Computed Geometries, Frequencies and Reaction Barriers · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Checking a computed mechanism

Science · Chemistry · ages 20-22
Name ______________________   Date ____________

  1. A structure shows exactly one imaginary frequency. What is it?

    • A minimum
    • A reactant complex
    • A transition state

  2. A structure shows no imaginary frequencies. What is it?

    • A minimum
    • A transition state
    • A broken calculation

  3. How is an activation barrier extracted?

    • By counting the atoms
    • By subtracting reactant energy from barrier-top energy
    • By deleting the corrections

  4. A bond is off by 0.15 angstrom. What do you conclude?

    • The method or structure needs review
    • Perfect agreement
    • Experiments are always wrong

  5. A computed bond differs from experiment by 0.01 angstrom. What do you say?

    • The method failed completely
    • The molecule is unknown
    • The agreement is fine

  6. A single-point energy on a poor geometry is worth reporting.

    Circle one:   True   False

  7. A quoted barrier should state which corrections were applied.

    Circle one:   True   False

  8. An optimised structure has one imaginary frequency. What is it, and what confirms it links the right minima?

    • A minimum, confirmed by counting atoms
    • A transition state, confirmed by following the path down both sides
    • A product, confirmed by its color
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Checking a computed mechanism W1-mt_pdiFjK2wPe-s1

  1. A transition state · One imaginary mode marks the top of a pass.
  2. A minimum · All-real vibrations mark a valley bottom.
  3. By subtracting reactant energy from barrier-top energy · The barrier is the climb from reactants to the top.
  4. The method or structure needs review · Tenth-scale gaps warn that something is off.
  5. The agreement is fine · Hundredth-scale gaps are normal and expected.
  6. False · Good energies on wrong coordinates mislead.
  7. True · Without named corrections the number cannot be judged.
  8. A transition state, confirmed by following the path down both sides · One imaginary mode marks the top, and the downhill path must reach both minima.
Worksheet · LightMySky