A theoretical description of anisotropic chemical association and its application to hydrogen-bonded fluids

The thermodynamic and structural effects of highly anisotropic, short-ranged attraction are investigated for single- and four-site interaction models using Wertheim's multi-density graph theory of chemical association. Both models consist of associating hard spheres, where the saturable attraction sites are described by conical wells centered in the hard core and evaluated in the "sticky-spot" limit. The resulting fluids then mimic many of the directional and steric-constrained properties of hydrogen-bonded fluids. The single-site model is used to explore the effects of dimerization upon the well-known properties of a planar liquid-vapor interface. Apart from hard sphere repulsion and sticky-spot attraction, a van der Waals-like dispersion interaction is incorporated to generate the critical point. Association is treated within Wertheim's thermodynamic perturbation theory, along with classical density functional methods to determine the interfacial density profile. The direct correlation functions which carry all bonding information are derived by means of the associative Ornstein-Zernike equations with a Percus-Yevick-like closure relation. The primary effects of dimerization are manifest in system thermodynamics. Critical temperatures and densities are shifted from their non-associating values and small, non-monotonic shifts in the correlation length and surface tension are also observed. While these effects are accompanied by interface compositional changes, any influence upon the density profile seems to be subsumed by use of the proper T/T[subscript c]. The four-site, network-forming model is investigated as a prototype for the thermodynamics and structural properties of water. Bonding interactions occur between "hydrogen" and electron "lone pair" sites described in the sticky-spot limit. System properties are derived under the ideal network approximation using the same methods as for the one-site model and are found to qualitatively reproduce some thermodynamic and connectivity features characteristic of real water. Partial densities are calculated self-consistently within the theory, and most thermodynamic quantities can be written in terms of the average number of hydrogen bonds per molecule. An analytical structure factor is also derived for this model

An \emph{ab initio} method for locating characteristic potential energy minima of liquids

It is possible in principle to probe the many--atom potential surface using density functional theory (DFT). This will allow us to apply DFT to the Hamiltonian formulation of atomic motion in monatomic liquids [\textit{Phys. Rev. E} {\bf 56}, 4179 (1997)]. For a monatomic system, analysis of the potential surface is facilitated by the random and symmetric classification of potential energy valleys. Since the random valleys are numerically dominant and uniform in their macroscopic potential properties, only a few quenches are necessary to establish these properties. Here we describe an efficient technique for doing this. Quenches are done from easily generated "stochastic" configurations, in which the nuclei are distributed uniformly within a constraint limiting the closeness of approach. For metallic Na with atomic pair potential interactions, it is shown that quenches from stochastic configurations and quenches from equilibrium liquid Molecular Dynamics (MD) configurations produce statistically identical distributions of the structural potential energy. Again for metallic Na, it is shown that DFT quenches from stochastic configurations provide the parameters which calibrate the Hamiltonian. A statistical mechanical analysis shows how the underlying potential properties can be extracted from the distributions found in quenches from stochastic configurations

Incidence and Effects of Feeding Intolerance in Trauma Patients

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Liquid state properties from first principles DFT calculations: Static properties

In order to test the Vibration-Transit (V-T) theory of liquid dynamics, ab initio density functional theory (DFT) calculations of thermodynamic properties of Na and Cu are performed and compared with experimental data. The calculations are done for the crystal at T = 0 and T_m, and for the liquid at T_m. The key theoretical quantities for crystal and liquid are the structural potential and the dynamical matrix, both as function of volume. The theoretical equations are presented, as well as details of the DFT computations. The properties compared with experiment are the equilibrium volume, the isothermal bulk modulus, the internal energy and the entropy. The agreement of theory with experiment is uniformly good. Our primary conclusion is that the application of DFT to V-T theory is feasible, and the resulting liquid calculations achieve the same level of accuracy as does ab initio lattice dynamics for crystals. Moreover, given the well established reliability of DFT, the present results provide a significant confirmation of V-T theory itself.Comment: 9 pages, 3 figures, 5 tables, edited to more closely match published versio