Search results for " Enthalpy"
showing 10 items of 31 documents
Equilibrium properties of the reaction H2⇌ 2H by classical molecular dynamics simulations
2013
We have developed a classical molecular dynamics model for the hydrogen dissociation reaction, containing two- and three-particle potentials derived by Kohen, Tully and Stillinger. Two fluid densities were investigated for a wide range of temperatures, and 11 fluid densities were considered for one temperature. We report the temperature range where the degree of reaction is significant, and also where a stable molecule dominates the population in the energy landscape. The three-particle potential, which is essential for the reaction model and seldom studied, together with the two-particle interaction lead to a large effective excluded volume diameter of the molecules in the molecular fluid.…
HEAT: High accuracy extrapolated ab initio thermochemistry.
2004
A theoretical model chemistry designed to achieve high accuracy for enthalpies of formation of atoms and small molecules is described. This approach is entirely independent of experimental data and contains no empirical scaling factors, and includes a treatment of electron correlation up to the full coupled-cluster singles, doubles, triples and quadruples approach. Energies are further augmented by anharmonic zero-point vibrational energies, a scalar relativistic correction, first-order spin-orbit coupling, and the diagonal Born-Oppenheimer correction. The accuracy of the approach is assessed by several means. Enthalpies of formation (at 0 K) calculated for a test suite of 31 atoms and mole…
Free Energy, Enthalpy and Entropy from Implicit Solvent End-Point Simulations
2018
Free energy is the key quantity to describe the thermodynamics of biological systems. In this perspective we consider the calculation of free energy, enthalpy and entropy from end-point molecular dynamics simulations. Since the enthalpy may be calculated as the ensemble average over equilibrated simulation snapshots the difficulties related to free energy calculation are ultimately related to the calculation of the entropy of the system and in particular of the solvent entropy. In the last two decades implicit solvent models have been used to circumvent the problem and to take into account solvent entropy implicitly in the solvation terms. More recently outstanding advancement in both impli…
A Solar Pond for Feeding a Thermoelectric Generator or an Organic Rankine Cycle System
2017
The world energy demand is continuously growing, which means an increase in consumption for all modern fuels or stronger effort on the development and improvement of renewable technologies. Moreover, Developing Countries claims more energy and they have often wide unutilized or unusable lands. The solar energy represents a useful opportunity for these Countries. The Solar Pond is both a solar collector and a thermal storage for long period and is suitable to use in wide sunny areas. Solar pond technology is able to supply heat for several applications requiring low-grade thermal energy or for electrical power production. In order to produce electrical energy from solar ponds it is necessary…
Metal complex-DNA binding: Insights from molecular dynamics and DFT/MM calculations.
2012
Molecular dynamics (MD) simulations, followed by density functional theory/molecular mechanics (DFT/MM) calculations, provided a detailed structure of the binding site between the cationic metallointercalator (dipyrido [3,2-a:2',3'-c]phenazine)(glycinato)copper(II), [Cu(gly)(dppz)](+), and the two dodeca-deoxynucleotide duplexes [dodeca(dG-dC)]2 and [dodeca(dA-dT)]2. Three simultaneous DNA binding types were detected in the fully optimized DFT/MM structures: 1) metal coordination through exocyclic oxygen atoms of nitrogen bases; 2) intercalation of the dppz chromophore between stacked Watson-Crick AT-AT and GC-GC bases; and 3) hydrogen bonding between the glycinato ligand and amine groups o…
Cyclooctadienine — hoch gespannte C 8 H 8 ‐Kohlenwasserstoffe
1985
Mit Hilfe der MNDO-Methode werden die energiearmsten Konformationen der vier strukturisomeren Cyclooctadienine 1–4 berechnet. Aus ihren Bildungswarmen ΔHf konnen durch Bezug zu den Cyclooctatrienen 5 und 6 die geometrischen Ringspannungen Eg abgeschatzt werden. Als experimentelle Sonde fur die Ringspannung dienen die UV-, IR (Raman)- und 13C-NMR-Spektren. Cyclooctadienynes — Highly Strained C8H8-Hydrocarbons Applying the MNDO-method the conformations with lowest energy of the isomeric cyclooctadienynes 1–4 are calculated. The geometrical ring strains Eg can be evaluated from the enthalpies of formation ΔHf in relation to the cyclooctatrienes 5 and 6. UV, IR (Raman) and 13C NMR spectra serve…
Medium enthalpy geothermal systems in carbonate reservoirs, the Western Sicily example.
2013
The multidisciplinary and integrated review of existing data (mainly acquired during oil exploration), specifically reread for geothermal purposes, and the integration with new data acquired in particular key areas, such as the Mazara Del Vallo site in the southern part of western Sicily, allowed us to better understand this -regional scale- medium-enthalpy geothermal system (with measured temperatures up to 100 °C), to reconstruct the modalities and peculiarities of fluids circulation, and to evaluate the geothermal potentialities of western Sicily. We suggest that these findings could be taken as exemplificative of the behavior of low-to medium enthalpy geothermal systems hosted in carbon…
Biophysical Characterization of Polysialic Acid—Membrane Nanosystems
2019
Polysialic acid (polySia) is a long, membrane-bound, polyanionic polymer (with the degree of polymerization, DP, up to 400) of negatively charged sialic acid monomers. Biological roles of polySia are based on its ability to modulate repulsive and attractive interactions, and its ability to modulate membrane surface charge density, pH at the membrane surface, and membrane potentials. PolySia is used in anti-bacterial and anti-cancer therapies, and in neural tissue repair. Hydrophobically-modified polySia chains can form nano-structures (micelles or liposomes) with high stability and low toxicity for drug delivery. The analysis, based on the Goldman-Hodgkin-Katz equation, of transmembrane pot…
The role of atomic static displacements in binary-alloy formation
2003
Abstract A microscopic approach to considering the influence of local atomic static displacements (LASD) on binary alloy thermodynamic properties has been developed. The explicit expression for the free energy of a disordered alloy is derived within the collective variables method. The LASD are shown to promote formation of a disordered alloy. The theory is illustrated by numerical calculations performed for alloys of the Ca–Ba system. Dependence of the alloy formation heat on temperature and concentration obtained numerically agrees perfectly with the experimental data.
Effect of type, size and deformation on the polarizability of carbon nanotubes from atomic increments
2006
The interacting induced dipole polarization model is used for the calculation of the dipole–dipole polarizability α. The method is tested with single-wall carbon nanotubes (SWNTs) as a function of nanotube radius and elliptical deformation. The results are similar to ab initio reference calculations. For the zigzag tubes, the polarizability follows a remarkably simple law. The calculations effectively differentiate among SWNTs with increasing radial deformations. The polarizability and related properties can be modified continuously and reversibly by the external radial deformation. These results suggest a technology in which mechanical deformation can control chemical properties of the car…