Descripción: Free-volume integrals for hole theories of liquids were calculated for some special cases by Monte Carlo numerical integration. The dependence of the free volume on the number of nearest neighbors is thus obtained. Only molecules interacting with a Lennard-Jones potential and a temperature near the critical one have been considered. The results differ considerably from those of earlier theories, where spherical symmetry was assumed. However, the introduction of vacant cells (holes) does not improve the thermodynamic functions obtained with the cell theory of Lennard-Jones and Devonshire.

Descripción: Fil:Weissmann, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: An SCF-MO-LCAO calculation for the four electrons involved in the straight hydrogen bond in ice is performed using a limited set of Slater-type orbitals. The energy of the four electrons plus the interaction between the "core potentials" is calculated as a function of the position of the proton along the line joining the oxygens. The energy of the hydrogen bond is obtained-8.2 kcal/mole-in good agreement with experiment. Electrostatic and delocalization contributions to the energy of the hydrogen bond are in excellent agreement with previous theoretical estimates. The potential energy for the motion of the proton results in a very asymmetric curve, with only one minimum. The dipole moment increases from 1.68 D for a free water molecule to 2.40 D thus confirming previous estimates.

Descripción: The potential energy for the diffusion of positive and negative defects in ice is calculated by a SCF-MOLCAO procedure. The resulting height of the potential energy barrier for positive defects is much lower than for negative ones, thus explaining qualitatively the greater mobility of the H 3O+ ions. It is also found that the potential-energy heights are very sensitive to the distance between the oxygens, the diffusion being greater when the oxygens are nearer. The results obtained suggest therefore that the diffusion of positive defects is correlated to the vibrations of the lattice.

Descripción: Fil:Guevara, J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.