CEM 888: Molecular Modeling: Applications for Experimentalists What can theory do for the practicing chemist? What do we wish it could do? A brief progress report with examples on the performance and practical utility of theoretical tools for non-theoreticians The Evolving Roles of Theory
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What can theory do for the practicing chemist? What do we wish it could do? A brief progress report with examples on the performance and practical utility of theoretical tools for non-theoreticians
Zeroth order wishes:
• How are stationary points and reaction path defined?
• Are they unique and independent of coordinate system?
• What is a “Reaction Coordinate” anyway, in 3n-6 dimensions?
• In gas phase, two fragments always “stick” together a bit.
• TS may be above or below fragment totals.
• Minima may have inverse E order e.g. H3O–
Vibrations in the TS for the (degenerate) SN2 attack of Cl– on CH3Cl. Note: all but the Reaction Coord motion are positive “ordinary” vibrations
From Anwar G. Baboul and H. Bernhard Schlegel, “Improved method for calculating projected frequencies along a reaction path” J. Chem. Phys.1997, 107, 9413-9417.
Figure 9. The Müller-Brown potential surface. Dashed line, energy contours. Solid line is the reduced potential surface defined as gx0, gy=0. The black circles are the stationary points, minimum, M1 and M2, transition state, TS1. The empty circles are the starting point, P, and the turning point, TP. The black dots are the different points evaluated by the algorithm; see text for more details.