dft-jacobs-ladder.typ

#import "@preview/cetz:0.3.2": canvas, draw

#set page(width: auto, height: auto, margin: 8pt)

#canvas({
  import draw: line, content, rect, circle

  let rung-sep = 2 // Vertical separation between rungs
  let width = 8.4 // Width of each rung
  let height = 1 // Height of each rung
  let circle-r = 0.8 // Radius of symbol circles
  let circle-offset = -3.2 // X offset for symbol circles

  // Helper to draw a rung with its symbol
  let draw-rung(y, color, text-content, symbol) = {
    // Draw rung rectangle
    rect(
      (-width / 2, y),
      (width / 2, y + height),
      fill: color,
      stroke: rgb("888") + 0.4pt,
    )

    // Add text content, left-aligned relative to circle and vertically centered
    content(
      (circle-offset + circle-r + 0.2, y + height / 2),
      text(size: 10pt)[#align(horizon)[#text-content]],
      anchor: "west", // Left align text
    )

    // Add symbol circle if provided
    if symbol != none {
      circle(
        (circle-offset, y + height / 2),
        radius: circle-r,
        fill: color,
        stroke: rgb("888") + 0.4pt,
      )
      content(
        (circle-offset, y + height / 2),
        align(center)[#symbol],
      )
    }
  }

  // Draw all rungs from bottom to top
  draw-rung(0, rgb("b4a7d6"), [0: *Hartree World*], none)

  draw-rung(rung-sep, rgb("a4c2f4"), [1: *Local Density Approx. (LDA)*\ VWN, GPW92], $rho(bold(r))$)

  draw-rung(
    2 * rung-sep,
    rgb("f9cb9c"),
    [2: *Generalized Gradient Approx. (GGA)*\ PBE, BLYP],
    $nabla rho(bold(r))$,
  )

  draw-rung(3 * rung-sep, rgb("ffe599"), [3: *Meta-GGA*\ (r/r$""^2$)SCAN], [$\ nabla^2rho(bold(r))$ \ $tau(bold(r))$])

  draw-rung(
    4 * rung-sep,
    rgb("b6d7a8"),
    [4: *Occupied Hybrid Methods* \ B3LYP, CAM-B3LYP, M06-2X],
    ${phi_i^"occ"}$,
  )

  draw-rung(5 * rung-sep, rgb("ea9999"), [5: *Virtual Double-Hybrids* \ B2PLYP], ${phi_i^"virt"}$)

  draw-rung(6 * rung-sep, rgb("ffb7c5"), [*Chemical accuracy*], none)

  // Draw vertical lines connecting rungs
  line(
    (-width / 2, 0),
    (-width / 2, 6 * rung-sep + height),
    stroke: 0.7pt,
  )
  line(
    (width / 2, 0),
    (width / 2, 6 * rung-sep + height),
    stroke: 0.7pt,
  )
})