# DFPT vs Finite Difference Method [duplicate]

Which one is better in case of a phonon calculation and does DFPT also have small negative frequencies near Gamma due to the numerical noise? What are their advantages and disadvantages?

• The fact that for DFPT you only need to use a primitive cell is not a computational limitation, it is an advantage. Supercells are needed in finite differences because to describe a phonon of wave vector $\mathbf{q}$ you need a supercell commensurate with it. This somewhat limits finite differences because sometimes you cannot build a large enough supercell to do the calculation you want. In DFPT, you can have a phonon of any wave vector in the primitive cell, so if DFPT is available, it is computationally better, not worse. Aug 15 '20 at 18:36