physics

MNDO

MNDO is a physics 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 MNDO rather than just read about it. In short: MNDO, or Modified Neglect of Diatomic Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Diatomic Differential Overlap integral approximation.

Key takeaways

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

Reference excerpt

MNDO, or Modified Neglect of Diatomic Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Diatomic Differential Overlap integral approximation. Similarly, this method replaced the earlier MINDO method. It is part of the MOPAC program and was developed in the group of Michael Dewar. It is also part of the AMPAC, GAMESS (US), PC GAMESS, GAMESS (UK), Gaussian, ORCA and CP2K programs. Later, it was essentially replaced by two new methods, PM3 and AM1, which are similar but have different parameterisation methods. The extension by W. Thiel's group, called MNDO/d, which adds d functions, is widely used for organometallic compounds. It is included in GAMESS (UK). MNDOC, also from W. Thiel's group, explicitly adds correlation effects though second order perturbation theory with the parameters fitted to experiment from the correlated calculation. In this way, the method should give better results for systems where correlation is particularly important and different from that in the ground state molecules from the MNDO training set. This includes excited states and transition states. However, Cramer argues that "the model has not been compared to other NDDO models to the extent required to assess whether the formalism fulfills its potential."

References

MNDO Dewar, Michael J. S.; Thiel, Walter (1977). "Ground states of molecules. 38. The MNDO method. Approximations and parameters". Journal of the American Chemical Society. 99 (15): 4899. doi:10.1021/ja00457a004.

MNDO/d Thiel, Walter; Voityuk, Alexander A. (1996). "Extension of MNDO to d Orbitals: Parameters and Results for the Second-Row Elements and for the Zinc Group". Journal of Physical Chemistry. 100 (2): 616. doi:10.1021/jp952148o. hdl:11858/00-001M-0000-0027-C145-2. Thiel, Walter (1996). "Perspectives on Semiempirical Molecular Orbital Theory". Advances in Chemical Physics. Advances in Chemical Physics. Vol. 93. pp. 703–757. doi:10.1002/9780470141526.ch10. ISBN 978-0-470-14152-6.

MNDOC Cramer, C. J. (2002). Essentials of Computational Chemistry. John Wiley. p. 135. Thiel, Walter (1981). "The MNDOC method, a correlated version of the MNDO model". Journal of the American Chemical Society. 103 (6): 1413–1420. doi:10.1021/ja00396a021. Thiel, Walter (1981). "MNDOC study of reactive intermediates and transition states". Journal of the American Chemical Society. 103 (6): 1420–1425. doi:10.1021/ja00396a022. Schweig, Armin; Thiel, Walter (1981). "MNDOC study of excited states". Journal of the American Chemical Society. 103 (6): 1425. doi:10.1021/ja00396a023.

Worked examples

Example 1 — a first encounter with MNDO

Start with the simplest possible case. Write down what MNDO claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 MNDO 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 MNDO 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 MNDO

In research: MNDO appears in physics 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 MNDO 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: MNDO 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 MNDO 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 MNDO in 20 minutes

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

Frequently asked questions

What is MNDO in simple terms?

Why does MNDO matter?

Because it connects several physics 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 MNDO?

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 MNDO.