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Preamble: Part 2


Basic assumptions/warnings

  1. Depends on the BO approximation - isolates the energy purely to be dependent on the geometry of nuclei but not the electrons.
  2. A different PES exists for each electronic state of the molecule
  3. The PES only corresponds to a single molecule.
  4. by its definition it only shows potential energy… not kinetic energy
    • Total energy is conserved, so kinetic energy will increase as the potential energy decreases

Features of the PES

You already know this to death..…

  • The saddle point shows us the transition state structure not the transition state of the system

Transition Rate Constant

Equation for rate constant of transition structure, according to transition theory, where:

  • \(k =\) Rate constant
  • \(k_b =\) Boltzmann constant
  • $T = $ Temperature (K)
  • \(\Delta E =\) \(\Delta G\) (transition state - ground state) - \(\Delta E\) refers to a single molecule
  • \(R =\) Gas constant
\[ k=\bigg(\frac{k_b T}{h}\bigg)e^{\frac{-\Delta E ^\ddagger}{RT}} \]


The whole PES is not necessary for these thermochemical calculations..… How can we calculate only the stationary points?