From f7d88d0ae1c5544cc517ae6b25970f82d82b1496 Mon Sep 17 00:00:00 2001 From: Prefetch Date: Sat, 20 Feb 2021 13:35:51 +0100 Subject: Complete switch to MathJax --- content/_index.md | 6 +++--- static/know/concept/blochs-theorem/index.html | 13 +++++++++---- 2 files changed, 12 insertions(+), 7 deletions(-) diff --git a/content/_index.md b/content/_index.md index 2e49ddb..155442f 100644 --- a/content/_index.md +++ b/content/_index.md @@ -5,11 +5,11 @@ template = "home.html" Welcome to my personal website. When the stars align, I'll post something here related to my areas of interest: -open-source software, programming, optimization, server management, -mathematics, physics and sometimes even linguistics. +open-source software, server management, programming, optimization, +mathematics, physics and even linguistics. This website is served by [nginx](https://nginx.org/), and built from scratch using the awesome [Zola](https://www.getzola.org/) static generation tool. -I also aim to keep it forever free of advertising, trackers, and JavaScript, +I also aim to keep it forever free of advertising and trackers, and to maintain my A+ score for [TLS quality](https://www.ssllabs.com/ssltest/analyze.html?d=prefetch.eu). diff --git a/static/know/concept/blochs-theorem/index.html b/static/know/concept/blochs-theorem/index.html index 9710710..d900aba 100644 --- a/static/know/concept/blochs-theorem/index.html +++ b/static/know/concept/blochs-theorem/index.html @@ -5,6 +5,7 @@ Prefetch | Bloch’s theorem + - + +
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Bloch’s theorem

In quantum mechanics, Bloch’s theorem states that, given a potential \(V(\vec{r})\) which is periodic on a lattice, i.e. \(V(\vec{r}) = V(\vec{r} + \vec{a})\) for a primitive lattice vector \(\vec{a}\), then it follows that the solutions \(\psi(\vec{r})\) to the time-independent Schrödinger equation take the following form, where the function \(u(\vec{r})\) is periodic on the same lattice, i.e. \(u(\vec{r}) = u(\vec{r} + \vec{a})\):

\[ @@ -53,7 +59,7 @@ \end{aligned} \]

In other words, in a periodic potential, the solutions are simply plane waves with a periodic modulation, known as Bloch functions or Bloch states.

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This is suprisingly easy to prove: if the Hamiltonian \(\hat{H}\) is lattice-periodic, then it will commute with the unitary translation operator \(\hat{T}(\vec{a})\), i.e. \([\hat{H}, \hat{T}(\vec{a})] = 0\). Therefore \(\hat{H}\) and \(\hat{T}(\vec{a})\) must share eigenstates \(\psi(\vec{r})\):

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This is suprisingly easy to prove: if the Hamiltonian \(\hat{H}\) is lattice-periodic, then it will commute with the unitary translation operator \(\hat{T}(\vec{a})\), i.e. \(\comm{\hat{H}}{\hat{T}(\vec{a})} = 0\). Therefore \(\hat{H}\) and \(\hat{T}(\vec{a})\) must share eigenstates \(\psi(\vec{r})\):

\[ \begin{aligned} \hat{H} \:\psi(\vec{r}) = E \:\psi(\vec{r}) @@ -91,7 +97,6 @@ \end{aligned} \]

Then Bloch’s theorem follows from isolating the definition of \(u(\vec{r})\) for \(\psi(\vec{r})\).

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