This simulator builds the conventional unit cell of silicon in 3D so you can see the diamond-cubic arrangement that underlies every silicon chip. Rotate the crystal, highlight a tagged atom's four nearest neighbors, vary the lattice parameter and read the geometry and density that follow from it.
• A 3D lattice of silicon sites, tetrahedral covalent bonds, the conventional cubic cell, a selected atom with its coordination and an optional atomic-vibration overlay. • Controls for lattice parameter (0.52-0.57 nm), illustrative vibration amplitude (0-0.12 of bond length), crystal rotation and nearest-neighbor bond display. • Readouts for nearest-neighbor spacing, tetrahedral bond angle, effective atoms per unit cell, atomic density and mass density. • Experiments for the reference cell (spacing about 0.2352 nm and density about 2.329 g/cm³) and for observing vibration without changing the equilibrium spacing.
In the diamond-cubic cell each atom bonds to four neighbors at the corners of a tetrahedron. The nearest-neighbor spacing is d = √3 a / 4, the bond angle is acos(-1/3) ≈ 109.47°, and the cell holds 8×⅛ + 6×½ + 4 = 8 atoms. That gives an atomic density N = 8/a³ and a mass density ρ = N × 28.0855 / NA. Changing the lattice parameter rescales all of these together.
The lattice parameter is an editable geometric input, not a thermal-expansion model. Spheres and bonds are illustrative, and the vibration overlay is a bounded teaching effect rather than a phonon or electronic-structure calculation.
It is a face-centered cubic lattice with a two-atom basis, in which every atom bonds to four neighbors arranged at the corners of a tetrahedron. Silicon, germanium and diamond share this structure.
Four equivalent bonds pointing as far from each other as possible form a regular tetrahedron, whose bond angle is acos(-1/3), about 109.47°. The lab reports this value.
Eight: eight corner atoms shared by eight cells, six face atoms shared by two, and four atoms wholly inside the cell. The lab shows the sum 8×⅛ + 6×½ + 4.
No. Atoms move about their lattice sites as a teaching illustration, but the equilibrium spacing and density readouts depend only on the lattice parameter you set.