The kernel of **TOSCA** is formed by a set of fortran routines that allow an ab initio non-SCF
calculation by diagonalizing the Kohn-Sham hamiltonian using one of the following
methods:
full or partial diagonalization, diagonalization using the method of Lanczos,
and Arnoldi diagonalization.

Once the eigenvalues and eigenvectors have been computed the following quantities can
be computed by **TOSCA**:

1) Slab polarizability computed with or without real space cutoff, for insulators, semiconductors, metals. Surface epsilon can be also computed;

2) Localization of the wavefunctions for given k-point(s) and states;

3) Squared modulus of a wavefunction for a given k-point and state on the real space FFT grid. Interface with DataExplorer for graphical representation by isosurfaces;

4) RAS (Reflectance Anisotropy Spectra) or SDR (Surface Differential Reflectivity).

**TOSCA** is interfaced in input with a local Car-Parinnello type code and with ABINIT, by reading the wavefunctions outputed by these codes. **TOSCA** can also output a Kohn-Sham structure file that can be
used as input for an abinitio multipurpose Many-Body code SELF.

**TOSCA** contains 190 fortran routines. Routines are mainly written in f77. f90 routines assure the interfacing with
other ab initio codes (ABINIT, ...).