PubMed · 3249805
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H Weatherburn. Teaching Bohr atomic theory.. https://pubmed.ncbi.nlm.nih.gov/3249805/
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An ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulation at double-zeta restricted Hartree-Fock (RHF) level was performed at an elevated temperature of 363 K (90 degrees C) to study the temperature effects on the structural and dynamical properties of a Zn(II)-water complex in aqueous solution. The first hydration shell, consisting of 6 water molecules at a mean Zn-O distance of 2.16 A, was found to remain stable also at 90 degrees C with respect to exchange processes. The flexible second shell contains, in average, approximately 27 water ligands. To fully characterize the hydration structure, several other parameters such as radial and angular distribution functions (RDF and ADF) and tilt- and theta-angle distributions were evaluated and compared to data obtained at 298 K (25 degrees C). Temperature effects on the dynamics of the Zn(II)-water complex were studied in terms of water reorientations, mean ligand residence times (MRTs), and number of ligand exchange processes. To get further insight into the solute dynamics, additional data, in particular, librational and vibrational motions of water ligands and Zn-O stretching frequencies, were calculated. The second shell is considerably influenced by the elevated temperature, as the ligands' mean residence time is shortened to 4 ps from the value of 10.5 observed at room temperature. The values of the QM/MM MD simulation were also compared to the results of a classical molecular dynamics (CMD) simulation with two- plus three-body potential performed at 90 degrees C, revealing that an accurate description of the second shell and the dynamics of the Zn(II) hydrate needs the inclusion of quantum mechanics in the description.
We propose expanding the space of variations in traditional variational calculations for the energy by considering the wave function psi to be a functional of a set of functions chi:psi=psi[chi], rather than a function. A constrained search in a subspace over all functions chi such that the functional psi[chi] satisfies a sum rule or leads to a physical observable is then performed. An upper bound to the energy is subsequently obtained by variational minimization. The rigorous construction of such a constrained-search-variational wave function functional is demonstrated.
In this paper molecular quantum similarity measures (MQSM) are used to describe molecular toxicity and to construct Quantitative Structure-Toxicity Relationships (QSTR) models. This study continues the recently described relationships between MQSM and log P values, which permits to use the theoretical MQSM as an alternative to the empirical hydrophobic parameter in QSPR studies. In addition a new type of MQSM is presented in this work: it is based on the expectation value of electron-electron repulsion energy. The molecular properties studied here, as application examples are aquatic toxicity, toxicology on Bacteria and inhibition of a macromolecule employing four different molecular sets.