Another option besides PDB and XYZ coordinates formats is XSF, as defined by the XCrySDen visualization program. Specify the filename with this variable. The lattice vectors will also be read from this file and the value of PeriodicDimensions needs to be compatible with the first line (CRYSTAL, SLAB, POLYMER, or MOLECULE). The file should not contain ATOMS, CONVVEC, or PRIMCOORD. NOTE: The coordinates are treated in the units specified by Units and/or UnitsInput.