Surface Atlas
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Stepped FCC · Wide (100) terraces

FCC(511)

Increasing the leading index to five creates wider (100)-like terraces between the ledges. FCC(511) makes the distinction between terrace sites and step sites particularly easy to see.

Plane
(511)
Layer character
Stepped · separated ledges
ASE slab builder
surface

From bulk to facet

How FCC(511) is cut

(511) plane cutting through a Face-centred cubic bulk unit cell
The coloured sheet is one translated member of the (511) plane family; translating it along its normal gives an equivalent termination.

(511)

The [511] normal lies only slightly away from [100]. The bulk cut therefore preserves broad square terraces between comparatively well-separated steps.

Bulk lattice
Face-centred cubic
Plane normal
[511]
What remains
Wide (100) terraces

The plane is drawn through the centre so high-index cuts remain legible. Its orientation is what the indices specify, not its absolute position inside one cell.

Surface geometry

Read the surface from above

surface second layer third layer

L1 is the highest atom-bearing plane, followed by L2 and L3. Support coordinates outside 0–1 are periodic images. The listed Δz describes the supporting atoms, not the marker height. In the interactive model, every numbered site is placed on the same schematic guide plane above the slab; no adsorption distance or energetic ordering is implied.

Top view of FCC(511) with numbered adsorption sites
The outlined reference cell has |a1| = 13.5074 Å, |a2| = 5.1053 Å, and γ = 79.11° for the Cu slab used in the drawing. Fractional coordinates mean r∥ = ua1 + va2.
  1. terrace ontop1-fold

    Above an atom within the broad terrace.

    (u,v) = (0.2037, 4/27)s = s₁ · support shell: mean Δz = -1.389 Å from L1

    Projection of the L3 atom at (0.2037, 4/27).

    Not named in ASE
  2. step-edge ontop1-fold

    Above a low-coordinate atom at the step edge.

    (u,v) = (1/3, 1/3)s = s₁ · support shell: mean Δz = +0.000 Å from L1

    Projection of the L1 atom at (1/3, 1/3).

    Not named in ASE
  3. lower-step ontop1-fold

    Above the exposed row below the step.

    (u,v) = (0.0185, 0.2407)s = s₁ · support shell: mean Δz = -0.695 Å from L1

    Projection of the L2 atom at (0.0185, 0.2407).

    Not named in ASE
  4. terrace bridge2-fold

    Between adjacent atoms within the terrace.

    (u,v) = (0.0185, 0.4907)s = (s₁ + s₂) / 2 · support shell: mean Δz = -0.695 Å from L1

    Periodic midpoint of L2 (0.0185, 0.2407) and L2 (0.0185, 20/27).

    Not named in ASE
  5. step bridge2-fold

    Between neighbours along the upper step.

    (u,v) = (5/6, 1/12)s = (s₁ + s₂) / 2 · support shell: mean Δz = +0.000 Å from L1

    Periodic midpoint of L1 (5/6, 1/3) and L1 (5/6, -1/6).

    Not named in ASE
  6. cross-step bridge2-fold

    Between atoms on different step levels.

    (u,v) = (0.4259, 0.287)s = (s₁ + s₂) / 2 · support shell: mean Δz = -0.347 Å from L1

    Periodic midpoint of L1 (1/3, -2/3) and L2 (14/27, -0.7593).

    Not named in ASE
  7. terrace fourfold hollow4-fold

    At a four-atom opening within the terrace.

    (u,v) = (0.2685, 0.2407)s = (Σᵢ sᵢ) / 4 · support shell: mean Δz = -0.695 Å from L1

    Least-squares centroid of the 4-atom projected shell: L2 (0.0185, 0.2407), L2 (0.0185, 20/27), L2 (14/27, 0.2407), L2 (14/27, -7/27).

    Not named in ASE
  8. step threefold pocket3-fold

    A mixed-height threefold pocket beside the step.

    (u,v) = (0.6852, 2/27)s = (Σᵢ sᵢ) / 3 · support shell: mean Δz = -0.695 Å from L1

    Least-squares centroid of the 3-atom projected shell: L1 (5/6, 1/3), L2 (14/27, 0.2407), L3 (19/27, -0.3519).

    Not named in ASE

Interactive model

Rotate the slab

Sites share a schematic display height · drag to rotate · hover for names

Building the model…

Below the top layer

Why the sites are different

Compared with (311), more terrace-like atoms fit between consecutive steps. This lets adsorption approach the (100) limit away from the ledge while remaining distinct at the edge.

Side profile of FCC(511) showing its first repeating atomic layers
Side profile showing one compact stacking repeat. The dashed line follows the macroscopic surface plane.
Layer registry of FCC(511)
Layer registry viewed from above; opacity increases towards the surface.

Cell

Geometry at a glance

The spacing is \(d_{511}=a/\sqrt{27}\); [511] is \(\cos^{-1}(5/\sqrt{27})\approx15.8^\circ\) from [100].

A site name describes the ideal starting geometry. Relaxation can move an adsorbate away from it.

Practical model

Build it with ASE

The builder creates the slab. Sites marked ASE keyword can be passed directly as a named position; ASE source marks current but inconsistently documented support. Other sites require explicit Cartesian coordinates converted from the fractional construction above.

from ase.build import bulk, surface

cu = bulk("Cu", "fcc", a=3.61, cubic=True)
slab = surface(cu, (5, 1, 1), layers=10, vacuum=10)
Things that are easy to misread
  • Averaging terrace and step adsorption into one site type.
  • Using too few lateral repeats to separate adsorbates along the ledge.