computer science

PSI (computational chemistry)

PSI (computational chemistry) is a computer science 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 PSI (computational chemistry) rather than just read about it. In short: Psi is an ab initio computational chemistry package originally written by the research group of Henry F. Schaefer, III (University of Georgia).

Key takeaways

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

Reference excerpt

Psi is an ab initio computational chemistry package originally written by the research group of Henry F. Schaefer, III (University of Georgia). Utilizing Psi, one can perform a calculation on a molecular system with various kinds of methods such as Hartree-Fock, Post-Hartree–Fock electron correlation methods, and density functional theory. The program can compute energies, optimize molecular geometries, and compute vibrational frequencies. The major part of the program is written in C++, while Python API is also available, which allows users to perform complex computations or automate tasks easily. Psi4 is the latest release of the program package - it is open source, released as free under the LGPL3 through GitHub. Primary development of Psi4 is currently performed by the research groups of David Sherrill (Georgia Tech), T. Daniel Crawford (Virginia Tech), Francesco Evangelista (Emory University), and Henry F. Schaefer, III (University of Georgia), with substantial contributions by Justin Turney (University of Georgia), Andy Simmonett (NIH), and Rollin King (Bethel University). Psi4 is available on Linux releases such as Fedora and Ubuntu.

Features The basic capabilities of Psi are concentrated around the following methods of quantum chemistry:

Hartree–Fock method Density functional theory Møller–Plesset perturbation theory Coupled cluster CASSCF Multireference configuration interaction methods Symmetry-adapted perturbation theory Several methods are available for computing excited electronic states, including configuration interaction singles (CIS), the random phase approximation (RPA), time-dependent density functional theory (TD-DFT), and equation-of-motion coupled cluster (EOM-CCSD). Psi4 has introduced the density-fitting approximation in many portions of the code, leading to faster computations and reduced I/O requirements. Psi4 is the preferred quantum chemistry backend for the OpenFermion project, which seeks to perform quantum chemistry computations on quantum computers. In Psi4 1.4, the program was adapted to facilitate high-throughput workflows and can be connected to BrianQC to speed up calculations for Hartree-Fock and Density functional theory methods.

Worked examples

Example 1 — a first encounter with PSI (computational chemistry)

Start with the simplest possible case. Write down what PSI (computational chemistry) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, 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 PSI (computational 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 PSI (computational 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 PSI (computational chemistry)

In research: PSI (computational chemistry) appears in computer science 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 PSI (computational 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: PSI (computational chemistry) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemistry software for Linux, Computational chemistry software, Free chemistry software, so understanding it makes those chapters shorter.
In everyday life: Look for PSI (computational 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 PSI (computational chemistry) in 20 minutes

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

Frequently asked questions

What is PSI (computational chemistry) in simple terms?

Psi is an ab initio computational chemistry package originally written by the research group of Henry F. Schaefer, III (University of Georgia).

Why does PSI (computational chemistry) matter?

Because it connects several computer science 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 PSI (computational 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 PSI (computational chemistry).