Crystal builder

Choose a cubic prototype, assign elements and a lattice parameter, and read off coordination, density and packing. These are computed from the geometry; they don’t show that a material adopts that structure.

The textbook rocksalt structure; note the computed density against the ≈ 2.16 g/cm³ usually quoted. Lattice parameters are approximate literature values — check the primary source before citing.

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A (fcc): NaX (fcc + ½½½): ClDrag to rotate · atom size shows period only

Nearest-neighbour bondsCell edgesCells

Rocksalt (NaCl) · Fm-3m (225). Two fcc lattices offset by (½,½,½): 6-fold (octahedral) coordination for both.

Compare the prototypes (computed from each geometry)

Atoms / cell	Type	Coordination	NN dist.
1	A	A 6	1.000 a
2	A	A 8	0.866 a
4	A	A 12	0.707 a
8	A	A 4	0.433 a
2	AX	A 8 · X 8	0.866 a
8	AX	A 6 · X 6	0.500 a
8	AX	A 4 · X 4	0.433 a
12	AX2	A 8 · X 4	0.433 a
4	AX3	A 12 · X 12	0.707 a

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Prototype

A element

X element

Candidate

NaCl

8 atoms per cubic cell · AX type AX

Lattice parameter a (Å)

Preset values are approximate literature numbers. For a new combination this is a placeholder you set — not a prediction.

Coordination of Na (A): 6
Coordination of Cl (X): 6
Nearest-neighbour distance: 2.820 Å
Density: 2.164 g/cm³

Charge balance. Charges can balance using common oxidation states. This is a rule-of-thumb check, not proof the compound exists.Na⁺ Cl⁻

Radius-ratio rule. r(cation)/r(anion) = 1.02/1.81 = 0.564, which suggests 6-fold coordination (octahedral); this prototype has 6. Consistent.

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What this result is — and isn’t

User-built candidate. You chose this composition / Rocksalt (NaCl). Choosing elements does not mean the compound exists.
Rule-based assessment. Charges can balance; radius ratio 0.56 matches this prototype.
Database-supported material. Not checked. Compare with a structure database (e.g. ICSD, Crystallography Open Database, Materials Project) before saying a compound adopts this structure.
Calculated result. Only simple geometric quantities (coordination, density, packing) from the prototype and your lattice parameter. No energies or relaxation.