Lattice energy minimization calculations

Results of Lattice Energy Minimization Calculations. Relative lattice energies of faujasite, mordenite, silicalite and sodalite were compared. For the framework and cation positions of faujasite and sodalite the same data were used as before, from Hseu (18) and Olson (19), and Baerlocher (20) and Chao (21), respectively. For mordenite and sodalite the data of Meier (22) and Mortier (23 ) (on mordenite) and Baerlocher and Meier (24) (on sodalite) were used. 

There have been many other examples of the introduction of pressure into static lattice energy minimization calculations, particularly for silicates. For example, there has been a detailed study of the effect of pressure on a-quartz using a range of different models (de Boer et al. 1996). Beyond the consideration of structural trends, this work also evaluated the pressure dependence of some physical properties as well. In particular... 

MC simulation and lattice energy minimization calculations are used to generate trial packing structures. This methodology is illustrated using the case study of tolbutamide, an antidiabetic drug. 

As molecular packing calculations involve just simple lattice energy minimizations another set of tests have focused on the finite temperature effects. For this purpose, Sorescu et al. [112] have performed isothermal-isobaric Monte Carlo and molecular dynamics simulations in the temperature range 4.2-325 K, at ambient pressure. It was found that the calculated crystal structures at 300 K were in outstanding agreement with experiment within 2% for lattice dimensions and almost no rotational and translational disorder of the molecules in the unit cell. Moreover, the space group symmetry was maintained throughout the simulations. Finally, the calculated expansion coefficients were determined to be in reasonable accord with experiment. 

Numerous organic species are known to lead to the crystallization of the MFI-type structure (7). but the tetrapropylammonium cations can be considered to be the most specific. To our knowledge no thermodynamic data such as standard formation enthalpies (AfH°) and stabilization energies attributed to the organic species have been published to corroborate this experimental observation. The published thermodynamic data (AfG°, AfH°, AfS°. Cp) are for natural zeolites (8-11) or for organic-free synthetic zeolites. However. some data have been obtained by calculations using lattice energy minimization and extended Hiickel theory (1 2) or by semi-empirical methods based on addition of the thermodynamic functions of the oxide compo-... 

Schmidt and Englert developed a method called CRYSCA (Crystal Structure Calculation) based on rigid body lattice energy minimization of ran-... 

Winkler, B., Dove, M.T.,and Leslie, M. (1991) Static lattice energy minimization and lattice dynamics calculations on alumino-silicate minerals. Am. Mineral. 76, 313-331. 

In practice, completely rigid molecule CSP is becoming less and less common some degree of molecular flexibility is now almost always included at some stage of the calculations, either in generating trial structures or in their lattice energy minimization. However, the adaptation of methods to large, very flexible molecules has been slow. 

The main alternative approach to force field methods that has emerged in the past few years is the application of solid-state (periodic) DFT calculations for the lattice energy minimization and energetic evaluation of predicted crystal structures. The main weakness of DFT is its failure to account for the attractive dispersion interactions between... 

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