# Basic classes

sisl provides basic functionality for interacting with orbitals, atoms, geometries, unit cells and grid functions.

## Simple objects

 Periodic table for creating an Atom, or retrieval of atomic information via atomic numbers Orbital(R[, q0, tag]) Base class for orbital information. SphericalOrbital(l, rf_or_func[, q0, tag]) An arbitrary orbital class where $$\phi(\mathbf r)=f(|\mathbf r|)Y_l^m(\theta,\varphi)$$ AtomicOrbital(*args, **kwargs) A projected atomic orbital consisting of real harmonics Atom(*args, **kwargs) Atomic information, mass, name number of orbitals and ranges Atoms([atoms, na]) A list-like object to contain a list of different atoms with minimum data duplication. Geometry(xyz[, atoms, sc, names]) Holds atomic information, coordinates, species, lattice vectors SuperCell(cell[, nsc, origin]) A cell class to retain lattice vectors and a supercell structure Grid(shape[, bc, sc, dtype, geometry]) Real-space grid information with associated geometry.

The physical matrices used internally in sisl are constructed based on these base classes. However, it may be beneficial to read the specific matrix in Physical quantites.
 Quaternion([angle, v, rad]) Quaternion object to enable easy rotational quantities. SparseCSR(arg1[, dim, dtype, nnzpr, nnz]) A compressed sparse row matrix, slightly different than csr_matrix. SparseAtom(geometry[, dim, dtype, nnzpr]) Sparse object with number of rows equal to the total number of atoms in the Geometry SparseOrbital(geometry[, dim, dtype, nnzpr]) Sparse object with number of rows equal to the total number of orbitals in the Geometry
A set of classes are utility classes that are used throughout the sisl code and using them will be encouraged in combination with sisl.
In particular oplist is useful when calculating averages in Brillouin zones (see Brillouin zone).
 oplist([iterable]) list with element-wise operations PropertyDict Simple dictionary which may access items as properties as well