear systems (i.e., Magneli phases) and that their generation is overwhelmingly environment-dependent. The stoichiometry-controlled lattice energy of these rutile phases influences the surface and bulk shear strength (τS) of ...
106 citations
TL;DR: The most remarkable ideas suggested by this crystal simulation are the following: the crystal potential produces a contraction of the free-ion valence radial density that works as a bonding mechanism able to describe accurately the stability and equilibrium elastic constants of simple ionic crystals.
Abstract: A new theoretical scheme appropriate for studying the electronic structure of ionic crystals is presented and applied to nine AB-type cubic lattices (A=Li,Na,K; B=H,F,Cl). The scheme, called the ab initio perturbed-ion (PI) method, is based on the theory of electronic separability and the ab initio model-potential approach of Huzinaga. In the PI method, the self-consistent-field (SCF) equations for each different lattice ion are first solved in a lattice potential that contains nuclear attraction, Coulombic, and nonlocal exchange operators, and lattice projectors enforcing the required ion-lattice orthogonality. The ionic SCF solutions are then used to compute the lattice potential, and the process is repeated until ion-lattice consistency is achieved. The lattice energy and other equilibrium properties are immediately obtained from the PI wave functions. The most remarkable ideas suggested by this crystal simulation are the following: (a) The crystal potential produces a contraction of the free-ion valence radial density, large for the anions but very small for the cations, that works as a bonding mechanism able to describe accurately the stability and equilibrium elastic constants of simple ionic crystals; (b) the PI method explains well the variation of several crystal properties with hydrostatic pressure; (c) the crystal bonding can be clearly analyzed in terms of simple cationic and anionic contributions. Moreover, the PI code may be used as an efficient source of environment-consistent ionic wave functions and energies.
97 citations
TL;DR: In this paper, the phonon density of states (DOS), lattice energy and lattice heat capacity (LHC) of an isotopically disordered anharmonic crystal were analyzed.
Abstract: Expressions are obtained for the phonon density of states (DOS), lattice energy and lattice heat capacity (LHC) of an isotopically disordered anharmonic crystal. The cubic and quartic anharmonicities are taken into account besides both the force constant changes and mass difference caused by the substitutional impurities. The method of double time thermal Green’s Function (GF) is used in the development. It is shown that in the low concentration limit the LHC depends on mass and force constant changes, cubic and quartic anharmonicities and impurity-anharmonicity interactions. At low temperatures the largest contribution is found due to the defects. It is observed that the non-diagonal terms contribute significantly in the lattice energy of isotopically disordered crystal.
60 citations
TL;DR: Using geometrical inferences from known crystal structures of aromatic hydrocarbons, some novel orthorhombic crystal structures were proposed for naphthalene, anthracene and biphenyl as mentioned in this paper.
42 citations
TL;DR: In this paper, the location of Ni{sup 2+} ions in siliceous mordenite was investigated and it was found that Ni{su 2++} does not occupy well-defined extra-framework sites but its location seems to be related to the occurrence of specific Al-O-(Si-O)-sub N}-Al sequences in the siliceou lattice.
Abstract: Lattice energy minimization calculations are performed to study the location of Ni{sup 2+} ions in siliceous mordenite. It is found that Ni{sup 2+} does not occupy well-defined extra-framework sites but that its location seems to be related to the occurrence of specific Al-O-(Si-O){sub N}-Al sequences in the siliceous lattice. This study also provides a possible explanation for the limited Ni{sup 2+} ion exchange capacity in siliceous zeolites.
39 citations
TL;DR: In this paper, potential functions comprising a sum of two-and three-body terms have been obtained that reproduce the lattice energy, lattice constant, the three elastic constants and the Raman frequency of the diamond lattices of carbon, silicon and germanium.
Abstract: Potential functions comprising a sum of two- and three-body terms have been obtained that reproduce the lattice energy, lattice constant, the three elastic constants and the Raman frequency of the diamond lattices of carbon, silicon and germanium. These potentials give the sc, bcc, fcc and hcp lattices of these elements a higher energy. The carbon potential gives a graphite lattice more stable than the diamond lattice, although the stability is overestimated. For silicon and germanium, in contrast, the graphitic structure is significantly less stable than the diamond structure.
37 citations
TL;DR: In this article, the thermal features of unbranched compounds of general formula (CnH2n+1)pNH4−p]I, with n = 0-4 and p = 1-4, were studied by thermoanalytical methods (DTA, TG, DTG and Q-TG).
34 citations
01 Sep 1990
TL;DR: In this article, the effect of Al/Si disordering over the tetrahedral sites on lattice energy and the lattice constants of the mineral sillimanite Al2SiO5 was investigated.
Abstract: Computer simulation is used to investigate the effect of Al/Si disordering over the tetrahedral sites on the lattice energy and the lattice constants of the mineral sillimanite Al2SiO5. A methodology for an atomistic assessment of the energy of the reaction 2(Si-O-Al)→(Si-O-Si)+(Al-O-Al) and its various contributions is established. This ordering energy is 0.97 eV for nearest neighbour sites in the ab-plane and 0.56 eV for those separated in the c-direction. The large difference is due to a greater constraint on the atomic relaxation in the ab-plane and shows the structural dependence of the ordering energy. Its magnitude appears to be determined by a complicated balance between Coulomb and short-range repulsive energy involving strain over many bonds, both in the ordered and disordered structures. There is also a significant interaction between second neighbour sites whereas the contribution of more distant neighbours is negligible. The lattice energies of most of the 154 configurations studied show a linear behaviour as a function of short-range order, specified by the number of Al-Al pairs. The ordering temperature Tc, estimated on the basis of a statistical mechanical model of disordering, and the calculated ordering energies are in semi-quantitative agreement with experimental values.
32 citations
32 citations
IBM1
TL;DR: L'energie totale dans la theorie des liaisons fortes est determinee au second ordre dans le rapport de la largeur de la bande de liaison a la decomposition liaison-anti-liaison.
Abstract: The total energy in tight-binding theory is obtained to second order in the ratio of the width of the bonding band to the bonding-antibonding splitting. This is the reciprocal of the expansion parameter appropriate to metals. No other important approximation on the minimal-basis, nearest-neighbor, tight-binding Hamiltonian is required for the periodic lattice. This leads to a simple theory of covalent bonding that is more accurate and much more general than bond-orbital methods. The lowest-order term is a bonding term that is a square root of a sum over neighbors performed at each atom. Writing the total bonding energy as a sum of such terms evaluated locally becomes an approximation in nonperiodic systems, but gives the total-energy estimate directly in terms of local interactions. The interesting second-order term, a chemical ``grip,'' is a sum over pairs of neighbors to each atom, depending upon the angle they subtend. A radial overlap repulsion of the form A/${\mathit{d}}^{3}$+B/${\mathit{d}}^{12}$ is added, and fitted to the observed equilibrium spacing and bulk modulus. The resulting form is used for a number of covalent systems to predict spacings and relative energies in competing structures. The bonding term always favors high coordination, but the grip, larger for small atoms and nonpolar systems, determines the tetrahedral structure for semiconductors and the graphite structure for carbon. An elastic shear constant in the tetrahedral structure is also obtained. The method generalizes directly to other systems such as transition-metal compounds and ${\mathrm{SiO}}_{2}$. It also gives directly short-ranged interatomic forces, which could be used in molecular dynamics.
20 citations
TL;DR: In this article, the free energy of solvation of normal alkanes, tetraalkylmethane and tetraalkylammonium ions in water was computed with coordinate coupling.
Abstract: A detailed implementation of the polarization energy and its derivatives into a molecular dynamics program is described. In order to examine the effect of the polarization energy on the calculated free energy differences, we have computed the free energy of solvation, with coordinate coupling, of normal alkanes, tetraalkylmethane, tetraalkylammonium ions and some closed shell ions in water. The pattern of the computed free energy change is compared with the results of our earlier simulations where the polarization energy was not included in the calculation. It is found that in the majority of the cases the polarization energy contribution to the free energy change is additive. The results of the simulations are also compared with the available experimental data.
TL;DR: In this article, the lattices of polyacetylene and polypara-phenylene were investigated and the authors found that the polyphenyl lattice energy is minimized with respect to bond lengths and bond angles as well as to the overall positions of the polymer chains.
Abstract: Calculated atomistic simulation investigations of the lattices of polyacetylene and polypara-phenylene are reported. When the lattice energy is minimized with respect to bond lengths and bond angles as well as to the overall positions of the polymer chains stable structures are found which are not revealed by rigid-chain calculations. The calculated structures for polyacetylene are consistent with the different setting angles found by different experimental groups. Polypara-phenylene shows a metastable structure which is planar, reflecting the observed tendency of the lattices of some shorter chain polyphenyls to stabilize all-planar conformations.
01 Jan 1990
TL;DR: In this paper, it was shown that the high-temperature reaction seemed to proceed more easily the lower the lattice energy of the alkaline chloride and the bare La3+ ions introduced via solid-state ion exchange.
Abstract: Highly exchanged MeI-Y (MeI = Li, Na, K, Rb, Cs) as well as La-Y zeolites were prepared through solid-state ion exchange between NH4-Y (98%) and the respective chlorides It was shown that, except for the case of Li-Y, both low- temperature and high-temperature exchange processes occurred With the system MeICl/NH4-Y the high-temperature reaction seemed to proceed more easily the lower the lattice energy of the alkaline chloride In La-Y, the bare La3+ ions introduced via solid-state ion exchange were catalytically inactive However, La-Y obtained via solid-state ion exchange was rendered an active catalyst for both ethylbenzene disproportionation and n-decane cracking after a brief contact with traces of water vapor For the solid-state reaction itself, the presence of water is not a prerequisite
TL;DR: In this article, the authors extended the technique of calculating lattice dissociation energies using static, minimum lattice energy, ionic models to allow for multiple occupancy of the ionic sites.
Abstract: The technique of calculating lattice dissociation energies using static, minimum lattice energy, ionic models has been extended to allow for multiple occupancy of the ionic sites. A particular lattice site can have a fraction x of an ionic species A and a fraction y of an ionic species B, where the position of each can be relaxed separately along with the unit cell dimensions until an equilibrium is reached. Various degrees of long and short range order can be modelled. This technique has been applied to the mineral sillimanite, Al2SiO5, to calculate the effect on the lattice energy of (Al, Si) ordering over the tetrahedral sites. It is found using this method that (Al, Si) ordering with space group Pbmn stabilizes the material by 29.25 kcal/mol (Aliv-O-Aliv), with respect to the completely disordered material.
TL;DR: In this article, the van der Waals energy minimization between NH4 and the perovskite cubo-octahedral X12 cage around it was investigated. And the authors concluded that, at temperatures above Tc, NH4 has an almost free rotation, although in some deformed crystal domains a specific NH4 rotor orientation with four N-H.. X hydrogen bonds is preferred.
TL;DR: In this paper, the authors applied the interatomic pair potential function EPEN/2 (involving exp(minus)6) plus Coulombic terms) to calculate the enthalpy of formation of NaCl {times} 2H{sub 2}O.
Abstract: The orientations and symmetries of the water molecules in the crystalline hydrates NaCl {times} 2H{sub 2}O, NaBr {times} 2H{sub 2}O, NaI {times} 2H{sub 2}O and LiI {times} 3H{sub 2}O have been investigated by use of computer modeling of the hydrates. The interatomic pair potential function EPEN/2 (involving exp({minus}6) plus Coulombic terms) was applied using previously determined parameters for the alkali-metal and halide ions and the water molecule. Rotational orientations, O-H bond lengths, and H-O-H bond angles of the water molecules were adjusted subject to symmetry constraints, using the computer program WMIN, to give structures with minimum energy. The hydrogen bonding in the modeled structures is compared with experimental evidence on the nature of the hydrogen bonding, particularly that given by infrared spectroscopy of the partially deuterated hydrates. Satisfactory agreement is found between experimental and calculated lattice energies, which provides justification for transferring the EPEN/2 parameters among the various ionic and molecular structure types. The enthalpy of formation of NaCl {times} 2H{sub 2}O is calculated from this result to be {minus}255.9 kcal/mol ({plus minus}5%); this value has not heretofore been reported.
TL;DR: The vibrational spectra of the para-and ferroelectric phases of thiourea are interpreted by a lattice-dynamical calculation using atom-atom interactions and the multipole expansion.
TL;DR: In this article, the enthalpies of the formation of gaseous 2-amino acid esters and their crystalline hydrochlorides were estimated on the basis of the Benson group additivity method and available literature information.
TL;DR: In this article, the LDA-FF algorithm was used to predict a modest intraplanar lattice expansion (dilayer: 2.8%, monolayer: 1.6%), and a substantial interplanar contraction (i.e., dilayer c/a=1.46 versus calculated bulk C/a = 1.64).
Abstract: Systematic local density treatment (via the all-electron, full-potential, linear combination of gaussian orbitals fitting function (LCGTO-FF) algorithms) of the cohesive properties of mono- and dilayer Li when combined with recent calculations for bulk Li of similar high quality, yields a prediction of modest intraplanar lattice expansion (dilayer: 2.8%, monolayer: 1.6%) and substantial interplanar contraction (dilayer c/a=1.46 versus calculated bulk c/a=1.64). The differences between these predictions and the limited experimental data for Li overlayers on graphite (which exhibit about 6.1% expansion in nearest-neighbour separation) suggest possible substrate or bonding effects in the experiment. The total dilayer cohesive energy is 79.8% of the bulk cohesive energy while for the monolayer the fraction is 63.1%. The interplanar contribution to the dilayer cohesive energy is -0.29 eV. The dilayer uniaxial (c-axis) compressibility is 2.5 times as large as the calculated value for the HCP Li crystal (the latter value is in quite good agreement with available measurements). Mono- and dilayer energy bands (at the level of bare Kohn-Sham eigenvalues) are basically consistent with those calculated self-consistently for the crystal using the same LDA model. However, calculated work function values are larger than measured crystalline values, by more than 0.6 eV, for both the mono- and dilayers.
TL;DR: In this paper, the lattice energies of ionic crystals were calculated from a computer summation of the Coulombic interaction energies, and the enthalpies of formation for these crystals were then estimated by applying the Born-Haber cycle.
TL;DR: In this article, a molecular dynamics simulation has been performed on the crystal lithium iodide, LiI, with parameters fit to thermal expansion, isothermal compressibility, lattice energy and the frequency of the transverse optical mode at the zone center.
Abstract: A molecular dynamics simulation has been performed on the crystal lithium iodide, LiI. A rigid ion potential was used with parameters fit to thermal expansion, isothermal compressibility, lattice energy and the frequency of the transverse optical mode at the zone center. The current-current correlation function has been calculated at T = 200K and 400K, and from this the absorption and dispersion have been obtained. Anharmonic broadening is observed at the higher temperature.
TL;DR: In this article, the fraction of crystal lattice energy of ammonium and methanaminium chlorides caused by electrostatic interactions has been evaluated on the basis of modified Coulomb equation for infinite number of interacting charges using available crystallographic information and estimating charge distribution for cations by MNDO and INDO methods.
Abstract: The fraction of crystal lattice energy of ammonium and methanaminium chlorides caused by electrostatic interactions has been evaluated on the basis of modified Coulomb equation for infinite number of interacting charges using available crystallographic information and estimating charge distribution for cations by MNDO and INDO methods. The evaluated characteristics compare well with experimentally derived crystal lattice energies particularly with respect to the observed trends of both quantities on the degree of substitution.
TL;DR: In this article, the interaction energy between component anion and cation of an oxide is evaluated from the lattice energy of the oxide in the Born-Haber cycle, assuming that no complex ions are formed in the slag and additivity of pairwise interaction.
Abstract: Interaction energy between component anion and cation of an oxide is evaluated from the lattice energy of the oxide. In the calculation of the lattice energy from thermal data and ionization energy of elements, the Born-Haber cycle is used. By assuming that no complex ions are formed in the slag and additivity of pairwise interaction, the interaction energy to oxide anion in a slag is expressed as the average of the lattice energy of the component oxides on the mole fraction base. The averaged lattice energy for sulfide anion in the slag is also derived by the same manner. The oxide anion in calcium oxide is chosen as the reference state in order to correlate the interaction energy with the activity coefficient of the oxide anion. The logarithmic value of the activity coefficient of oxide anion in a slag is expected to have linear relation with the averaged lattice energy obtained from the lattice energy of the component oxides. The relation is examined by the use of sulfide capacity data for several slags, where the activity coefficient of sulfide anion is also taken into account.
TL;DR: In this paper, the theory of electronic separation is applied to the calculation of the ground state total energy and related bulk properties of simple ionic crystals, based on a general equation of this theory that gives the total energy of the crystal in terms of additive energies of conjugate clusters.
TL;DR: In this paper, the lattice energy has a close relationship with the magnitude of TC, and the TC is always depressed without any exception, when the energy of lattice is decreased.
Abstract: The orthorhombic-tetragonal transition, relationship between oxygen content and TC, electronic state of Cu and TC, lattice energy and TC in YBCO and its doped systems (Cu doped by Sn, Al, Fe, Zn, N; Ba by Sr, Ca; Y by Pr,Gd,Dy, respectively.) have been studied systematically. The experiments show that the O-T transition may not be the predominant factor governing superconductivity; there is no regular relationship between superconductivity and the oxygen content. In order to fully understand superconductivity, other defects must be considered; the valence of Cu has a strong correlation with oxygen content, but has no direct relationship with the TC value. The correlation among the electronic states of Ba, Cu and O are discovered, which is helpful to know the electfonic behavior of this material. Finally, we show that the lattice energy has a close relationship with the magnitude of TC. As the lattice energy is decreased, the TC is always depressed without any exception. The authors suggest that the lattice energy may be a probable predominant factor to superconductivity.