BCS theory uses tight binding model to explain type-I superconductivity. Theory uses available Gibbs free energy in equilibrium to get transition temperature. Thermodynamics suggest that there is no net Gibbs free energy available in any system

at equilibrium. BCS theory not only undermine this very fundamental thermodynamics principle but also seriously violating the second law of thermodynamics. Secondly, Drude's model and tight binding model suggest that material has finitite conductivity due to the electron scattering either with nucleus or with impurity. Both model are very adhoc model and have very serious fundamental flaw. Becausr, origin of finite conductivity in any material arises due to the pure quantum mechanical effect, in which electron make transition from one Brillouin zone into another next connected Brillouin zones with effectively zero speed (for more information, read my paper "quantum mechanical origin of metal colour and it finite conductivity ). Superconductivity arises due to the presence of flat band near the Fermi energy level. Superconductivity can be very well explain using band structure which come after density functional theory calculations. To me, BCS theory is nothing but a sophisticated bluff that has been played to explain experimented data. This theory will NEVER able to predict any material and it superconducting property. However, using full band structure analysis after classification of bands into different Brillouin zone , one can predict superconducting material and it material property with absolute high precision success rate.