Density functional theory Gibbs free energy

Density functional theory has also been recently applied to several dissociative pathways of HO—ONO and its anion (ONO—0 ) in aqueous solution. For example, the Gibbs free energy for the homolysis of peroxynitrous acid (HO—ONO HO -h ONO) is calculated to be AG (aq.) = 11.1 kcalmol" , a value in good agreement with experiment (13.6 kcalmoD ). For peroxynitrite homolysis (ONO—O NO2 -b O ) the calculated AG (aq.) = 13.0 kcalmoD was obtained for ion-molecule complexes with watef ... 

Dobrowolski and co-workers reported calculations of the thermodynamic stability of the products derived from cycloaddition of vinylimine and ketene and of isocyanic acid and allene using MP2, density functional theory (DFT) (B3PW91), and Hartree-Fock (HF) methods with the 6-311+- -G basis set. Fourteen different structures were calculated for these cycloaddition reactions and the values of the free Gibbs energy showed that only 4- and 3-methylene-/3-lactams could be formed in considerable amount. 

Figure 14.11. Plots of the Gibbs free energy per unit area, AG/Ap, as a function of the distance between the two oppositely charged surfaces, L, at different ionic strengths. The results were calculated using 8r = 80, and by setting —0.16 and +0.03 C/m2 as the charge densities of the stationary and mobile phases, respectively.13 [Reprinted, with permission, from J. Stahlberg, B. Jonsson, and C. Horvath, Anal. Chem. 63, 1991, 1867-1874. Theory for Electrostatic Interaction Chromatography of Proteins . 1991 by American Chemical Society.]...

It should be noted that the SPT is not a pure molecular theory in the following sense. A molecular theory is supposed to provide, say, the Gibbs free energy as a function of T, P, N as well as of the molecular parameters of the system. Once this function is available, the density of the system can be computed from the relation p = (9/x/9 )t (with pi = G/N). The SPT utilizes the effective diameter of the solvent molecules as the only molecular parameter (which is the case for a hard-sphere fluid) and, in addition to the specification of T and P, the solvent density Pw is also used as input in the theory. The latter being a measurable quantity carries with it implicitly any other molecular properties of the system. The first application of the SPT to calculate the thermodynamics of solvation in liquids was carried out by Pierotti (1963, 1965). 

We shall not discuss the SPT in any detail. However we note that the SPT is not a pure molecular theory in the following sense. A molecular theory is supposed to provide, say, the Gibbs free energy as a function of r, P, N as well as of the molecular parameters of the system. Once this function is available, the density of the system can be computed from the... 

For calculation of the equilibrium compositions of the liquid phase either the equilibrium constants of the dissociation and polycondensation reactions have to be known or they can be computed by methods which use the approach of minimizing Gibbs free energy [200-202]. In addition, ab initio modeling techniques such as density functional theory (DFT) in combination with reactive molecular dynamic (MD) simulations could be used. Once the liquid phase system is modeled, there are in principle two options to describe the vapor-liquid equilibrium. Either equations of state (EOS) or excess Gibbs free energy models (g -models) may be used to describe the thermodynamics of the liquid... 

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