chapter6(polymphyscourse)-閱讀頁(yè)
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【正文】 ightforward process to develop models that include all the material states and interactions present in the sample, and in the proper proportion. Also models that contain sufficient variety and quantity of local structures may need to be very large and unwieldy. ===== The first principle of modeling is one of simplification, though the degree of simplification varies considerably according to the aspects of polymer structure studies. Physical Models and Computational Models: The former helps scientists understand the 3D nature and spatial relationship of molecules while the latter captures essential physical features without unnecessary detail and plexity: (1) mathematically or numerically tractable。 (3) easy to set up, define, enter, and revise。dinger equation: (a) governs the motions of electrons and nuclei in atoms and molecules。 (b) number of electrons the system contains。 ., MOPAC, C540 fullerene(3) Molecular Mechanics: deals only with the nuclei, whose motion is governed by a “force field” that represents the equilibrium, timeaveraged effects of the electrons. The force filed is most monly represented in terms of chemically intuitive entities, ., bond stretching/pression, valence angle deformation, torsion or rotation abound bonds, and nonbonded interactions (van der Waals, electrostatic, Hbond).., Dreiding, Universal, COMPASS, etc.Advantage: great speed。 1700 hours of superputer time。 on a side。 1200 hrs on a parallel puter.Disadvantage: (a) not rigorously derived from first principles, but represent an approximation to the true forces acting in molec
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