Principles of Stellar Evolution

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…[400][401][402][403][404] The PBE functional, while providing accurate interaction energies, 405 underestimates the R O-O distance somewhat more, predicts larger frequency shifts 401 and its reliability is closely connected to the bond directionality. 406 For the most specific case of hydroxyl groups in ionic crystals like -Be(OH) 2 and Mg(OH) 2 it was proved 407 that B3LYP OH frequency shifts are in better agreement with experiments than those resulting from PW91 functional, which were definitely overestimated. In general, it can be safely stated that functionals based on Becke's exchange formulation provide better frequency shifts than those resulting from Perdew's one for bonds acting as H-bond donors.…”

“…As it was discussed in Sections 2 and 3, the defects remaining at the silica surface are, in principle, three-coordinated Si(3), non-bridging oxygen NBO, >Si=O and strained rings S2R, or (SiO) 2 . At ambient condition, due to the presence of moisture, the Si(3) and NBO defects can hardly survive the reaction with H 2 O (see also references in Table 6).…”

“…Exceptions to this class of structures are stishovite (vide supra) and fibrous silica 55,56 consisting of chains of edge-sharing [SiO 4 ] tetrahedra. The existence of this material is important, as it will be shown later, since two-silicon membered rings (SiO) 2 (hereafter called S2R) like those constituting the repeating unit in fibrous silica are also formed as isolated defects at the surface of amorphous silica subject to thermal temperature at T > 800K, imparting to the surface a reactive character.…”

“…1 The abundance originates from the stellar evolution of massive stars (>8 solar masses) in which Mg, Si and O nuclei are formed in large amounts from the nuclear fusion reactions. 2 If the star is more massive than 10 solar masses it will explode as a supernova inseminating the deep space with its newly-formed chemical elements. Therefore, silica based minerals in the rocky planets, like Earth, derive from the accretion of interstellar dust grains resulting from chemical reactions between the most electropositive elements and oxygen.…”

Creative Genesis

“…Nature aggregates and builds. Across this long timespan in the rapidly expanding universe, the stars are the furnaces in which all but the very lightest elements are forged, a process called nucleosynthesis (Clayton 1983). The stars run their courses and some explode as supernovae to disperse the heavier elements from their production sites throughout space.…”