Motion of Br₂ Molecules in Clathrate Cages. A Computational Study of the Dynamic Effects on Its Spectroscopic Behavior

This work looks into the spectroscopic behavior of bromine molecules trapped in clathrate cages combining different methodologies. We developed a semiempirical quantum mechanical model to incorporate through molecular dynamics trajectories, the effect movement of bromine molecules in clathrate cages has on its absorption spectra. A simple electrostatic model simulating the cage environment around bromine predicts a blue shift in the spectra, in good agreement with the experimental evidence

A mobile charge densities in harmonic oscillators (MCDHO) molecular model for numerical simulations: The water-water interaction

In this work we present a new proposal to model intermolecular interactions and use it for water molecules. The parameters of the model were fitted to reproduce the single molecule's electrostatic properties, a sample of 352 points in a refined ab initio single molecule deformation potential energy surface (PES), and the theoretical limit of the dimerization energy, -20.8 kJ/mol. The model was able to reproduce a sample of 180 additional points in the single molecule deformation PES, and 736 points in a pair-interaction surface computed at the MP2/aug-cc-pVQZ(') level with the counterpoise correction. Though the model reproduced the diagonal of the polarizability tensor, it could account for only 60% of the three-body nonadditive contributions to the interaction energies in 174 trimers computed at the MP2/6-311++(2d,2p) level with full counterpoise correction, but reproduced the four-body nonadditivities in 34 tetramers computed at the same level as the trimers. The model's predictions of the structures, energies, and dipoles of small clusters resulted in good agreement with experimental data and high quality ab initio calculations. The model also reproduced the second virial coefficient of steam at various temperatures, and the structure and thermodynamical properties of liquid water. We found that the short-range water-water interactions had a critical influence on the proper performance of the model. We also found that a model based on the proper intermolecular interactions requires the inclusion of intramolecular flexibility to be adequate. (C) 2000 American Institute of Physics. [S0021-9606(00)50847-2]

Semiempirical self-consistent polarization description of bulk water, the liquid-vapor interface, and cubic ice

We have applied an efficient electronic structure approach, the semiempirical self-consistent polarization neglect of diatomic differential overlap (SCP-NDDO) method, previously parametrized to reproduce properties of water clusters by Chang, Schenter, and Garrett J. Chem. Phys. 2008, 128, 164111] and now implemented in the CP2K package, to model ambient liquid water at 300 K (both the bulk and the liquid-vapor interface) and cubic ice at 15 and 250 K The SCP-NDDO potential retains its transferability and good performance across the full range of conditions encountered in the clusters and the bulk phases of water. In particular, we obtain good results for the density, radial distribution functions, enthalpy of vaporization, self-diffusion coefficient, molecular dipole moment distribution, and hydrogen bond populations, in comparison to experimental measurements