TLDR: In this post learn how to turn FROST, which certifies Hartree–Fock energies to hundreds of digits in hours, into hfatom, a 675-line C program (with Python bindings) that gets the Hartree–Fock...

TLDR: In this post learn how to extend FROST from atoms with only \(s\) orbitals to every closed-shell atom from neon to xenon, and certify their Hartree–Fock energies as rigorous upper bounds: neo...

TLDR: In this post learn how to calculate the Hartree–Fock energy of helium to 503 significant figures and of beryllium to 501, both as rigorous upper bounds, on one core of a laptop and without a ...

Try the code yourself! Click the following button to launch an ipython notebook on Google Colab which implements every check in this post: All of the code lives in FourBodyPerimetricCode/: four...

TLDR: In this post learn how to calculate a rigorous variational upper bound on the non-relativistic ground-state energy of helium, correct to 60 significant figures, computable on your laptop! Thi...

My background is in physics and when I entered the weird and wonderful world of chemistry, I remember reading about the Hohenberg and Kohn theorem which has been floating around my head ever since....

Try the code yourself! Click the following button to launch an ipython notebook on Google Colab which implements the code developed in this post: A few years ago I remember watching a YouTube v...

If you spend enough time developing scientific software, you eventually learn that the first solution to a problem is rarely the best one. Science, and the code we write to execute it, is a continu...

This post is part of a series on Hartree-Fock theory: Restricted Hartree-Fock in 100 Lines: The original post; recommended reading before this one Unrestricted Hartree-Fock in 100 Lines: Exten...

Orbitals Are Mathematical Pick up almost any introductory chemistry textbook and you will find an orbital depicted as a tangible object: a lobed shape around an atom, a probability cloud you could...