It is common and intuitive to employ the same XC functional for the mean-field ground SCF and the response calculations. However, the use of the same XC function for both problems is not strictly necessary, as time-dependent Kohn-Sham stems from a TDDFT time-dependent exchange-correlation action, and Kohn-sham DFT is based on a static (in time) exchange-correlation functional, despite in practice both functionals are approximated by approximate XC functionals.