OPLS

Key takeaways

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

Reference excerpt

The OPLS (Optimized Potentials for Liquid Simulations) force field was developed by Prof. William L. Jorgensen at Purdue University and later at Yale University, and is being further developed commercially by Schrödinger, Inc.

Functional form

The functional form of the OPLS force field is very similar to that of AMBER:

E ( r N ) = E b o n d s + E a n g l e s + E d i h e d r a l s + E n o n b o n d e d {\displaystyle E\left(r^{N}\right)=E_{\mathrm {bonds} }+E_{\mathrm {angles} }+E_{\mathrm {dihedrals} }+E_{\mathrm {nonbonded} }}

E b o n d s = ∑ b o n d s K r ( r − r 0 ) 2 {\displaystyle E_{\mathrm {bonds} }=\sum _{\mathrm {bonds} }K_{r}(r-r_{0})^{2}\,}

E a n g l e s = ∑ a n g l e s k θ ( θ − θ 0 ) 2 {\displaystyle E_{\mathrm {angles} }=\sum _{\mathrm {angles} }k_{\theta }(\theta -\theta _{0})^{2}\,}

E d i h e d r a l s = ∑ d i h e d r a l s ( V 1 2 [ 1 + cos ⁡ ( ϕ − ϕ 1 ) ] + V 2 2 [ 1 − cos ⁡ ( 2 ϕ − ϕ 2 ) ] + V 3 2 [ 1 + cos ⁡ ( 3 ϕ − ϕ 3 ) ] + V 4 2 [ 1 − cos ⁡ ( 4 ϕ − ϕ 4 ) ] ) {\displaystyle E_{\mathrm {dihedrals} }=\sum _{\mathrm {dihedrals} }\left({\frac {V_{1}}{2}}\left[1+\cos(\phi -\phi _{1})\right]+{\frac {V_{2}}{2}}\left[1-\cos(2\phi -\phi _{2})\right]+{\frac {V_{3}}{2}}\left[1+\cos(3\phi -\phi _{3})\right]+{\frac {V_{4}}{2}}\left[1-\cos(4\phi -\phi _{4})\right]\right)}

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with OPLS

Start with the simplest possible case. Write down what OPLS 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 OPLS 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 OPLS 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 OPLS

In research: OPLS 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 OPLS 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: OPLS is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computational chemistry, Computational chemistry stubs, Force fields (chemistry), so understanding it makes those chapters shorter.
In everyday life: Look for OPLS 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.

How to study OPLS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OPLS 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 OPLS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OPLS in simple terms?

The OPLS (Optimized Potentials for Liquid Simulations) force field was developed by Prof. William L.

Why does OPLS 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 OPLS?

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 OPLS.