This keyword specifies which calculation method will be used for phonons. SECONDD_METHOD is the latest form of this keyword, while the obsolete version, PHONON_METHOD, is supported for backward compatibility. Available options are:
The finite displacement method produces phonons at the Γ point only.
Using the linear response method imposes restrictions on the calculation settings. Specifically, norm-conserving pseudopotentials must be used, with fixed occupation numbers and without spin polarization.
SECONDD_METHOD : FINITEDISPLACEMENT
CASTEP keyword glossary
CASTEP parameters keywords