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PM3 (chemistry)

PM3 (chemistry) is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand PM3 (chemistry) rather than just read about it. In short: PM3, or Parametric Method 3, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation.

PM3 (chemistry) — main illustration
PM3 (chemistry) — illustration

Key takeaways

  • PM3 (chemistry) belongs to chemistry; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect PM3 (chemistry) to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of PM3 (chemistry) from memory before moving on to harder problems.

Reference excerpt

PM3, or Parametric Method 3, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation. The PM3 method uses the same formalism and equations as the AM1 method. The only differences are: 1) PM3 uses two Gaussian functions for the core repulsion function, instead of the variable number used by AM1 (which uses between one and four Gaussians per element); 2) the numerical values of the parameters are different. The other differences lie in the philosophy and methodology used during the parameterization: whereas AM1 takes some of the parameter values from spectroscopical measurements, PM3 treats them as optimizable values. The method was developed by J. J. P. Stewart and first published in 1989. It is implemented in the MOPAC program (of which the older versions are public domain), along with the related RM1, AM1, MNDO and MINDO methods, and in several other programs such as Gaussian, CP2K, GAMESS (US), GAMESS (UK), PC GAMESS, Chem3D, AMPAC, ArgusLab, BOSS, and SPARTAN. The original PM3 publication included parameters for the following elements: H, C, N, O, F, Al, Si, P, S, Cl, Br, and I. The PM3 implementation in the SPARTAN program includes PM3tm with additional extensions for transition metals supporting calculations on Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt, and Gd. Many other elements, mostly metals, have been parameterized in subsequent work. A model for the PM3 calculation of lanthanide complexes, called Sparkle/PM3, was also introduced.

References Stewart, James J. P. (1989). "Optimization of parameters for semiempirical methods I. Method". J. Comput. Chem. 10 (2): 209–220. doi:10.1002/jcc.540100208. S2CID 36907984. Stewart, James J. P. (1989). "Optimization of parameters for semiempirical methods II. Applications". J. Comput. Chem. 10 (2): 221–264. doi:10.1002/jcc.540100209. S2CID 98850840. Stewart, James J. P. (1991). "Optimization of parameters for semiempirical methods. III Extension of PM3 to Be, Mg, Zn, Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, Hg, Tl, Pb, and Bi". Journal of Computational Chemistry. 12 (3): 320–341. doi:10.1002/jcc.540120306. S2CID 94913344. Stewart, James J. P. (2004). "Optimization of parameters for semiempirical methods IV: Extension of MNDO, AM1, and PM3 to more main group elements". Journal of Molecular Modeling. 10 (2): 155–64. doi:10.1007/s00894-004-0183-z. PMID 14997367. S2CID 11617476. For a recent review, Stewart, J. J. P. (1998). "PM3". Encyclopedia of Computational Chemistry. Wiley. Freire, Ricardo O.; Rocha, Gerd B.; Simas, Alfredo M. (2006). "Modeling rare earth complexes: Sparkle/PM3 parameters for thulium(III)". Chemical Physics Letters. 425 (1–3): 138–141. Bibcode:2006CPL...425..138F. doi:10.1016/j.cplett.2006.04.103.

Illustrations

PM3 (chemistry): Ball-and-stick model of the aplysin molecule, C15H19BrO. Colour code: Carbon, C: black Hydrogen, H: white Bromine, Br: red-brown Oxygen, O: red Structure calculated with Spartan Student 4.1, using the PM3 semi-empirical method.
Ball-and-stick model of the aplysin molecule, C15H19BrO. Colour code: Carbon, C: black Hydrogen, H: white Bromine, Br: red-brown Oxygen, O: red Structure calculated with Spartan Student 4.1, using the PM3 semi-empirical method.

Worked examples

Example 1 — a first encounter with PM3 (chemistry)

Start with the simplest possible case. Write down what PM3 (chemistry) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to PM3 (chemistry) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about PM3 (chemistry) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of PM3 (chemistry)

In research
PM3 (chemistry) appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses PM3 (chemistry) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
PM3 (chemistry) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Semiempirical quantum chemistry methods, so understanding it makes those chapters shorter.
In everyday life
Look for PM3 (chemistry) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study PM3 (chemistry) in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what PM3 (chemistry) means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain PM3 (chemistry) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PM3 (chemistry) in simple terms?

PM3, or Parametric Method 3, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation.

Why does PM3 (chemistry) matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study PM3 (chemistry)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on PM3 (chemistry).

Tags

  • Semiempirical quantum chemistry methods

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