A FAST TDDFT calculation needs information on the system from the underlying DFT calculation, such as the geometry, the molecule wavefunctions, the pseudo potentials, the Hamiltonian and overlap matrices etc. When not compiled to be run coupled to SIESTA via MPICPL, the FAST program gathers this information from the .DIM (geometry), .WFSX (packed wavefunctions), .HSX(Hamiltonian,...) and .PLD (charge density) SIESTA output files. To generate these files the following two keywords must be present in the input file of SIESTA.
COOP.Write .true. WriteDenchar .true.The reader is referred to the SIESTA manual for further details.