Why DFT Density Functional Theory (DFT) DFT is an alternative approach to the theory of electronic structure; electron density plays a central role in DFT. Why a new theory? HF method scales as N4 (N -of basis functions) Cl methods scale as N6-N10 MPn methods scale as >N5 CC methods scale as >N6 >Correlated methods are not feasible for medium and large sized molecules!Why DFT Density Functional Theory (DFT) DFT is an alternative approach to the theory of electronic structure; electron density plays a central role in DFT. Why a new theory? HF method scales as N4 (N - # of basis functions) CI methods scale as N6-N10 MPn methods scale as >N5 CC methods scale as >N6 Correlated methods are not feasible for medium and large sized molecules!