What is the EXC code?

EXC is an exciton code working in reciprocal space, frequency domain, and using plane waves basis. Its purpose is to calculate, ab initio, the dielectric and optical properties, like absorption, reflectivity, refraction index, electron and X-ray energy loss, for a large variety of systems, ranging from bulk systems, surfaces, to clusters or atoms (using the supercell method), by solving the Bethe-Salpeter equation.

The language of the code is Fortran 90, with some insertion of C (parser, utilities) and perl scripts for tests. This release has been tested for the several platforms. Several linear algebra libraries can be linked, thanks to an adaptive interface, either free, like lapack+blas, atlas, or proprietor, like cxml, asl, imsl or essl. The FFTW3 are the preferable fft libraries, but interface with cxml, asl, goedecker-fft are also provided. The goedecker-fft library itself is provided as well.

This code has to be used on top of: (1) a ground state calculation; (2) a gw calculation for the quasi-particle energies (this step can be avoided, if a scissor operator approximation is adopted); (3) rpa plasmon-pole model calculation for the screened Coulomb interaction.