[SIESTA-L] how to reply the reviewer ?

[caqhero]

Recently, I used the siesta to calculate the optical properties of CNTs. The 
reviewer ask the method I used. and he say that the Ground-state DFT can not 
accurately describe optical properties. I confuse the method for optical 
calculation in siesta. can any body tell me the details ? how can I reply the 
reviewer ? is it  reliable using the siesta to calculate the optical properties 
? any suggestion is appreciated ! thank you !